Start then stall

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heyjewel

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2001 LS6 manual. It starts and 'runs' for a few seconds, then stalls. Consistent failure. This is an engine I just finished rebuilding and reinstalling in my car.
No CEL light or DTCs using scan tool. However the Forscan software shows codes 1237 out of the PCM and 1641 out of the REM. One says fuel pump primary failure the other fuel pump secondary failure.
The fuel pump is new. It MUST be pumping some fuel since the car does start. The crankshaft sensor output MUST be good since I get data on the tach. The relay, fuses and diode associated with the fuel system all test good. If I pull the MAF connector engine runs for a few extra seconds, then dies.
Any ideas?
 
So, I assume that both of those codes start with "P"? That letter is important, and there is more than one possibility for what letter it is...

If those are P codes, then they are both for the REM. There could be a coincidental problem with the REM, or the replacement fuel pump could be drawing too much or too little current for the required flow. Did you replace the whole module, or just the pump in it? If just the pump (aftermarket, I assume) did you get the polarity correct?
 
Can you put a fuel pressure gauge on the rail inlet? I had to troubleshoot a subaru that way once, and had to tape the gauge to the windshield since the problem was intermittent and or instantaneous in nature and you had to operate the key and view the gauge simultaneously.

The gauge would be able to tell you if the fuel system is gradually losing pressure or is instantly losing pressure. Does the exhaust smell like fuel?

In the case of my fuel pressure problem on the subaru, it turned out to be an unlatched connection to the crank position sensor. Interesting note about the MAF sensor. I think that Joe is on the right track, though, since the fuel system on these cars does not have a return bypass line from the rails.

What was the indication that prompted you to change the fuel pump? This problem, or to just have everything new?
 
joegr said:
So, I assume that both of those codes start with "P"? That letter is important, and there is more than one possibility for what letter it is...

If those are P codes, then they are both for the REM. There could be a coincidental problem with the REM, or the replacement fuel pump could be drawing too much or too little current for the required flow. Did you replace the whole module, or just the pump in it? If just the pump (aftermarket, I assume) did you get the polarity correct?
Click to expand...

Yeah, sorry, they're both Ps. I replaced the whole thing with a Spectra.

Forscan associates the 1641 code with the REM and the 1237 with the PCM.
 
milehighmikey said:
Can you put a fuel pressure gauge on the rail inlet? I had to troubleshoot a subaru that way once, and had to tape the gauge to the windshield since the problem was intermittent and or instantaneous in nature and you had to operate the key and view the gauge simultaneously.

The gauge would be able to tell you if the fuel system is gradually losing pressure or is instantly losing pressure. Does the exhaust smell like fuel?

In the case of my fuel pressure problem on the subaru, it turned out to be an unlatched connection to the crank position sensor. Interesting note about the MAF sensor. I think that Joe is on the right track, though, since the fuel system on these cars does not have a return bypass line from the rails.

What was the indication that prompted you to change the fuel pump? This problem, or to just have everything new?
Click to expand...

I have a fuel pressure guage and my next stop is to see if I can attach it to the Schrader valve. BTW there is a good spurt out of that when I press the button in there.
I replaced the fuel pump because before I pulled the engine, the car indicated a 'dry start'. Cranking and cranking and no start. And, yeah, I also wanted a nice clean rebuild and replaced several questionable parts.
 
heyjewel said:
I have a fuel pressure guage and my next stop is to see if I can attach it to the Schrader valve. BTW there is a good spurt out of that when I press the button in there.
I replaced the fuel pump because before I pulled the engine, the car indicated a 'dry start'. Cranking and cranking and no start. And, yeah, I also wanted a nice clean rebuild and replaced several questionable parts.
Click to expand...
I have some updated info about the start and stalling situation on my 2001 Lincoln LS V8 ...I did replace the whole fuel pump assembly today ...after market Spectra brand...I stand behind this brand ...it's a good strong part and I really think those Canadians know how to build a great fuel pump assembly module...anyway As you know from previous conversations about this dilemma...we were both in the same boat and seemingly sinking fast...I remember Joegr saying in the thread I started that if I install the new fuel pump assembly and it continues to provide the same outcome, I should check my REM I researched the REM not knowing what it was and after finding out what it was I thought since the Lincoln LS is one giant computer I may as well unconnected the battery and reboot the PCM so I unconnected the negative battery cable and walked away about 10 minutes later I reconnected the battery cable and proceeded to start the car ....VROOOOOOMMMM!!!! She popped off! The car was running strong and I left it run for a good 5 minutes and then proceeded to drive it around my block ....the fuel pump was working as it should and the car was back to purring like a kitten...By the way checked my plugs today and they looked beautiful...I must admit I've been hearing a bit of a whistle or higher pitch humming the last year or so not sure what it is very faint and never has effected the car while running so just ignore it...can only hear it when hood is open ...but yeah maybe try disconnecting the battery ....it worked for me ...thinking because the computer had to make up for loss of fuel due to my messed up makeshift connector ...when the new connector was installed and proper fuel was regulating the PCM or REM went hay wire for lack of a better term ....anyway that's my story and sticking to it...all my best
 
