86 hunting idle
Thread Starter
Intermediate
Joined: Jan 2009
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From: Fredericksburg Virginia
How about checking if the IAC passages in the TB are gummed up or dirty?
Another trick is to use a propane torch. With fire off and gas flowing, pull of the connectors to the fan but be careful not to overheat it. Run the tip of the torch along the air hoses and items to see if it changes RPM.
Another trick is to use a propane torch. With fire off and gas flowing, pull of the connectors to the fan but be careful not to overheat it. Run the tip of the torch along the air hoses and items to see if it changes RPM.
Thread Starter
Intermediate
Joined: Jan 2009
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From: Fredericksburg Virginia
I'll definately try the propane.
Team Owner
Joined: Jul 2004
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From: Hartford WI
I did clean out the IAC area as well, put in a new IAC last weekend and figured I'd clean out the TB cavity where it screws into while I had it apart. May do it again because I sprayed some SeaFoam in to the plenum a few days ago, some crud may have invaded the TB and the IAC cavity/seat.
I'll definately try the propane.
I'll definately try the propane.
Thread Starter
Intermediate
Joined: Jan 2009
Posts: 46
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From: Fredericksburg Virginia
Just came in from doing the propane and couldn't find any air coming in from outside. Checked all around the MAF, snorkel, TB and all vacuum lines and connections. Even though I didn't find a leak, I learned a much better way to test than carb cleaner, thanks for the tip!!
I might be able to borrow an old Snap On scanner from a mechanic I know, he's loaned it to me before just for some basic code checking. IIRC it hooked up to the OBD1 port, is that the type of scanner that can pull command idle. It was a pretty elaborate kit. Is there a less elaborate one that you would recommend for purchase?
Team Owner
Joined: Jul 2004
Posts: 28,473
Likes: 3,291
From: Hartford WI
Just have the stock chip as far as I know, no scanner (only a volt/ohm meter) but maybe it's time to invest in one?
Just came in from doing the propane and couldn't find any air coming in from outside. Checked all around the MAF, snorkel, TB and all vacuum lines and connections. Even though I didn't find a leak, I learned a much better way to test than carb cleaner, thanks for the tip!!
I might be able to borrow an old Snap On scanner from a mechanic I know, he's loaned it to me before just for some basic code checking. IIRC it hooked up to the OBD1 port, is that the type of scanner that can pull command idle. It was a pretty elaborate kit. Is there a less elaborate one that you would recommend for purchase?
Just came in from doing the propane and couldn't find any air coming in from outside. Checked all around the MAF, snorkel, TB and all vacuum lines and connections. Even though I didn't find a leak, I learned a much better way to test than carb cleaner, thanks for the tip!!
I might be able to borrow an old Snap On scanner from a mechanic I know, he's loaned it to me before just for some basic code checking. IIRC it hooked up to the OBD1 port, is that the type of scanner that can pull command idle. It was a pretty elaborate kit. Is there a less elaborate one that you would recommend for purchase?
Snorkel doesn't matter. Basically you want everything from the MAF and back. Why? Because before the MAF, WGAS. After the MAF it is measured air.
That would work. Problem with your case is I can take your chip out and flash it with something and you won't know.
Have you checked fuel pressure?
Thread Starter
Intermediate
Joined: Jan 2009
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From: Fredericksburg Virginia
Unless you want to bring it to Chevrolet every time you have an issue, I'd say it is time. Besides, if you get something decent you can use it for different vehicles.
Snorkel doesn't matter. Basically you want everything from the MAF and back. Why? Because before the MAF, WGAS. After the MAF it is measured air.
That would work. Problem with your case is I can take your chip out and flash it with something and you won't know.
Have you checked fuel pressure?
Snorkel doesn't matter. Basically you want everything from the MAF and back. Why? Because before the MAF, WGAS. After the MAF it is measured air.
That would work. Problem with your case is I can take your chip out and flash it with something and you won't know.
Have you checked fuel pressure?
Fuel pressure at ignition on -- 20 psi, engine on -- 38 psi, engine shut down holds between 15-20 for over an hour. Gas tank maintains pressure.
Injectors all ohm in the mid 17.x range.
How are the laptop scanners instead of the fancy kits? Trying to save a few bucks!
Team Owner
Joined: Jul 2004
Posts: 28,473
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From: Hartford WI
I couldn't find a way to check the fuel pressure on the FPR, just on the rail and here is what I've got.
