Rebuilt engine - runs 5 seconds then dies
08-19-06, 06:09 PM
#1
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Rebuilt engine - runs 5 seconds then dies
Originaly the car ran 100% fine. -- Other than blowing plenty of smoke. 1990 S5 n/a
-removed emissions, power stearing pump, rats nest, air pump.
Again, incase I need to re-iterate, car ran fine priror to engine rebuild.
Rebuilt entire engine.
Timing set by aligning yellow pulley mark to front cover mark, and stabbing cas gear aligned with cas mark.
Engine starts fine. Runs about 5-6 seconds on its own at >4krpm, then sputters to stall.
acts like a vacuum leak. Remounted and re-gasketed manifolds 4 times.-- No change.
So rule out vacumm leak.
Next thought is that I have fuel lines backwards. There is 0-zero-none-nill-zilch fuel coming into the return fuel line. There is a huge amount of gas pressure on the line with the fuel filter. This sounds like possibly have the lines reversed?
I have the incoming fuel after the fuel filter going to the lower injector rail on the which then feeds to the injectors on the uim and then returning to the fuel like. There hasn't been any fuel in the return line, even when we started the engine and let it run for its 5 secodns.
What do you all think?
Thanks for your help!
-removed emissions, power stearing pump, rats nest, air pump.
Again, incase I need to re-iterate, car ran fine priror to engine rebuild.
Rebuilt entire engine.
Timing set by aligning yellow pulley mark to front cover mark, and stabbing cas gear aligned with cas mark.
Engine starts fine. Runs about 5-6 seconds on its own at >4krpm, then sputters to stall.
acts like a vacuum leak. Remounted and re-gasketed manifolds 4 times.-- No change.
So rule out vacumm leak.
Next thought is that I have fuel lines backwards. There is 0-zero-none-nill-zilch fuel coming into the return fuel line. There is a huge amount of gas pressure on the line with the fuel filter. This sounds like possibly have the lines reversed?
I have the incoming fuel after the fuel filter going to the lower injector rail on the which then feeds to the injectors on the uim and then returning to the fuel like. There hasn't been any fuel in the return line, even when we started the engine and let it run for its 5 secodns.
What do you all think?
Thanks for your help!
08-19-06, 06:28 PM
#2
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sounds like the FPR... it regulates fuel pressure, not completely stops it. so it COULD be overpressurizing and flooding the car?? i dunno sounded good while typing it.
08-19-06, 07:00 PM
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Possibly, but theres no reason for it to stop working just because I rebuilt the engine?
I thought it might also be the mass air flow sensor, I bought some carb cleaner and sprayed through it while moving the plunger, didn't seem to make much a difference...
I thought it might also be the mass air flow sensor, I bought some carb cleaner and sprayed through it while moving the plunger, didn't seem to make much a difference...
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08-21-06, 12:13 AM
#8
the fuel pressure regulator is always the last component in the fuel system before the low pressure return to tank.
When removing emissions (and bacv) it is easy to forget to plug the hole left in the intake duct that used to feed the bac valve. A big vacuum leak would fit your problem exactly. Check the air intake tube and the brake booster vacuum hose. Any chance you didnt get the lower fuel injectors seated/sealed 100% in the holes in the block?
When removing emissions (and bacv) it is easy to forget to plug the hole left in the intake duct that used to feed the bac valve. A big vacuum leak would fit your problem exactly. Check the air intake tube and the brake booster vacuum hose. Any chance you didnt get the lower fuel injectors seated/sealed 100% in the holes in the block?
08-21-06, 10:40 PM
#9
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BAC is still installed, so that is ruled out. Car simply runs at a higher rpm for the 5 seconds (and is easier to start) with the BAC plugged in than not.
I will check the lower fuel rail and verify the injectors are seated properly, though I don;t see how that could cause no fuel in the return line.
The fuel in-line is connected to the lower fuel rail, then upper. Just in the event it is backwards (no reason it should be), I will swap them tonight, just to try it.
I'm thinking that it is a build up of pressure on the fuel rail though, as there is no fuel in the return lines.
