starts great. runs for a few seconds. dies

[yellowrunner]

I recently installed a 7mge in my 1985 4runner. The problem is that it will start strong every time, then run for a few seconds at a high idle then die. There are no codes since the ecm won't send them for what ever reason (I followed the diagnosis and the tsrm says that the computer is bad).

This is all very frustrating to me because I made sure the engine was running great before pulling it from the supra, I changed the spark plugs while the engine was hanging and now it doesn't run?

While trying to diagnose the problem I have:
Checked the voltages from the ecm they all are within spec.
Checked afm and tps resistance=good
Made sure that intake, all 3 cam covers, throttle body, cold start injector, IAC, and PCV hoses are all sealed.

If I hold the afm flapper open slightly then the engine will continue to run.
If I hit the throttle the engine will die instantly.


There is a small vacuum leak somewhere though I can't for the life of me find it. It also doesn't seem to me that a small vacuum leak would cause this problem. I'm working on getting a new ecm but in the mean time I would like to keep working on the problem because I don't really think it is a problem with the computer.

Do you guys have any more ideas for me to try?

Thank you

 

[benchwarmer]

Sounds to me like your IAC is not working.

 

[yellowrunner]

That would make sense. However that was the part that I repaired while the motor was still in the car. It was sticking, causing the motor to rev up and down, so I took it apart, unseized and oiled it. It seems to still make the noise when the motor shuts off and it clicks when I reset it by jumping TE1 E1, could it still be malfunctioning somehow? Oh, and the ECM terminals read the correct voltages for the ISC.

I keep wondering if the AFM could have some sort of problem that the resistance test wouldn't show?

 

[ForcedTorque]

I was going to guess (shouldn't be done in tech) AFM. Are you sure the vacuum under the accordion is connected to the idle up at the back of the power steering pump?

 

[yellowrunner]

Idle up on the power steering? I'm using the pump off of the 4runner so I plugged the vacuum line from the power steering pump and also the one from the accordion, should I not have done this?

 

[CRE]

Where is the air for the idle speed control valve coming from?

EDIT: The reason I ask is because the GE's ISC has to pull air from behind the AFM in order to move the vane far enough to close the FC switch. The FC switch cuts power to the fuel pump when the vane is closed.

 

[935motorsports]

If the ISC was not working, the engine would still idle when you hold the throttle partially open.

If the engine runs great for a few seconds then dies, it could be related to the fuel pump resistor. I'm not sure if the truck has that, but do check it out. It is often missed during swaps.

 

[CRE]

I wasn't questioning if the ISC was working... I was questioning if it was placed where it would move the vane in order to close FC... I thought that was rather clear.

The whole thing dying if he steps at all on the throttle gets me, but it's easy enough to test if part of this is a pump issue... jumper FP and B+ in the diagnostic block. That'll bypass the fuel pump relay/resistor and the FC switch.

 

[yellowrunner]

You could have something with the ISC hose. Correct me if I'm wrong, but in order for the isc to pull the flapper far enough open it must have another source of air pulling from the accordion hose? I assume this is what the hole on the bottom of the accordion was used for as well as the metal vacuum line that runs across the front of the block? So by blocking off the hole on the bottom of the accordion and plugging the line I am not allowing the engine to pull the AFM flapper far enough open?

As for the fuel resistor system I currently have the 4runner controlling the fuel pump with the ignition, not ideal or safe in the long run but I figured I would fix it later so the fuel pump turned off when the motor died (like in a bad wreck). I don't think it could be the fuel system unless the ECM has a way to shut off the injectors if it detects a problem with the engine.

 

[CRE]

I thought there was only the hose for the PS which connected to the accordion.

The fuel pump resistor and relay do not cut power to the fuel pump under any circumstance... well, unless they're broken. The fuel cut off is in the AFM, that's he FC switch; Have you bypassed that?

Like I said though, easy enough to test... jumper the fuel pump, and disconnect the ISC from the intake piping so its airflow is unobstructed.

The engine isn't just dying at idle though, right? Well, one thing at a time I guess.

 

[hvyman]

the isc should make a clicking noise after the engine is shut off(its in the tsrm). (to drunk to read the rest of the thread sorry).

 

[yellowrunner]

Jumping the fuel pump doesn't seem to make any difference. I was looking at the tsrm wiring diagrams and that would make sense I have actually bypassed the FC terminal of the AFM etc...

Is it possible for an AFM to be bad and still check out okay with the resistance specs in the tsrm? Mine checks out okay (several times) and the wires to the ECM have continuity.

Also same thing with the TPS its wires have continuity and the terminals resistance is within specs. But I noticed if I disconnect the TPS and start the motor it will run almost twice as long before dying out. Though if I hit the throttle it will still die instantly.

It appears that the only thing that makes it run longer is by propping the AFM open just a bit. So even though it seems good I still question it.

 

[AJ'S 88NA]

I see you said you checked the TPS, have you set it according to the TSRM?

I guess it is possible for it to be bad and still check OK.

 

[CRE]

The only part of the TPS you really need to be concerned about is the IDL switch. With the AFM, yes it could measure the proper resistances and still be bad. With the ignition 'on' but the car not running measure the voltage at Vs while you slowly move the vane through its full sweep. The scale should be relatively smooth and steady; Look for flat spots, spikes and drops.

 

[yellowrunner]

AFM checks out with a perfect smooth sweep through 3.91 to .43 V

 

[yellowrunner]

Problem Solved, it was indeed a fuel pump signal problem. It is amazing how long an engine can run without the fuel pump on, running on only the residual pressure from cranking over.

thank you for your assistance

 

[CRE]

Mind being more descriptive? I'm curious.

 

[yellowrunner]

I didn't have the fuel pump wired correctly, the pump would turn on only while cranking once the key was let off the pump would quit. What threw me off was how long the engine would run without more fuel I got it to run for almost 30 seconds earlier today. I wouldn't have guessed that was possible, though it definitely explains the immediate dying of the engine if any throttle was applied.

To fix the problem I grounded the FC wire at the B1 connector and then spliced the ground from the AFM ,whose other end is on the C1 connector on the other side of the engine (this connector isn't used in my swap), to the FC wire from the 22re AFM. The AFM on this engine stays with the truck unlike the 7mge which goes with the motor.

This should provide a stock operating fuel system that will shut down in the event of a crash.

Still no check engine light when the key is on though? Hopefully a different ecm will help with that.