89 corvette, acts like fuel delivery prob in corners on hard throttle
02-09-2013, 08:29 PM
#1
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89 corvette, acts like fuel delivery prob in corners on hard throttle
89 corvette, base model. I do have the hard start problem, hit the key, 3-5 revs car will start. If I rev it about 3-4 revs, back off the key, hit the key for a moment it fires right up. Based on this originally, i checked timing, tps, replaced plugs/cap/rotor as their health was unknown. Borrowed auto parts store fuel press gauge - turn key forward, just about 50lbs, doesn't back off quickly at all.
Hard throttle straight away, pulls strong. Coming out of a turn, simple turn or freeway offramp - really surges, like my foot is on-the-pedal, off-the-pedal, on-the-pedal. Can this still be fuel sloshing around? fuel press reg (although I heard cars run really bad when that goes)?
any other items I am missing? thanks. 177,000 miles on the car.
Hard throttle straight away, pulls strong. Coming out of a turn, simple turn or freeway offramp - really surges, like my foot is on-the-pedal, off-the-pedal, on-the-pedal. Can this still be fuel sloshing around? fuel press reg (although I heard cars run really bad when that goes)?
any other items I am missing? thanks. 177,000 miles on the car.
02-09-2013, 10:07 PM
#2
The cold start is not unusual...hard to say what it is with your car. Crank the starter for 1 SECOND, STOP, Hit the starter again and it WILL fire and run.
From everything that I have learned, this is purging the fuel rails of air, and the 2nd turn of the key has then rails full and spraying fuel where the 1st attempt was simply spraying air thru the injectors. The fuel bleeds off during the night and has to be replaced at the 1st start next morning... You CAN just grind on the starter for 3-4 seconds and it WILL fire and run...and by doing that you are pushing the air out of the rails thru the injectors each time they cycle...takes longer and thats hard on the starter.
Gas tank...your fuel windage tray has broken loose. Its junk. Never seen anyone get one glued back and have it stay. If you search here there is a good, do-able DIY system for constructing a "well" for the pump and pick-up tube & return tube to sit inside, while the whole assembly sits down in the tank. If I have time later I'll send it to you in a PM. Bottom line, it works and you will never feel power loss around a corner again. Mine will run in a hard corner until the last qt is gone. Without power loss.
From everything that I have learned, this is purging the fuel rails of air, and the 2nd turn of the key has then rails full and spraying fuel where the 1st attempt was simply spraying air thru the injectors. The fuel bleeds off during the night and has to be replaced at the 1st start next morning... You CAN just grind on the starter for 3-4 seconds and it WILL fire and run...and by doing that you are pushing the air out of the rails thru the injectors each time they cycle...takes longer and thats hard on the starter.
Gas tank...your fuel windage tray has broken loose. Its junk. Never seen anyone get one glued back and have it stay. If you search here there is a good, do-able DIY system for constructing a "well" for the pump and pick-up tube & return tube to sit inside, while the whole assembly sits down in the tank. If I have time later I'll send it to you in a PM. Bottom line, it works and you will never feel power loss around a corner again. Mine will run in a hard corner until the last qt is gone. Without power loss.
02-09-2013, 10:58 PM
#3
this is purging the fuel rails of air, and the 2nd turn of the key has then rails full and spraying fuel where the 1st attempt was simply spraying air thru the injectors.
You CAN just grind on the starter for 3-4 seconds and it WILL fire and run...and by doing that you are pushing the air out of the rails thru the injectors each time they cycle....
You CAN just grind on the starter for 3-4 seconds and it WILL fire and run...and by doing that you are pushing the air out of the rails thru the injectors each time they cycle....
Key on you are only getting 2 sec of pump run (via the ECM ) until the pump shuts off , not enough to purge the system
and build pressure.
By cranking the engine over, you are activating the pump through the OP switch which runs the pump full time
( until engine OP drops below 4 psi )
02-10-2013, 01:14 PM
#5
Pro
Good to know!! is there any way to program the chip for lets say a 4 sec prime? ...that should get all the air out and fully pressurize the rails.
02-10-2013, 06:27 PM
#6
Race Director
There is a deliberate 8-pulse delay programmed into the ECM. I it probably takes a second/two for that to complete. I think it's a combination of this and the need to repressurize the fuel lines.