Fuel pressure at ignition on -- 20 psi, engine on -- 38 psi, engine shut down holds between 15-20 for over an hour. Gas tank maintains pressure.
Injectors all ohm in the mid 17.x range.
How are the laptop scanners instead of the fancy kits? Trying to save a few bucks!
Fuel pressure at ignition on -- 20 psi, engine on -- 38 psi, engine shut down holds between 15-20 for over an hour. Gas tank maintains pressure.
Injectors all ohm in the mid 17.x range.
How are the laptop scanners instead of the fancy kits? Trying to save a few bucks!
I'm confused. You turn the key on and it tops out to 20 psi only? With the engine on and the hose off, it looks OK but at the key turn it should be higher than 20. Mine is.
All that tells me is the injector electronics are within each other. Does not tell me how the spray pattern is or what volume they spray at. Some will say it is ok. Use the SOTP dyno. I tend to look down on that way. Nobody could have told me that my injectors were not functioning within a little bit of each other except an injector test. Nobody could say that the collapsed basket filter was restricting flow except the test.
Like THIS? Sure. See the blue screen? It tells you what your desired idle speed is for instance. You can record and graph up to 3 values at a time. Good? Sure. Inconvenient? Depends. More clumsy than a scanner but it can graph stuff more conveniently. So it is a toss up.
Safety Car
Joined: Apr 2011
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I couldn't find a way to check the fuel pressure on the FPR, just on the rail and here is what I've got.
Fuel pressure at ignition on -- 20 psi, engine on -- 38 psi, engine shut down holds between 15-20 for over an hour. Gas tank maintains pressure.
Injectors all ohm in the mid 17.x range.
How are the laptop scanners instead of the fancy kits? Trying to save a few bucks!
Fuel pressure at ignition on -- 20 psi, engine on -- 38 psi, engine shut down holds between 15-20 for over an hour. Gas tank maintains pressure.
Injectors all ohm in the mid 17.x range.
How are the laptop scanners instead of the fancy kits? Trying to save a few bucks!
should be 40. clogged sock.
Should hold 40 for an hour after shut down...or longer.
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Thread Starter
Intermediate
Joined: Jan 2009
Posts: 46
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From: Fredericksburg Virginia
Ignition on fuel pump running 50 psi
Ignition on fuel pump stops, immediately drops to 20
Ignition on no longer holds at 20, slowly goes down
Ran a diag. that Agent 86 had posted on another thread and narrowed the pressure drop to the FP regulator after pinching lines, etc. Also checked the vaccuum on the FPR and it won't hold any vacuum (maybe thats normal?).
Looking around for a FPR I see them from $50 to over $200. The $50 looks like replacement bladders and spring, will this work or should I get the entire unit?
Thanks
Team Owner
Joined: Jan 2003
Posts: 20,322
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From: Summerland B.C. Canada
Team Owner
Joined: Jul 2004
Posts: 28,473
Likes: 3,291
From: Hartford WI
I guess I don't care at this point if that is all the fuel pressure it can hold. If it gets 20 after the pump is off, this means he is working the hell out of the pump to get the pressure desired. Next thing to go might be the pump.
Thread Starter
Intermediate
Joined: Jan 2009
Posts: 46
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From: Fredericksburg Virginia
The vac gauge did pull off moist so I went ahead and replaced the bladder/spring combo. The FPR holds vacuum now!!
Pulled the fuel pump to check and clean the sock, everything seemed ok. It obviously has been replaced before.
Pulled the fuel filter, not restricted at all.
Blew air through the fuel lines while disconnected, some crud came out!
Plenum is off right now, going out to clean it and the runners, and will pull the EGR and clean the intake as good as I can. Lots of carbon in the top of this engine. Will also be cleaning the TB again to make sure the IAC seats well.
Any other thoughts while I've got it apart?
Pulled the fuel pump to check and clean the sock, everything seemed ok. It obviously has been replaced before.
Pulled the fuel filter, not restricted at all.
Blew air through the fuel lines while disconnected, some crud came out!
Plenum is off right now, going out to clean it and the runners, and will pull the EGR and clean the intake as good as I can. Lots of carbon in the top of this engine. Will also be cleaning the TB again to make sure the IAC seats well.
Any other thoughts while I've got it apart?