SO we did some more work on this today. Not solved yet. We cleaned MAF - no help. Then we concentrated on fuel pump and associated wiring. The only progress is that, if we apply 12v and ground across the fuel pump motor the car starts and runs like it should. So something is not providing the proper signal to the pump after the engine starts. I need to check for a good ground on the cable to the fuel pump connector. I've got 12v there and another pin with some voltage but the other two seem to be floating. I've also pulled all three firewall connectors to PCM looking for bent or pushed pins. Cant see any but cant see em all. Later I'm going to apply some contact cleaner spray followed by dielectric grease to those connectors.
More input certainly welcome.
 
The REM drives the fuel pump, not the PCM. Positive battery power to the fuel pump is switched by a relay in the junction box in the trunk. "Ground" to the fuel pump is PWM'd by FETs in the REM. The PCM tells the REM how much power to apply to the fuel pump based on fuel pressure and expected engine demands.
As a safety, the fuel pump is switched off if it looks like the engine has stalled.

What does you scan tool say about the drive level of the fuel pump in real time?
 
joegr said:
The REM drives the fuel pump, not the PCM. Positive battery power to the fuel pump is switched by a relay in the junction box in the trunk. "Ground" to the fuel pump is PWM'd by FETs in the REM. The PCM tells the REM how much power to apply to the fuel pump based on fuel pressure and expected engine demands.
As a safety, the fuel pump is switched off if it looks like the engine has stalled.

What does you scan tool say about the drive level of the fuel pump in real time?
Click to expand...

Yeah I'm getting +12 from that relay. I understand PWM. Not easy to check that since engine dies so quick. In fact it seems that the fuel pump being switched off or not getting the PWM is what's causing engine to stall. However maybe it IS being told to shutdown by some logic in the REM or PCM?
Yes my understanding is the REM drives the pump according to the commands it receives from the PCM (duty cycle of PWM, maybe more?). And it's my understanding that the PCM must be fed certain inputs (fuel rail pressure, crankshaft sensor, fuel intake temperature and maybe more to decide on the output to the REM.

I'll have to see if I can get forscan to provide that drive level signal.

Thanks!
 
Last edited:
OK so I cleaned all three PCM connectors with contact cleaned, sprayed air in there to get anything else out. Spread dielectric grease on the females, rubbed it in and then cleaned top off with a cloth. Put all three back in carefully and securely. Nothing changed.
Hooked up forscan and measured the FP parameter which is the duty cycle out. It is sitting at 75% with a spike down to 8% for a few millisec when key is turned car starts then stalls and back up to 75%.
 
What does it say for the fuel pressure during this time?
Are you still getting the fuel pump drive fault codes?
 
I guess I didn't start the other two parms I had on the chart which were FP in volts and kPa. code

Yes I am still getting the P1641 out of the REM but nothing out of the PCM. This error and the others occur at configuration read time. I dont know if I can read DTCs during or after engine start?
 
Looking at some info in the DVD manual and found info that the 75% duty cycle signal is the PCM commanding the fuel pump off. So that's what's happening right away after signal goes down to 8% or so it comes right back up to 75.
So I also found that PCM will command pump off if it cannot verify that the engine is running. And I think that should come from the crankshaft sensor. I hope I can get the crank sensor output on the forscan.
 
heyjewel said:
Looking at some info in the DVD manual and found info that the 75% duty cycle signal is the PCM commanding the fuel pump off. So that's what's happening right away after signal goes down to 8% or so it comes right back up to 75.
So I also found that PCM will command pump off if it cannot verify that the engine is running. And I think that should come from the crankshaft sensor. I hope I can get the crank sensor output on the forscan.
Click to expand...
What brand is your crank shaft sensor it definitely sounds like symptoms of a bad or faulty crank shaft sensor connection
 
One other point to check into is oil pressure. Some cars, not sure of the LS, used to monitor oil pressure and would kill the engine if no pressure was sensed. You may wish to visit that connection, if it turns out that the PCM complex does monitor oil pressure.
 
I'm sure the crank sensor is factory. Going to shoot that as soon as I can this AM. Thing that bothers me is that I have RPMs on the tach and seems that must come from this sensor...
I'll look into the oil pressure if the crank doesn't work out.

Thanks to all as always.
 
heyjewel said:
I'm sure the crank sensor is factory. Going to shoot that as soon as I can this AM. Thing that bothers me is that I have RPMs on the tach and seems that must come from this sensor...
I'll look into the oil pressure if the crank doesn't work out.