This is more obvious when you're able to reconfigure the BIN, eliminate the delay, and observe the change. (which I've done)
Loss of fuel in hard corners is a well-known problem that is most easily cured by running with at least 1/4 if not half a tank of fuel.
You can also increase crank time (to get 4-sec) vs decrease it. Moates piggy-back chip, Moates Burn-2 burner, and free software is what's needed. Good idea to buy an ALDL cable too. Total cost would be about $150.
Half that would get you a chip from PCM4less. But you'd lack the ability to diagnosis and do additional mods.
This is more obvious when you're able to reconfigure the BIN, eliminate the delay, and observe the change. (which I've done)
Loss of fuel in hard corners is a well-known problem that is most easily cured by running with at least 1/4 if not half a tank of fuel.
You can also increase crank time (to get 4-sec) vs decrease it. Moates piggy-back chip, Moates Burn-2 burner, and free software is what's needed. Good idea to buy an ALDL cable too. Total cost would be about $150.
Half that would get you a chip from PCM4less. But you'd lack the ability to diagnosis and do additional mods.
Last edited by GREGGPENN; 02-10-2013 at 06:30 PM.
02-10-2013, 06:56 PM
#7
Running the pump purges air in the lines back to the tank
Key on you are only getting 2 sec of pump run (via the ECM ) until the pump shuts off , not enough to purge the system
and build pressure.
By cranking the engine over, you are activating the pump through the OP switch which runs the pump full time
( until engine OP drops below 4 psi )
Key on you are only getting 2 sec of pump run (via the ECM ) until the pump shuts off , not enough to purge the system
and build pressure.
By cranking the engine over, you are activating the pump through the OP switch which runs the pump full time
( until engine OP drops below 4 psi )
But,
this is what I have observed thru a LOT of testing and observation.
Although the 2nd turn of the key gets you the 2 sec prime as it should, thats not what the engine needs...yeah, thats part of it but what has to happen for some reason is the injectors actually cycling as the eng turns over WITH tension on the fuel system.
I've connected the gauge and done this several mornings when it was stone cold.
Test gauge connected,. KEY to ON---NO cranking yet.
Gauge immediately jumps up to 30s...anywhere between 30-40psi.
IF I rotate the key to crank, it WILL rotate the engine and I can watch the pressure on the gauge flicker just slightly as the engine rotates...this is the injectors cycling and using that pre-tension on the fuel system. That tension will not be replaced until the engine actually fires and runs...so the fuel pressure is dropping at 1-2 psi per second as the engine rotates and the banks L&R cycle the injectors...
This will continue for up to 4 seconds where the pressure has now dropped to 30 or less, and the engine WILL fire and run now. The instant that it fires and rotates on its own the fuel pump runs again and the pressure is restored. The gauge stabilizes, all is as it should be.
BUT,
if I turn the key to ON...watch the pump run 2 seconds, and charge the system to the 30s...I can turn the key OFF, the pressure stays. I can then turn the key to ON again and get MORE pressure than the initial FP run...this time it gets to the usual 39-40 for key ON not running. But, cranking at this point still does not build a fire yet. I still see the injs pulse as the fuel tension drops with each cycle, until about 4 seconds pass then it fires and all is well.
Now, if I were to do the initial key ON to get that 2 sec prime, and let it crank for a second, I will see the pressure initially and see it try to drop as the engine turns over, BUT I will stop before it has a chance to fire. I can then turn the key to ON again, see the full pressure this time, as before, and go ahead and crank it and it will lite up instantly. The ONLY difference between this attempt and ANY other is the fact that the engine was allowed to rotate briefly while there was at least some tension on the fuel system.
So, whats happening when I let it crank for just a second the first time? The crankshaft is turning and the injectors are cycling while under pressure. By watching the gauge and confirming the inj operation and knowing the engine is rotating, I believe that the 2nd 2 sec prime combined with the initial cranking is allowing the rails to purge themselves of air. True, the prime should flush any air thru the return....but what about the air thats in the injector body itself? These inj are slightly different than the stock model, and they could in theory trap air when the tension bleeds down.