I will check the lower fuel rail and verify the injectors are seated properly, though I don;t see how that could cause no fuel in the return line.
The fuel in-line is connected to the lower fuel rail, then upper. Just in the event it is backwards (no reason it should be), I will swap them tonight, just to try it.
I'm thinking that it is a build up of pressure on the fuel rail though, as there is no fuel in the return lines.
08-22-06, 01:38 AM
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Trace the line from the FPR. It should not go to the fuel filter. If it does, your lines are reversed.
If they are not reversed, it is likely that your FPR is stuck for some reason. Why a stuck FPR just because you rebuilt the motor? Sometimes old parts die when not being used, like my water pump when I had my rotary apart for its rebuild years ago.
If they are not reversed, it is likely that your FPR is stuck for some reason. Why a stuck FPR just because you rebuilt the motor? Sometimes old parts die when not being used, like my water pump when I had my rotary apart for its rebuild years ago.
08-23-06, 12:31 PM
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Heres what I have done:
Removed manifolds for the 7th time...
hecked the fuel rail for obvious malfuntions/mis alignment, none found.
Used compressed air to test the FPR. With the tank at 90psi, air was whistling through the FPR into the return nipple-- as though it was working properly-- who knows what PSI it was relieving at though.
Reinstalled manifolds, fuel lines. Started, ran for 5 seconds and died. Return line still completely dry.
Reversed fuel lines, absolutely no start, no fuel to injectors.
Reversed fuel lines again, starts and runs for 5 seconds, no fuel in return line.
Bypassed fuel filter to verify its not clogged, car starts runs 5 seconds, dies. return line still dry.
Start again, hold the cone of the **AFM** in about 1cm, engine stays running, but exhaust burns the eyes (assumine too rich or too lean)-- too rich if its getting too much fuel pressure.
Let the cone back to where it sits naturally with the vacuum and it stalls out second later.
So, either its not getting enough fuel pressure to relieve back to the return line (hard to believe considering the amount of fuel that sprays everywhere when disconnecting the in line.
or FPR is locked and not relieving, fuel line builds up so much pressure that the injectors flood the engine under normal duty opperation.
or... it still has something to do with the AFM, or both.
I'm planning on locating an adjustable FPR to install so that I can easily plumb a gauge and adjust to stock pressure. I figure this will be easier then attempting to locate and ship in a used fuel rail.
Is there the possibility of eletrical issues? For example, stalls when comes off the ECU start map and checks AFM for idle map?
Any suggestions anyone?
Removed manifolds for the 7th time...
hecked the fuel rail for obvious malfuntions/mis alignment, none found.
Used compressed air to test the FPR. With the tank at 90psi, air was whistling through the FPR into the return nipple-- as though it was working properly-- who knows what PSI it was relieving at though.
Reinstalled manifolds, fuel lines. Started, ran for 5 seconds and died. Return line still completely dry.
Reversed fuel lines, absolutely no start, no fuel to injectors.
Reversed fuel lines again, starts and runs for 5 seconds, no fuel in return line.
Bypassed fuel filter to verify its not clogged, car starts runs 5 seconds, dies. return line still dry.
Start again, hold the cone of the **AFM** in about 1cm, engine stays running, but exhaust burns the eyes (assumine too rich or too lean)-- too rich if its getting too much fuel pressure.
Let the cone back to where it sits naturally with the vacuum and it stalls out second later.
So, either its not getting enough fuel pressure to relieve back to the return line (hard to believe considering the amount of fuel that sprays everywhere when disconnecting the in line.
or FPR is locked and not relieving, fuel line builds up so much pressure that the injectors flood the engine under normal duty opperation.
or... it still has something to do with the AFM, or both.
I'm planning on locating an adjustable FPR to install so that I can easily plumb a gauge and adjust to stock pressure. I figure this will be easier then attempting to locate and ship in a used fuel rail.
Is there the possibility of eletrical issues? For example, stalls when comes off the ECU start map and checks AFM for idle map?
Any suggestions anyone?