Team Owner
Joined: Jul 2004
Posts: 28,473
Likes: 3,291
From: Hartford WI
The vac gauge did pull off moist so I went ahead and replaced the bladder/spring combo. The FPR holds vacuum now!!
Pulled the fuel pump to check and clean the sock, everything seemed ok. It obviously has been replaced before.
Pulled the fuel filter, not restricted at all. Blew air through the fuel lines while disconnected, some crud came out!
Any other thoughts while I've got it apart?
Pulled the fuel pump to check and clean the sock, everything seemed ok. It obviously has been replaced before.
Pulled the fuel filter, not restricted at all. Blew air through the fuel lines while disconnected, some crud came out!
Any other thoughts while I've got it apart?
Why? And with what did they replace it with? I have gone with a Walbro pump
It never hurts to change the filter. All it takes is one bad load of fuel. I change it once a year, whether it needs it or not. It isn't that expensive.
Have you gotten a decent scanner yet?
Thread Starter
Intermediate
Joined: Jan 2009
Posts: 46
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From: Fredericksburg Virginia
And the new pressure readings are?
Why? And with what did they replace it with? I have gone with a Walbro pump
It never hurts to change the filter. All it takes is one bad load of fuel. I change it once a year, whether it needs it or not. It isn't that expensive.
Have you gotten a decent scanner yet?
Why? And with what did they replace it with? I have gone with a Walbro pump
It never hurts to change the filter. All it takes is one bad load of fuel. I change it once a year, whether it needs it or not. It isn't that expensive.
Have you gotten a decent scanner yet?
Just got everything back together. Still having fuel pressure issues.
45 on ignition for about 1 second, then drops to about 30 and starts to fade, zero within a few minutes.
Just went through Chart A-7A fuel system diagnostic and now it says
"Leaking pump coupling hose or pulsator AND/OR Faulty in tank pump"
Off to get a new pump and sock before the store closes. Also will get some injection hose and loose the pulsator. I spoke to the PO and he never did the fuel pump so it's time anyway, 80,000 miles since he bought it.
Keep you posted, thanks for all your help!
Team Owner
Joined: Jul 2004
Posts: 28,473
Likes: 3,291
From: Hartford WI
Just got everything back together. Still having fuel pressure issues.
45 on ignition for about 1 second, then drops to about 30 and starts to fade, zero within a few minutes.
Just went through Chart A-7A fuel system diagnostic and now it says
"Leaking pump coupling hose or pulsator AND/OR Faulty in tank pump"
Off to get a new pump and sock before the store closes. Also will get some injection hose and loose the pulsator. I spoke to the PO and he never did the fuel pump so it's time anyway, 80,000 miles since he bought it.
Keep you posted, thanks for all your help!
45 on ignition for about 1 second, then drops to about 30 and starts to fade, zero within a few minutes.
Just went through Chart A-7A fuel system diagnostic and now it says
"Leaking pump coupling hose or pulsator AND/OR Faulty in tank pump"
Off to get a new pump and sock before the store closes. Also will get some injection hose and loose the pulsator. I spoke to the PO and he never did the fuel pump so it's time anyway, 80,000 miles since he bought it.
Keep you posted, thanks for all your help!
I wouldn't just rush out to buy a pump. Have you looked at what Walbro offers thru Racetronix?
Team Owner
Joined: Jan 2003
Posts: 20,322
Likes: 248
From: Summerland B.C. Canada
Thread Starter
Intermediate
Joined: Jan 2009
Posts: 46
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From: Fredericksburg Virginia
Getting better
Thanks for everyones' input. Getting better but still not quite right.
Fuel pressure when I started this thread. "Fuel pressure at ignition on -- 20 psi, engine on -- 38 psi, engine shut down holds between 15-20 for over an hour. Gas tank maintains pressure."
Now after FPR, sock, pump and eliminating the pulsator -- ignition on 43psi!!, engine idling 33 psi, shut down slowly leaks down to about 15 after 10 minutes, I'm sure it will continue to fall.
The pressure in the gas tank is much less than it used to be, not a big whoosh when I unscrew the cap.
Reset AIC (a bit higher than spec) and TPS at .54, idles considerably better now but still stumbles at idle every once in a while, was between 400-800 now 500-700 and less intermittent. Runs much better while driving!
On the injectors possibly leaking, pulled the plugs and non are fouled or wet. Ohm'd the cold start at 4.5 just to check. Did not do a leak check when the plenum was off.