Because I can do the KEY-> deal 8 times and get the full 40 psi before actual cranking...and that makes absolutely no difference in how long or when it fires, this leads me to believe that the inj have to cycle in order for any trapped air to be purged.
It works for me, anyway.
If you *(Oz) or anyone else has some thoughts on this I am open to hearing them !
I have chased this for a year and the way the system works and being able to see the inj cycling thru the gauge needle, has helped me form this theory. I'm not real sure if its useful in any way, other than reassuring people that their car WILL start eventually, I enjoy knowing that there is a reason why the damn thing just won;t fire off easily the 1st try everyday...
Key ON...crank for a second, key OFF.
Key ON and crank....fires right away.
Combined, this process is still faster than sitting there holding the key to start for 4 seconds...or longer sometimes and its got to be easier on the starter too!
ANy feedback would be appreciated.
Seriously, think about what is going on with the 2 sec prime, the inj cycling and where any air would go and how...if there is any, it has to exit thru the inj into a cylinder and that cannot happen until the engine is cranking. If air is in the injector itself, it has nowhere to go but thru to the intake valve/port.
I would never have come to this conclusion if I had not seen the test gauges needle behave as it did...Once I understood that the needle was showing the quick pulses from the inj cycling...bumping the system, the rest of this BS came easy...
02-11-2013, 01:21 AM
#8
Race Director
The 2 second fuel rail prime is built in to the FMD (Fuel Modeling Device) chip (U12 on Ludis Langens' schematic). There is no way to change it with programming. It might be possible to change it by changing resistor and/or capacitor values, but I have never heard of anyone doing this and don't know which components to change -- it's not at all obvious from the schematics. The FMD controls a lot of stuff so its associated circuitry is very complex.
The ECM turns on the fuel pump when as it sees DRPs (Distributor Reference Pulses), which occur during cranking as well as when the engine is running. I guess you could test this by removing the distributor cap or some other method to keep the plugs from firing. The 12 volt power connection would need to be there for the ignition module to work.
The ECM turns on the fuel pump when as it sees DRPs (Distributor Reference Pulses), which occur during cranking as well as when the engine is running. I guess you could test this by removing the distributor cap or some other method to keep the plugs from firing. The 12 volt power connection would need to be there for the ignition module to work.
02-11-2013, 05:23 PM
#9
Race Director
The ECM turns on the fuel pump when as it sees DRPs (Distributor Reference Pulses), which occur during cranking as well as when the engine is running. I guess you could test this by removing the distributor cap or some other method to keep the plugs from firing. The 12 volt power connection would need to be there for the ignition module to work.
On these bins, pulses 1-8 specify zero fuel pressure. (Because of the functional difference I observed with my tuning, I assume factory parameters are the same/similar.) If you "up" pulses 1-8 to something in the 40-50% range, you'll get much quicker starting...especially when the engine is warm/hot.
On mine, I only have to touch the key to get ignition. Cold starts are still a BIT longer because of the need to (re)build fuel-rail pressure. But they are faster than OEM starts. FWIW...It helps that I turn the key "on" and wait for the pump to stop whining. Then, I crank it.
Except for cold starts, mine starts right away -- with faster cold-starting. This wasn't true before the reference pulse change described in this post.
I owe this advice to TequilaBoy who'd previously posted this in the forum....Or maybe he sent it via PM? I can't remember....
Last edited by GREGGPENN; 02-11-2013 at 05:31 PM.
02-12-2013, 01:07 AM
#10
Burning Brakes
If you search here there is a good, do-able DIY system for constructing a "well" for the pump and pick-up tube & return tube to sit inside, while the whole assembly sits down in the tank. If I have time later I'll send it to you in a PM. Bottom line, it works and you will never feel power loss around a corner again. Mine will run in a hard corner until the last qt is gone. Without power loss.
02-12-2013, 10:23 AM
#11
Took a while to find this. I wrote this to another member that was having some issues with long sweeping turns on the track where he lost fuel pressure in the corners...
BTW,
I still have this in my car and it works perfectly. Just recently I felt a stumble (loss of fuel pressure) and saw NO gas on the gauge..Just for the fun of it, I used a stick to drop in the tank to see just what was left. Stick came out DRY.
Anyway, happy reading.....
&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&& &&&
Like others have stated, the problem is common yet the fix CAN be costly for the avg street car.