08-23-06, 08:31 PM
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How would the dry fuel return line be explained by the AFM being faulty?
Unless it is not unusual to have no fuel in the return line in 5-10 seconds of the engine running? When would you expect fuel to relieve into the return line?
Unless it is not unusual to have no fuel in the return line in 5-10 seconds of the engine running? When would you expect fuel to relieve into the return line?
08-23-06, 11:39 PM
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In the need to get this running ASAP, I have purchased one of the inexpensive FPR's from ebay that are adjustable. In the event that the stock FPR is malfunctioning. Hopefuly this will eliminate my doubts and I will see fuel return in the return line as it should.
I am also looking into finding a replacement AFM incase that is also faulty.
Suggestions?
I am also looking into finding a replacement AFM incase that is also faulty.
Suggestions?
08-23-06, 11:56 PM
#20
ok
when you turn the key to ACC2 the fuel pump will prime for a few seconds, this gives you about 30ish or so fuel pressure, not enough to be forced past the regulator into the return line most of the time. the pressure is static so it will be there when you go to crank the engine, when the engine starts it depletes the pressure until the engine stalls from a lean condition.
now you said you can keep the engine running by holding the cone correct? well this tells me there is a large vacuum leak in the system somewhere, now you just need to find where.
general places for large leaks are at the 2 large vacuum lines to the main intake hose from the AFM, other places are at the bypass air control valve and also at the brake booster line at the manifold. other possibilites would be several vacuum lines disconnected, 1 usually isn't quite enough to bypass the AFM but several could.
when you turn the key to ACC2 the fuel pump will prime for a few seconds, this gives you about 30ish or so fuel pressure, not enough to be forced past the regulator into the return line most of the time. the pressure is static so it will be there when you go to crank the engine, when the engine starts it depletes the pressure until the engine stalls from a lean condition.
now you said you can keep the engine running by holding the cone correct? well this tells me there is a large vacuum leak in the system somewhere, now you just need to find where.
general places for large leaks are at the 2 large vacuum lines to the main intake hose from the AFM, other places are at the bypass air control valve and also at the brake booster line at the manifold. other possibilites would be several vacuum lines disconnected, 1 usually isn't quite enough to bypass the AFM but several could.
Last edited by RotaryEvolution; 08-23-06 at 11:59 PM.
08-24-06, 01:45 AM
#21
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So no fuel in the return line could actually be normal for this condition?
To test, I could ground the fuel prime jumper and I should see fuel in the return line, correct?
As for the vac leaks, I've been through the manifolds so many times that I can't see how there could be any vac leaks, or at least any of a sufficient amount to cause this much trouble.
That said... I felt it was a vac leak from the get go, that was my first instinct when it stalled out after a few seconds. Just don't see how that could still be it after going through the system so many times.
But if there really should not be fuel in the return line, that only leaves two possibilities: AFM and vac leaks...
Any easy way to locate vac leaks?
To test, I could ground the fuel prime jumper and I should see fuel in the return line, correct?
As for the vac leaks, I've been through the manifolds so many times that I can't see how there could be any vac leaks, or at least any of a sufficient amount to cause this much trouble.
That said... I felt it was a vac leak from the get go, that was my first instinct when it stalled out after a few seconds. Just don't see how that could still be it after going through the system so many times.
But if there really should not be fuel in the return line, that only leaves two possibilities: AFM and vac leaks...
Any easy way to locate vac leaks?
08-24-06, 02:05 AM
#22
the jumper should turn the pump on continuously with the key in the run position if the circuit opening relay is operating as it should, if not then you should start testing that relay circuit.
what you can also do is wire up a temporary positive feed directly to the pump(larger gauge wire black with a white tracer at the pump module) and see how it runs, if it stumbles this should give you an idea there is a vacuum leak and you can test for it with carburetor cleaner or a propane torch that is not lit.
what you can also do is wire up a temporary positive feed directly to the pump(larger gauge wire black with a white tracer at the pump module) and see how it runs, if it stumbles this should give you an idea there is a vacuum leak and you can test for it with carburetor cleaner or a propane torch that is not lit.