Thanks to all as always.
Click to expand...
Could it be that the re-building of this engine is like installing a new engine which would mean you would need to have the dealer reprogram certain electronic modules...the newer Chevrolets now have three electronic modules that need to be all lined up together...not sure just throwing out ideas...the other option is to check for air leaks somewhere...is the car running rich or lean?
 
AmsterDutch said:
Could it be that the re-building of this engine is like installing a new engine which would mean you would need to have the dealer reprogram certain electronic modules...the newer Chevrolets now have three electronic modules that need to be all lined up together...
Click to expand...

Nope.
 
joegr said:
Nope.
Click to expand...
joegr, yesterday you asked about fuel pressure when this happens. This AM I ran a graph while I tried to start it. I hope I can descibe it and it makes sense to you:
t=0 I have the key on and the parameters set up and hit the start icon on the forscan and quickly turn the key to start the car.
t=0.1 data begins to be streamed to the scope.
FP starts at 75%, spikes down to 27.08% at about 4+msec and back up to 75% (turned off) at 5.1ms
FRP kPa, starts at 450.2, rises to 450.8, falls back down to 450.2 and immediately back up to 450.8 and stays there. It goes steady state at appx 2.5msec. Such a small change!
FRP volts is shown bouncing up and down but the graph says both up and down = 4.24 volts?

Does this tell us anything, joegr?
 
So this AM I ran the forscan on my greay 2001 LS, the one of three that is running. Good ave. on baseball. Anyway I got values that are in line with what I've read the LS should have.
Fvolts = Key on = 2.18, engine crank = 3.12, engine start = appx 2.80
FkPa = Key on = 200, engine crank = 121.2, engine start = 273
FP% = Key on = 75, engine crank = appx 45, engine start = 29.26

So FRP in volts and kPa are about double these values in the car that starts then stalls.

So what can be causing such a high pressure in the fuel rail?
 
heyjewel said:
...
So what can be causing such a high pressure in the fuel rail?
Click to expand...

I'd actually measure the fuel pressure (with a mechanical gauge) before I would be convinced that the pressure actually is high. Perhaps the fuel pressure sensor is incorrectly reporting a high pressure. That would explain the fuel pump being cut and the engine stalling.
 
joegr said:
I'd actually measure the fuel pressure (with a mechanical gauge) before I would be convinced that the pressure actually is high. Perhaps the fuel pressure sensor is incorrectly reporting a high pressure. That would explain the fuel pump being cut and the engine stalling.
Click to expand...
Had to borrow a valve stem remover before I was able to get a measurement.
Amazing - as my wife cranked and engine started the pressure got barely to 10 psi. Then quickly went back to zero as engine stalled. I know both of those results are bad. Remember I was able to get the car started and stay started by jumping across the fuel pump terminals.
 
heyjewel said:
Had to borrow a valve stem remover before I was able to get a measurement.
Amazing - as my wife cranked and engine started the pressure got barely to 10 psi. Then quickly went back to zero as engine stalled. I know both of those results are bad. Remember I was able to get the car started and stay started by jumping across the fuel pump terminals.
Click to expand...

So ... bad pressure sensor? That's the item at the back end of the rail?

BTW - what is that circular shiny metal thing in the fuel line just before the Schrader?
 
heyjewel said:
So this AM I ran the forscan on my greay 2001 LS, the one of three that is running. Good ave. on baseball. Anyway I got values that are in line with what I've read the LS should have.
Fvolts = Key on = 2.18, engine crank = 3.12, engine start = appx 2.80
FkPa = Key on = 200, engine crank = 121.2, engine start = 273
FP% = Key on = 75, engine crank = appx 45, engine start = 29.26

So FRP in volts and kPa are about double these values in the car that starts then stalls.

So what can be causing such a high pressure in the fuel rail?
Click to expand...
By the sound of it I think you're getting closer to a solution...not insulting your ability and/or intelligence by asking you but ...I have to ask did you double and triple check everything when installing the new fuel hoses that go across the saddle tank sumps? Are all the connectors nice and snug within the Jet and Electric fuel pump assembly module? It seems that my situation was very similar when it came to symptoms and After pondering a bit about this situation I suggest trying to mimick what I did you have nothing to lose...not saying it will work but you never know until you try... remove and drain fuel filter ...reinstall fuel filter...disconnect negative battery cable for at least 10 minutes ...reconnect cable ...proceed to start car ....like I said these are the steps I did when having this problem...I suppose you always have the option to send back fuel pump assembly and have them send you a different one ...never know you might have a defective part...As you can see by this post I'm hoping that this is a mechanism failure and not a electronic issue...keep us posted


 
heyjewel said:
So ... bad pressure sensor? That's the item at the back end of the rail?

BTW - what is that circular shiny metal thing in the fuel line just before the Schrader?
Click to expand...
Could be a bad pressure sensor ...It will have a circular metal shield around it ...sometimes this is called a fuel pressure regulator
 
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