Here is a way to fix this forever and save your fuel pump and add years to it as well.
This is the instruction on "HOW to build a fuel pump WELL"
A gas -sump in other words... cheap, easy and extremely effective.
From a PM that was sent to another member with the same problem. I have posted this several times and think its worthy of a 'sticky' for future reference.
**************************************** **************
No, but it was quite easy once the concept was thought out...
I realized that the return line was pouring fuel in the tank constantly and at the same time the pump was starving when going around corners and even under hard accelleration. When you loose the fuel pressure you also loose the return...so one problem created the other and so did solving one problem fix the other.
The factory windage "tray" (now used to hold pocket change on my dresser) broke away from the tank bottom as do most...I was having a horrible windage problem. I couldn't corner under power at all if the tank was below 1/2.
Not satisfied that the little 1" deep tray was much use AND a PITA to replace back in the tank, I wanted to stick something back in there that would hold enough fuel for at least several seconds running...enough for a long sweeping curve at high speed without slinging the fuel off the pump. 4 seconds is forever at 100+ mph in a decreasing radius turn...hitting the gas coming out of a turn like that and getting nothing....just sucks for lack of a better term.
I picked the LUCAS qt bottle (oil treatment) because it was the right diameter, round, deep (need 5-7"), and petroleum resistant. A common qt oil bottle also works well. (rectangular) Must be able to fit thru the tank opening in the tank top.
I cut the top off so the "well" portion was tall and equal. I cut a slot in a bottom rt edge for the pump strainer to fit thru since that is 3-4" long and will need to sit left-right in the tank. Then I marked approx where the bottle would rest against the return tube assy and stay clear of the float arm. I cut slits at 2 levels and used stainless steel safety wire to tie the side of the bottle onto the return tube and frame. Do not try to go around the whole bottle....just cut it so you're securing the left side to the tube .
This has to hold the bottle over against the tube so the float can never hook an edge or hang in its travel in any way. You might have to cut a slice off the top left edge of the well for float arm clearence if it swings too close. Once started, you'll see exactly what I'm trying to describe...
Then I took a small drill bit, 1/8 maybe, and drilled a couple holes in what would be the rear of the bottle at the bottom so fuel could flow in/out and seek its own level. Insert the whole pump/strainer/float mess in the bottle, making sure the strainer end fits thru the slot cut in the bottle bottom so the end of the strainer is sitting outside the bottle. Secure with the stainless wire thru the bottle and around the return line tube. Orient the bottle to clear the float. Get it tied tight so it does not float around or be moved by sloshing fuel.
I made NO holes in the left or right sides since the lateral forces of cornering might help drain it faster and that defeated the purpose of the design. The holes in the bottom rear allow for the level to equalize slowly. I did not want rapid equalizing anyway,....I would prefer that the 'well' always be deeper than the tank as long as the engine is running. This also serves to keep the bigger trash from getting to the whole strainer...since the strainers end (outside the well) can pull fuel in as well as the portion thats inside the well with the pump. Look at this and try to visualize the way it will be when mounted because the bottle with the strainer sticking out the right edge will be resting on the tank bottom, so you do not want to cause the strainer to be crushed or pinched off when its all bolted down. If done properly the 'well' will be right on the tank bottom and need just a little pressure to get the tank cover plate bolted down...
Oh yeah, the round LUCAS bottle is easier to get back in the tank than the rectangular qt oil bottle...thats why I went with the round well this time....
Drop the whole thing in the tank after double checking the float arm for clearence and secure the pump assembly plate with a new gasket.
I have run hard into a corner with the reserve lite ON and not had the engine stumble from fuel starvation...I installed a new sender assy a few months back, and have not run out of fuel yet, but I have pushed it to where it was reading down to 15 miles left and I put over 19 back in the tank...so I am CERTAIN that I am keeping a deeper fuel level in the "well" than the rest of the tank and that is uneffected by G-forces so far. This well design is part of the fuel pump assy instead of having to attach to the tank bottom where access is difficult and damage cannot be repaired easily.
I am not sure why I'm talking about this....I should be looking for the $5000 to file a patent....
Bottom line, it works.
If you want to build one and have any questions that this does not answer, ask me. Glad to help.
