Hard Cold Start C4
Thread Starter
2nd Gear
Joined: Nov 2006
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Hard Cold Start C4
HELP. I have a 1990 vette that I am having trouble figuring out why it will not start after sitting over night. Had it to 2 different Cheverolet dealers and they have not been able to fix it. I personally have changed the plugs, distributer cap & rotor and engine coolant temperature switch. The first dealership stated I had low fuel pressure 42 lbs, but it dropped of quickly when the pump shut off. I changed the fuel pump, pulsater, sock and and fuel filter. Still no luck, same symptoms. The second dealership stated the pressure was still low, asked what kind of pump was installed. I had bought a pump from auto zone, Bosh. The said that was the problem. Took out the bosh and I installed an AC Delco, bought from the dealership and did away with the pulsator. Still same problem. The ejectors have been tested and they tested good. Car runs perfect after starting and starts great when warmed up. The car starts imediately when cold if I give it a squirt of starting fluid so I am assuming it is fuel related, maybe bad pressure regulator?? Has any one run into this problem and been able to solve it. Thanks for any input.
Last edited by jsmykl; Nov 18, 2006 at 02:57 PM.
Le Mans Master
Joined: Feb 2006
Posts: 8,753
Likes: 9
From: Louisiana
Did you ohm test or leak test the injectors?
Does fuel pressure build after the key is turned "on" not cranked?
Have you looked into the FPR vacuum line for signs of fuel?
Have you looked at the spark plugs for gas fouling?
There are only so many causes for a drop in fuel pressure after the pump stops. Leak in the metal or rubber fuel lines or connections/fuel filter connection, check valve, pulsator, FPR, injectors. The 42 psi sould pretty normal to me. Hope you kept the Bosch fuel pump.
The fuel pump relay is activated by the ECM after the key is turned "on", but for only 2 seconds. The oil pressure switch is the back up for the fuel pump relay and closes the circuit after the oil pressure reaches ~4 psi.
Does fuel pressure build after the key is turned "on" not cranked?
Have you looked into the FPR vacuum line for signs of fuel?
Have you looked at the spark plugs for gas fouling?
There are only so many causes for a drop in fuel pressure after the pump stops. Leak in the metal or rubber fuel lines or connections/fuel filter connection, check valve, pulsator, FPR, injectors. The 42 psi sould pretty normal to me. Hope you kept the Bosch fuel pump.
The fuel pump relay is activated by the ECM after the key is turned "on", but for only 2 seconds. The oil pressure switch is the back up for the fuel pump relay and closes the circuit after the oil pressure reaches ~4 psi.
Pro
Joined: Aug 2004
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Originally Posted by jsmykl
HELP. I have a 1990 vette that I am having trouble figuring out why it will not start after sitting over night. Had it to 2 different Cheverolet dealers and they have not been able to fix it. I personally have changed the plugs, distributer cap & rotor and engine coolant temperature switch. The first dealership stated I had low fuel pressure 42 lbs, but it dropped of quickly when the pump shut off. I changed the fuel pump, pulsater, sock and and fuel filter. Still no luck, same symptoms. The second dealership stated the pressure was still low, asked what kind of pump was installed. I had bought a pump from auto zone, Bosh. The said that was the problem. Took out the bosh and I installed an AC Delco, bought from the dealership and did away with the pulsator. Still same problem. The ejectors have been tested and they tested good. Car runs perfect after starting and starts great when warmed up. The car starts imediately when cold if I give it a squirt of starting fluid so I am assuming it is fuel related, maybe bad pressure regulator?? Has any one run into this problem and been able to solve it. Thanks for any input.
Put a fuel pressure guage on it and see what happens during this cycle.
Thread Starter
2nd Gear
Joined: Nov 2006
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The fuel pump relay was replaced before posting this thread. The relay contacts were intermitten, so I replaced the relay. Fuel pump does run for the 2 seconds when turning the switch on. The injectors were ohmn tested, but not leak tested. The spark plugs are not wet after cranking, so I suspect the problem is not flooding due to injector leak. The fuel pressure imediately rises to 43-44 psi upon turning the key, but drops quickly after that. The pulsator was eliminated when the fuel pump was replaced, fuel hose and clamps used to replace. The hose was taken off the fuel pressure regulator, no gas detected. I have checked the supply lines\hoses, no leaks found.
