@gregski ... thanks for the advice. Your recommendation has already been done, but only the plugs by me so I will check the distributor bits. The plugs brought all the power back but did nothing for the cold start. I am unclear on what provides the initial gas @ startup but whatever it is, it has failed. If it is supposed to be the fuel pump only, than I am losing system pressure overnight. If there is something that is "squirting" fuel into the throttle body than it is not working. My 2 cents.
Cold Start troubles
- Thread starter squeasel
- Start date
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Please don't overlook the wires, and replace them as well, otherwise your tune up is as effective as sucking a titty through a sweater, LOL
The PCM commands the pump on for a few seconds when you first turn the ignition on to "prime" the fuel system.
If the pump is weak, a leak somewhere in the system, or perhaps a bad relay, you will have cold start issues.
Fuel pressure leak possibility ... question: should the fuel system maintain pressure (overnight say) or does it pressurize in the couple of moments the fuel pump runs before starting? If it is supposed to be pressurized, then I should be able to check by attaching the Fuel Pressure gauge without turning on the pump and test for pressure. If it is to be pressured soley in that 2 second window of fuel pump activity I should be able to test for that as well.
Lastly, the fuel pressure gauge is new to me and I have no corroborating info about its accuracy. Can I attach it to a air tank and compare the Fuel Pressure Gauge reading to a tire pressure gauge reading?
Much Thanks!
Lastly, the fuel pressure gauge is new to me and I have no corroborating info about its accuracy. Can I attach it to a air tank and compare the Fuel Pressure Gauge reading to a tire pressure gauge reading?
Much Thanks!
Dont think air will show the same as fuel....
Hook the guage up, might have some pressure left over from yesterday, next turn ign key on, dont start, take reading as pump is running. This is KOEO pressure.
Next wait and see how long it holds the pressure, we are checking bleed off here, how long does it hold pressure? How far does it drop in 5 min?
Start the engine, with engine at an idle, what is the pressure?
Rev the engine a bit with the RPMS up, what does the pressure do?
Let us know.
Hook the guage up, might have some pressure left over from yesterday, next turn ign key on, dont start, take reading as pump is running. This is KOEO pressure.
Next wait and see how long it holds the pressure, we are checking bleed off here, how long does it hold pressure? How far does it drop in 5 min?
Start the engine, with engine at an idle, what is the pressure?
Rev the engine a bit with the RPMS up, what does the pressure do?
Let us know.
I finally have time to do some additional tests. First, since April, the Cold Start Issue sort of went away. I could start the car by engaging the starter for about 5 seconds, stopping, engaging the starter until I felt a fire, about 2 seconds, then stop, then engage the start and it would start. So that put the problem on the back burner, so to speak.
I started reworking the problem last weekend and noticed that the battery was a bit low 11.9V. So I charged and equalized the battery and put it back in the Tahoe. Since I have done that, the car will not start without gas in the throttle body. Unknown why and maybe unrelated.
Today I have been redoing the Fuel Pressure Checks. Here are the results:
Put the gauge on the testing valve: 0 PSI
Ignition to on: 50 psi
Ignition off in 2 minutes drop to : 46 PSI but held steady
Ignition to on: 51 PSI
Ignition to start drop to 40 PSI while starter activated
Add fuel to TBI started with pressure at 52 PSI
On rev up: 61 PSI
Ignition off: 52.5 PSI
Off after 2 min: 58.5 PSI
Drained pressure, ignition to on: 52 PSI
Taking readings often to see what is happening to pressure with ignition off
At T + 23: 62 PSI
Currently quite confused. I will post results after the 4 hours.
Cheers!
I started reworking the problem last weekend and noticed that the battery was a bit low 11.9V. So I charged and equalized the battery and put it back in the Tahoe. Since I have done that, the car will not start without gas in the throttle body. Unknown why and maybe unrelated.
Today I have been redoing the Fuel Pressure Checks. Here are the results:
Put the gauge on the testing valve: 0 PSI
Ignition to on: 50 psi
Ignition off in 2 minutes drop to : 46 PSI but held steady
Ignition to on: 51 PSI
Ignition to start drop to 40 PSI while starter activated
Add fuel to TBI started with pressure at 52 PSI
On rev up: 61 PSI
Ignition off: 52.5 PSI
Off after 2 min: 58.5 PSI
Drained pressure, ignition to on: 52 PSI
Taking readings often to see what is happening to pressure with ignition off
At T + 23: 62 PSI
Currently quite confused. I will post results after the 4 hours.
Cheers!
Bleed off sounds good, but your Key On Engine Off sounds low, should be closer to 60PSI with prime. Could be a weak pump. Might hook a set of jumper cables to it with another rig running (so your system voltage is 14 volts and you get a bit better pressure) then see how it starts.
lesterl: I will try more electricity.
Fuel system leakage test ... started after ignition in the on setting to pressurize. After intitial pressurization, nothing else done except for taking readings. The pressure tester gauge was attached the entire time:
Start at time 0 with 53 psi
T+23 minutes: 62 psi 9 (yes, it went up almost 10 lbs in 20+ minutes ... huh?)
T+60 (1 hour): 61 psi
T+118 (c. 2 hours): 61 psi
T+176 (c. 3 hours): 60 psi
T+240 (4 hours): 52 psi
T+296 (c. 5 hours): 30 psi
T+360 (6 hours): 24 psi
T+420 (7 hours): 9 psi
T+472 (< 8 hours): 0 psi
I have no clue what this means. I did think that this system was supposed to remain pressurized. Mine, obviously, does not. Suggestions welcome.
Fuel system leakage test ... started after ignition in the on setting to pressurize. After intitial pressurization, nothing else done except for taking readings. The pressure tester gauge was attached the entire time:
Start at time 0 with 53 psi
T+23 minutes: 62 psi 9 (yes, it went up almost 10 lbs in 20+ minutes ... huh?)