BTW,
I still have this in my car and it works perfectly. Just recently I felt a stumble (loss of fuel pressure) and saw NO gas on the gauge..Just for the fun of it, I used a stick to drop in the tank to see just what was left. Stick came out DRY.
Anyway, happy reading.....
&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&& &&&
Like others have stated, the problem is common yet the fix CAN be costly for the avg street car.
Here is a way to fix this forever and save your fuel pump and add years to it as well.
This is the instruction on "HOW to build a fuel pump WELL"
A gas -sump in other words... cheap, easy and extremely effective.
From a PM that was sent to another member with the same problem. I have posted this several times and think its worthy of a 'sticky' for future reference.
**************************************** **************
No, but it was quite easy once the concept was thought out...
I realized that the return line was pouring fuel in the tank constantly and at the same time the pump was starving when going around corners and even under hard accelleration. When you loose the fuel pressure you also loose the return...so one problem created the other and so did solving one problem fix the other.
The factory windage "tray" (now used to hold pocket change on my dresser) broke away from the tank bottom as do most...I was having a horrible windage problem. I couldn't corner under power at all if the tank was below 1/2.
Not satisfied that the little 1" deep tray was much use AND a PITA to replace back in the tank, I wanted to stick something back in there that would hold enough fuel for at least several seconds running...enough for a long sweeping curve at high speed without slinging the fuel off the pump. 4 seconds is forever at 100+ mph in a decreasing radius turn...hitting the gas coming out of a turn like that and getting nothing....just sucks for lack of a better term.
I picked the LUCAS qt bottle (oil treatment) because it was the right diameter, round, deep (need 5-7"), and petroleum resistant. A common qt oil bottle also works well. (rectangular) Must be able to fit thru the tank opening in the tank top.
I cut the top off so the "well" portion was tall and equal. I cut a slot in a bottom rt edge for the pump strainer to fit thru since that is 3-4" long and will need to sit left-right in the tank. Then I marked approx where the bottle would rest against the return tube assy and stay clear of the float arm. I cut slits at 2 levels and used stainless steel safety wire to tie the side of the bottle onto the return tube and frame. Do not try to go around the whole bottle....just cut it so you're securing the left side to the tube .
This has to hold the bottle over against the tube so the float can never hook an edge or hang in its travel in any way. You might have to cut a slice off the top left edge of the well for float arm clearence if it swings too close. Once started, you'll see exactly what I'm trying to describe...
Then I took a small drill bit, 1/8 maybe, and drilled a couple holes in what would be the rear of the bottle at the bottom so fuel could flow in/out and seek its own level. Insert the whole pump/strainer/float mess in the bottle, making sure the strainer end fits thru the slot cut in the bottle bottom so the end of the strainer is sitting outside the bottle. Secure with the stainless wire thru the bottle and around the return line tube. Orient the bottle to clear the float. Get it tied tight so it does not float around or be moved by sloshing fuel.
I made NO holes in the left or right sides since the lateral forces of cornering might help drain it faster and that defeated the purpose of the design. The holes in the bottom rear allow for the level to equalize slowly. I did not want rapid equalizing anyway,....I would prefer that the 'well' always be deeper than the tank as long as the engine is running. This also serves to keep the bigger trash from getting to the whole strainer...since the strainers end (outside the well) can pull fuel in as well as the portion thats inside the well with the pump. Look at this and try to visualize the way it will be when mounted because the bottle with the strainer sticking out the right edge will be resting on the tank bottom, so you do not want to cause the strainer to be crushed or pinched off when its all bolted down. If done properly the 'well' will be right on the tank bottom and need just a little pressure to get the tank cover plate bolted down...
Oh yeah, the round LUCAS bottle is easier to get back in the tank than the rectangular qt oil bottle...thats why I went with the round well this time....
Drop the whole thing in the tank after double checking the float arm for clearence and secure the pump assembly plate with a new gasket.
I have run hard into a corner with the reserve lite ON and not had the engine stumble from fuel starvation...I installed a new sender assy a few months back, and have not run out of fuel yet, but I have pushed it to where it was reading down to 15 miles left and I put over 19 back in the tank...so I am CERTAIN that I am keeping a deeper fuel level in the "well" than the rest of the tank and that is uneffected by G-forces so far. This well design is part of the fuel pump assy instead of having to attach to the tank bottom where access is difficult and damage cannot be repaired easily.