Thanks for all your suggestions, any more places to look would be appreciated.
By the way, what is the troubleshooting guide in the FSM?
Thanks for all your suggestions, any more places to look would be appreciated.
By the way, what is the troubleshooting guide in the FSM?
Last edited by jsmykl; Nov 18, 2006 at 07:49 PM.
Le Mans Master
Joined: Feb 2006
Posts: 8,753
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From: Louisiana
Take the gas lid and rubber boot off. You will see three lines coming from the fuel pump assembly. As soon as you turn the key "on" and get fuel pressure pinch off the top right rubber hose (fuel feed line) above the tank. If the pressure holds the problem is a leaky intank pump hose or pulsator or faulty fuel pump (check valve). If it doesn't hold, use the same procedure and pinch off the bottom right hose (fuel return line). If it holds you have a faulty FPR and if it doesn't hold locate the leaky injector.
Le Mans Master
Joined: Dec 2000
Posts: 7,839
Likes: 22
From: San Diego, Ca
If it eventually starts, it's more than likely the injectors. Do make sure the battery is fully charged and you might just try priming the rail a couple of times by turning the key on and then off and back on (leaving it on each time for a couple of seconds) and then trying to start it. If it fires, I'd replace them - a cheapo set of Accels did wonders for me (and it left the showroom floor with a hard cold start) so after living with it for 12 Years, it was a nice change. By the way, my stock tested fine.
Pro
Joined: Aug 2004
Posts: 623
Likes: 1
Originally Posted by jsmykl
The fuel pump relay was replaced before posting this thread. The relay contacts were intermitten, so I replaced the relay. Fuel pump does run for the 2 seconds when turning the switch on. The injectors were ohmn tested, but not leak tested. The spark plugs are not wet after cranking, so I suspect the problem is not flooding due to injector leak. The fuel pressure imediately rises to 43-44 psi upon turning the key, but drops quickly after that. The pulsator was eliminated when the fuel pump was replaced, fuel hose and clamps used to replace. The hose was taken off the fuel pressure regulator, no gas detected. I have checked the supply lines\hoses, no leaks found.
Thanks for all your suggestions, any more places to look would be appreciated.
By the way, what is the troubleshooting guide in the FSM?
Thanks for all your suggestions, any more places to look would be appreciated.
By the way, what is the troubleshooting guide in the FSM?
1. Grossly leaking injector or injectors.
2. Faulty FPR
3. bad check valve in fuel pump.
4. bad pulsator.
5. ruptured or leaking line.
I may have forgotten one or two but I think you get my drift. I could find the cause in less than one hour.
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Le Mans Master
Joined: Dec 2000
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From: San Diego, Ca
Wow - took me 12 Years - and yes, I ran all the tests - even bought a tool to energize each one and record the pressure drop. After buying a new set, sent them to Rich at Cruizin' Performance and he told me they tested fine, but wasn't surprised to hear about the hard cold start.
Go figure. This guy has a new pump (his second). He's checked the regulator and clamping the return line and letting it rise above 60 psi can kill it. Nothing wrong with checking the plugs or pulling the rail and with a paper towel underneath, see if any drip - but if you've gone that far on a 17 year old car??? Seems you just fork over 250 Bucks and replace them.
Go figure. This guy has a new pump (his second). He's checked the regulator and clamping the return line and letting it rise above 60 psi can kill it. Nothing wrong with checking the plugs or pulling the rail and with a paper towel underneath, see if any drip - but if you've gone that far on a 17 year old car??? Seems you just fork over 250 Bucks and replace them.
Pro
Joined: Aug 2004
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Originally Posted by SunCr
Wow - took me 12 Years - and yes, I ran all the tests - even bought a tool to energize each one and record the pressure drop. After buying a new set, sent them to Rich at Cruizin' Performance and he told me they tested fine, but wasn't surprised to hear about the hard cold start.
Go figure. This guy has a new pump (his second). He's checked the regulator and clamping the return line and letting it rise above 60 psi can kill it. Nothing wrong with checking the plugs or pulling the rail and with a paper towel underneath, see if any drip - but if you've gone that far on a 17 year old car??? Seems you just fork over 250 Bucks and replace them.