T+60 (1 hour): 61 psi
T+118 (c. 2 hours): 61 psi
T+176 (c. 3 hours): 60 psi
T+240 (4 hours): 52 psi
T+296 (c. 5 hours): 30 psi
T+360 (6 hours): 24 psi
T+420 (7 hours): 9 psi
T+472 (< 8 hours): 0 psi
I have no clue what this means. I did think that this system was supposed to remain pressurized. Mine, obviously, does not. Suggestions welcome.
The pressure drop is normal AFAIK, nothing is perfect. The Pressure increase is abnormal. Unless the fuel in the lines was heating up and expanding or something?
Perhaps you have a sticking fuel pump relay or something?
Perhaps you have a sticking fuel pump relay or something?
Hi LesterL, thanks for the response. The lines should have been heating up, the car was not running and the external temperature was not changing nor was it hot. I have swapped fuel pump relays so I don't think that is an issue. I did not hear the fuel pump running when the pressure increased and it did so in a consistent (slow and steady) manner. To me, this suggests that the fuel system may be generating the necessary pressure, but that it is unevenly distributed (i.e. something is blocked and the system pressure is normal or high in one area and low in another ... thus over the 20 minutes though pressure leakage, the system pressure evened out).
I like your idea (I think it was yours) to jump start the car. I am concerned the battery is underperforming.
And perhaps I don't understand the role of the pressure regulator in this issue. Does it not instruct the pump (via the computer) to turn on and off?
I like your idea (I think it was yours) to jump start the car. I am concerned the battery is underperforming.
And perhaps I don't understand the role of the pressure regulator in this issue. Does it not instruct the pump (via the computer) to turn on and off?
I had a similar issue charging my last AC system, it sucked down kinda slow, I shut off the valve and pump to see if it would hold vac and it jumped up a few psi (ended up having to wiggle the hose I had attached a bit and I think the schrader valve hadnt opened much to begin with, so after messing with the hose the port fully opened and it sucked down fast, held good, charged good.
As far as the FPR, its only purpose is to "bleed" off excess pressure back to the fuel tank, it is a diaphram operated device with a spring that holds the port shut, when the fuel pressure is high enough pushing against the spring held shut port the fuel flows past and to the tank. The FPR also has vacume feed that can modify fuel pressure also.....
As far as the FPR, its only purpose is to "bleed" off excess pressure back to the fuel tank, it is a diaphram operated device with a spring that holds the port shut, when the fuel pressure is high enough pushing against the spring held shut port the fuel flows past and to the tank. The FPR also has vacume feed that can modify fuel pressure also.....
Follow Up on the Cold Start Trouble: I have replaced the old FI with a new Delphi MFI system. The truck fires up immediately when cold so I am calling the problem solved. I will do more tests and report. Yes, it does take me this long to finish projects (10 months in this case). -Bret
Greetings All! It has been several days with the new MFI and the Tahoe has started quickly every time asked. The truck is running very well, with better power, consistency and smoothness. It is an effortless and sneaky romp to 60 MPH. I am very pleased with the new MFI unit. I am the original owner of the car and do not recall when it performed better (though it might have in the early days). Also, I am eager to try it with a trailer load (MB 6.3 might move from storage to the fix-it garage LOL).
MFI surgery: As many have already documented, the MFI upgrade is a simple but time consuming process (time consuming for me at least). The first step is safety ... disconnect the battery and bleed the fuel pressure (not necessary in my case). Second step is to disconnect the wiring harness that runs over the intake manifold plenum. There is a line that runs front/back ... everything needs to be removed ... and a line that runs right/left at the back of the engine ... the local connections need to be removed but the bulk of the harness does not. There are a couple of vacuum lines to remove as well. I took the time to label all connections. Remove the fuel lines from the FI to the join at the rear of the engine (8mm, I think, at the FI and 16mm or 5/8? and 20 mm at the back .... I used 5/8 open end somewhat short handle but had to buy an adjustable wrench with 24mm jaw spread but 6-inch handle for the 20mm spec). Next, remove the objects attached to the the top of the plenum stud nuts (doesn't sound right), then remove the plenum studs (10mm deep socket does the trick for all of this). I had a stuck stud nut problem but others may not. Remove plenum ... remove spider legs, they just pull out ... remove FI from bracket, then remove bracket ... allen wrench needed here. I put in a new plenum gasket and a new FI gasket. Assembly opposite of removal, as they say.
I hope this helps.
MFI surgery: As many have already documented, the MFI upgrade is a simple but time consuming process (time consuming for me at least). The first step is safety ... disconnect the battery and bleed the fuel pressure (not necessary in my case). Second step is to disconnect the wiring harness that runs over the intake manifold plenum. There is a line that runs front/back ... everything needs to be removed ... and a line that runs right/left at the back of the engine ... the local connections need to be removed but the bulk of the harness does not. There are a couple of vacuum lines to remove as well. I took the time to label all connections. Remove the fuel lines from the FI to the join at the rear of the engine (8mm, I think, at the FI and 16mm or 5/8? and 20 mm at the back .... I used 5/8 open end somewhat short handle but had to buy an adjustable wrench with 24mm jaw spread but 6-inch handle for the 20mm spec). Next, remove the objects attached to the the top of the plenum stud nuts (doesn't sound right), then remove the plenum studs (10mm deep socket does the trick for all of this). I had a stuck stud nut problem but others may not. Remove plenum ... remove spider legs, they just pull out ... remove FI from bracket, then remove bracket ... allen wrench needed here. I put in a new plenum gasket and a new FI gasket. Assembly opposite of removal, as they say.
I hope this helps.
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