I am not sure why I'm talking about this....I should be looking for the $5000 to file a patent....
Bottom line, it works.
If you want to build one and have any questions that this does not answer, ask me. Glad to help.
02-12-2013, 06:50 PM
#13
Yessir...thats the best part of this design...the return dumps right next to the pump...the pipe assy is a unit the pump is mounted to, so as the pump is sending fuel, the excess is being returned to the sump,
so in theory the pump can pick up the last of the gas and the sump will have the last bit of gas since it catches the returned fuel...This also helps the pump stay submerged in gas to help keep it cool, and it tends to keep the trash outside of the can since the only way for solid trash to get IN the sump/can is straight down and with fuel sloshing around...thats almost impossible.
The taller the "sump" the better but there is a limit...float arm clearence comes first. Tying the sump "can" against the steel tubing is critical...this keeps the float off the can, and allows everything to operate as it should...its just inside a plastic can now.
I tried tie straps to hold the thing in place...they didn;t fail but they were brittle after a year submerged on gasoline. Thats when I started to use stainless safety wire to hold things in place. Not as pretty but who's looking in there?
Hope it helps..
Much easier with images!
02-18-2013, 10:05 PM
#18
Race Director
On at least the APYP and ARAP bins most commonly used as a base-point for tuning, those reference pulses have an associated percentage of fuel-pump pressure attached to each sequential pulse -- starting from the first pulse. I think the table is called something like "Fuel Pressure by Reference Pulse". (Maybe you don't have that in '86 bins?)
On these bins, pulses 1-8 specify zero fuel pressure. (Because of the functional difference I observed with my tuning, I assume factory parameters are the same/similar.) If you "up" pulses 1-8 to something in the 40-50% range, you'll get much quicker starting...especially when the engine is warm/hot.
On these bins, pulses 1-8 specify zero fuel pressure. (Because of the functional difference I observed with my tuning, I assume factory parameters are the same/similar.) If you "up" pulses 1-8 to something in the 40-50% range, you'll get much quicker starting...especially when the engine is warm/hot.
02-24-2013, 11:38 AM
#19
Burning Brakes
My retirement income is assured!
I'm going to make one of these to solve my 'starvation' problem and start manufacturing them in my kitchen!
Only $49.95 plus shipping and handling.
The icing on the cake is my patented instructions that show you how to install it through the gas filler, and save you from removing your fuel pump.
In all seriousness, thanks a million to LEESVET for this great and inexpensive solution to a really irritating problem!!
Only $49.95 plus shipping and handling.
The icing on the cake is my patented instructions that show you how to install it through the gas filler, and save you from removing your fuel pump.
In all seriousness, thanks a million to LEESVET for this great and inexpensive solution to a really irritating problem!!
03-18-2013, 01:49 AM
#20
Racer
Member Since: Oct 2010
Location: Huntington Massachusetts
Posts: 440
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2 Posts
So I took out my fuel pump this week-end and I found out that someone already tried the fix! You can see the pictures here: https://www.facebook.com/media/set/?...1&l=83ee96323b
The fuel pump strainer looked pretty dirty and I had some black particles at the bottom of the bucket. When I corner hard at the track (especially lefthanders) I have fuel starvation problems. I don't know if the holes in the bucket are too small (just 1 in front and 1 at the back) but if I run with less than 3/4 of a tank I have issues. AutoX does not cause any problem, but now that I am really picking up speed at the track I can feel the problem pretty bad.
I am waiting for the new strainer and fuel filter to come in. If you have suggestions on improvements I should do to the bucket, I'm all ears!
Thanks
Le frog
The fuel pump strainer looked pretty dirty and I had some black particles at the bottom of the bucket. When I corner hard at the track (especially lefthanders) I have fuel starvation problems. I don't know if the holes in the bucket are too small (just 1 in front and 1 at the back) but if I run with less than 3/4 of a tank I have issues. AutoX does not cause any problem, but now that I am really picking up speed at the track I can feel the problem pretty bad.
I am waiting for the new strainer and fuel filter to come in. If you have suggestions on improvements I should do to the bucket, I'm all ears!
Thanks
Le frog