Cap, rotor and plugs haven't been done in 80K miles and don't look very good. A few wires have bare spots that have been taped over, the rotor tip and contacts inside the cap are scorched a bit.
Thanks again to all, this fuel pressure loss is still driving me crazy, all connections on lines are dry any other suggestions?
Fuel pressure when I started this thread. "Fuel pressure at ignition on -- 20 psi, engine on -- 38 psi, engine shut down holds between 15-20 for over an hour. Gas tank maintains pressure."
Now after FPR, sock, pump and eliminating the pulsator -- ignition on 43psi!!, engine idling 33 psi, shut down slowly leaks down to about 15 after 10 minutes, I'm sure it will continue to fall.
The pressure in the gas tank is much less than it used to be, not a big whoosh when I unscrew the cap.
Reset AIC (a bit higher than spec) and TPS at .54, idles considerably better now but still stumbles at idle every once in a while, was between 400-800 now 500-700 and less intermittent. Runs much better while driving!
On the injectors possibly leaking, pulled the plugs and non are fouled or wet. Ohm'd the cold start at 4.5 just to check. Did not do a leak check when the plenum was off.
Cap, rotor and plugs haven't been done in 80K miles and don't look very good. A few wires have bare spots that have been taped over, the rotor tip and contacts inside the cap are scorched a bit.
Thanks again to all, this fuel pressure loss is still driving me crazy, all connections on lines are dry any other suggestions?
Team Owner
Joined: Jul 2004
Posts: 28,473
Likes: 3,291
From: Hartford WI
Now after FPR, sock, pump and eliminating the pulsator -- ignition on 43psi!!, engine idling 33 psi, shut down slowly leaks down to about 15 after 10 minutes, I'm sure it will continue to fall.
The pressure in the gas tank is much less than it used to be, not a big whoosh when I unscrew the cap.
Reset AIC (a bit higher than spec) and TPS at .54, idles considerably better now but still stumbles at idle every once in a while, was between 400-800 now 500-700 and less intermittent. Runs much better while driving!
On the injectors possibly leaking, pulled the plugs and non are fouled or wet. Ohm'd the cold start at 4.5 just to check. Did not do a leak check when the plenum was off.
Cap, rotor and plugs haven't been done in 80K miles and don't look very good. A few wires have bare spots that have been taped over, the rotor tip and contacts inside the cap are scorched a bit.
Thanks again to all, this fuel pressure loss is still driving me crazy, all connections on lines are dry any other suggestions?
The pressure in the gas tank is much less than it used to be, not a big whoosh when I unscrew the cap.
Reset AIC (a bit higher than spec) and TPS at .54, idles considerably better now but still stumbles at idle every once in a while, was between 400-800 now 500-700 and less intermittent. Runs much better while driving!
On the injectors possibly leaking, pulled the plugs and non are fouled or wet. Ohm'd the cold start at 4.5 just to check. Did not do a leak check when the plenum was off.
Cap, rotor and plugs haven't been done in 80K miles and don't look very good. A few wires have bare spots that have been taped over, the rotor tip and contacts inside the cap are scorched a bit.
Thanks again to all, this fuel pressure loss is still driving me crazy, all connections on lines are dry any other suggestions?
I don't think that will matter. The IAC compensates for it till it cannot. So if you open up the TB blades, it lets more air in. At which point, to maintain Command Idle, the IAC will close the screw and shut off the air. Only time you can override it is by cranking up the TB screw so far that the IAC cannot compensate. If so, why bother with an IAC? The IAC is basically a controlled air leak used to control timing. When that fails, it will try to do it by other means. I think it did that with my ignition timing or pulse width. Can't remember. So adjusting it higher doesn't do much. I would seriously suggest a scanner before you make those adjustments.
Ohm test doesn't do much. If you injectors are old, why not take them off and send them out for testing? All of them. The ohm test only says what the resistance is across the 2 terminals. It cannot say what the spray pattern is like nor can it say what the leaking is like.
Change all of them. It causes problems.
Besides getting a scanner?
Thread Starter
Intermediate
Joined: Jan 2009
Posts: 46
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From: Fredericksburg Virginia
Also what rubber thing in the tank? If you mean what I called the "sock" that would be the in tank cloth filter at the bottom of the assembly that sits in the slosh valley.
Thanks