Go figure. This guy has a new pump (his second). He's checked the regulator and clamping the return line and letting it rise above 60 psi can kill it. Nothing wrong with checking the plugs or pulling the rail and with a paper towel underneath, see if any drip - but if you've gone that far on a 17 year old car??? Seems you just fork over 250 Bucks and replace them.
Le Mans Master
Joined: Feb 2006
Posts: 8,753
Likes: 9
From: Louisiana
Originally Posted by RRT vette
Take the gas lid and rubber boot off. You will see three lines coming from the fuel pump assembly. As soon as you turn the key "on" and get fuel pressure pinch off the top right rubber hose (fuel feed line) above the tank. If the pressure holds the problem is a leaky intank pump hose or pulsator or faulty fuel pump (check valve). If it doesn't hold, use the same procedure and pinch off the bottom right hose (fuel return line). If it holds you have a faulty FPR and if it doesn't hold locate the leaky injector.
Pro
Joined: Aug 2004
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Likes: 1
Originally Posted by RRT vette
To clear my statment up...just let the fuel pump run for the 2 seconds after the key is turned on. Don't try and pinch off the lines with the pump running.
Le Mans Master
Joined: Dec 2000
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From: San Diego, Ca
Well duh - forgot to suggest the other thing - Check the Engine Coolant Temp Signal (since it replaces the choke) - should be ambient (along with the Air Temp Signal) on a cold engine. You'll need a scanner to see what the ECM is sensing, but if the fan happens to be running (make sure the a/c is off), that's a another clue. I know you replaced it, but that doesn't rule out the ECM or the wiring and though you could wring out the wiring with a DVM, that still won't tell you what the ECM is doing.
Last edited by SunCr; Nov 18, 2006 at 11:03 PM.
Team Owner
Joined: Mar 2001
Posts: 54,124
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From: Cincinnati, Oh USA
It won't start because there is no fuel pressure and the injectors are not spraying fuel. The proof is when you can get it to start with starting fluid, but not without it and you admit the fuel pressure drops rapidly. The fuel pressure has to stay up long enough to start the engine during cranking and yours isn't staying up long enough. You need to find out why the fuel pressure drops so rapidly. Check out each of the 5 reasons lefoy84 listed in his post as to why fuel pressure drops rapidly.
Safety Car
Joined: Jul 2004
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Originally Posted by SunCr
Well duh - forgot to suggest the other thing - Check the Engine Coolant Temp Signal (since it replaces the choke) - should be ambient (along with the Air Temp Signal) on a cold engine. You'll need a scanner to see what the ECM is sensing, but if the fan happens to be running (make sure the a/c is off), that's a another clue. I know you replaced it, but that doesn't rule out the ECM or the wiring and though you could wring out the wiring with a DVM, that still won't tell you what the ECM is doing.
Advanced
Joined: Nov 2005
Posts: 54
Likes: 1
From: San Jose California
Originally Posted by Da Mail Man
..hey suncr, i know you have "participated" in a few threads of mine regarding my chronic hard start issues. that in mind, if the Engine Coolant Temp Signal is messed up from the sensor and that device acts as a "choke" (so-to-speak), do you think that could be the reason i have to hold my pedal to the floor to speed up the start time and lower the cranking time? i am aware of the "flood mode" with the pedal to the floor. i also have an auto x-ray scanner and such, what would i be looking for as i am a novice with that device and have seldom used it. thanks!
If it is a lot higher than the ambient air temp then you most likely have a bad Engine Coolant Temp Sensor or a bad ECM or a compound problem of both (rare though). Change the Temp Sensor first because it's only about $10 from the dealer. After you replace the ECT, scan it again (before you try to start it) and check the Engine Coolant Temp. If it didn't fix the problem, you'll probably need to go with the ECM.
What happens is that the ECT Sensor sends a signal to the ECM as to what the Coolant Temp is. Once the Coolant Temp sensor sends this signal (along with some other sensors sending their info too) the ECM decides how much fuel to deliver, if the ECM thinks the temp is too high, it won't send as much fuel as it would if it decided the temp was too low.
BTW, the ECT Sensor is relatively easy to fix for any DIY mechanic.
Last edited by VetBoy89II; Nov 23, 2006 at 10:29 PM.
Safety Car
Joined: Jul 2004
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Originally Posted by VetBoy89II
After the car has been sitting overnight, hook up your scanner. Read what the Engine Coolant Temperature is. It should be the same as the ambient air temperature; in other words your coolant should be the same temp as the air outside.
If it is a lot higher than the ambient air temp then you most likely have a bad Engine Coolant Temp Sensor or a bad ECM or a compound problem of both (rare though). Change the Temp Sensor first because it's only about $10 from the dealer. After you replace the ECT, scan it again (before you try to start it) and check the Engine Coolant Temp. If it didn't fix the problem, you'll probably need to go with the ECM.
What happens is that the ECT Sensor sends a signal to the ECM as to what the Coolant Temp is. Once the Coolant Temp sensor sends this signal (along with some other sensors sending their info too) the ECM decides how much fuel to deliver, if the ECM thinks the temp is too high, it won't send as much fuel as it would if it decided the temp was too low.
BTW, the ECT Sensor is relatively easy to fix for any DIY mechanic.
If it is a lot higher than the ambient air temp then you most likely have a bad Engine Coolant Temp Sensor or a bad ECM or a compound problem of both (rare though). Change the Temp Sensor first because it's only about $10 from the dealer. After you replace the ECT, scan it again (before you try to start it) and check the Engine Coolant Temp. If it didn't fix the problem, you'll probably need to go with the ECM.
What happens is that the ECT Sensor sends a signal to the ECM as to what the Coolant Temp is. Once the Coolant Temp sensor sends this signal (along with some other sensors sending their info too) the ECM decides how much fuel to deliver, if the ECM thinks the temp is too high, it won't send as much fuel as it would if it decided the temp was too low.
BTW, the ECT Sensor is relatively easy to fix for any DIY mechanic.
Instructor
Joined: Nov 2003
Posts: 102
Likes: 0
From: Fountain Valley CA
Had the same problems with my 89 about 2 years ago; went through the same things that your are doing now.
The problem turned out to be the ECM, it was converting the temp sensor signal higher that what it should have been thus disabling the "rich" injector pulse width needed to start a cold engine. The fact that you can get it started with a shot of starting fluid ( I did that too) makes it a reasonable conclusion.
Also, my idling was screwed up when I did get it started, and, my coolant fan would come on way too early, like 125 degrees.
After I replaced the ECM, all the hard start, idling, and fan come-on problems went away. The car ran like new.
I had the original 165 ECM and when I bought the new one it was already upgraded twice to part number 88999194. I paid $103 for the new one.
BTW, like SunCr said, you will need a scan tool of some sort to read the temp sensor output; I used WinALDL software with my laptop.
Hope this helps; I know what you are going thru: Been there, Done that.
The problem turned out to be the ECM, it was converting the temp sensor signal higher that what it should have been thus disabling the "rich" injector pulse width needed to start a cold engine. The fact that you can get it started with a shot of starting fluid ( I did that too) makes it a reasonable conclusion.
Also, my idling was screwed up when I did get it started, and, my coolant fan would come on way too early, like 125 degrees.
After I replaced the ECM, all the hard start, idling, and fan come-on problems went away. The car ran like new.
I had the original 165 ECM and when I bought the new one it was already upgraded twice to part number 88999194. I paid $103 for the new one.
BTW, like SunCr said, you will need a scan tool of some sort to read the temp sensor output; I used WinALDL software with my laptop.
Hope this helps; I know what you are going thru: Been there, Done that.
Le Mans Master
Joined: Dec 2000
Posts: 7,839
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From: San Diego, Ca
What Year are we dealing with? If it has a Cold Start Injector, you'll need to make sure it's grounded and spraying on start up. Otherwise, checking the CTS with a scanner makes it a lot easier. I lost my ECM too and with the fan running and no fast idle, I knew where to look. You can also simply substitute another CTS (you don't need to install it) and see what happens - compare signals, etc. If you have the original MULTECS, I'd recommend something else, regardless of how they flow.