HammerDown6

I've recently developed an interesting problem. It seems as if my engine is shutting itself off from time to time while I'm driving. What happens is, the CEL comes on, and the RPMs drop significantly. A fraction of a second later, the vehicle lurches, the RPMs come back up, and the CEL goes off. I should add that it will do this at any speed and in all gears. I'm thinking that the engine loses its ignition signal, but, since the vehicle in gear, moving, and the key is on, that it's able to restart itself - just as if you were push-starting it due to a dead battery. If you've ever had to push-start a vehicle, you're familiar with that lurch when the engine catches, and that's exactly what it feels like. Any thoughts on what might be killing the ignition signal? TIA.

'91 4Runner
3.0, 5spd

CMD93

That was the engine that I had in my old Nissan Maxima.

HammerDown6

Whoops, thanks for catching that one - I have a Pathfinder too.

It is the 3VZE.

MTL_4runner

Maybe the alternator is on its last legs?

Duffdog

well---my 89 22re did the same thing your describing, someone said to make sure that the wiring harness is not rubbed through on the intake manifold....did that, didnt work. the real problem was one of the cam lobes was worn flat and one of the cylinders would work against the engine only once in a while....changed the cam, hasnt stalled once since then...

maybe that could be your prob

T

amusement

Replace your TWO relays >> Fuel injector relay next to the fuses and the other relay under the key switch (Dash). It will fix ALL.

HammerDown6

I doubt it's the camshaft. A bad cam lobe won't give you an intermittent problem. If it's flat, it's flat. The problem will be present on each rotation. This will cause the valve to start to float as RPMs increase, and get progresively worse. This motor will throttle up to 5K no problem. Plus. I'm still getting really good gas mileage, and power/response hasn't changed.

Do I detect a note of sarcasm here, or are you being serious? That would certainly be an easy fix. How can you be sure?

Thanks guys.

amusement

Do I detect a note of sarcasm here, or are you being serious? That would certainly be an easy fix. How can you be sure?
-- HammerDown6

Yes, it's that easy! Worked for me.

So, what are you waiting for? That's sarcasm.

Nam

I would check all connections tight to the ECU, igniter, and fuel systems.

Also, let it idle and see if the problem happens.

this problem is hard to solve...but good luck!

Nam

HammerDown6

I will double check all my connection. This problem has never occured while idling - happens only when I'm rolling.

As to the relays, one iis in the engine bay by the check connector, correct? And is the other one behind the driver's kick panel or by the main fuse block? Thanks.

MTL_4runner

The intermittent nature does certainly sound electrical (ie not a cam lobe).
Check all the grounds especially, that will cause the EFI to die like that as well.

TexJJ

Hammerdown, I too have a '91 withthe exact same problem. Did you ever resolve it? I hate that I am pretty confident in the motor until the lurch hits.

HammerDown6

Boy, it's been a while now since this was an issue for me. IIRC, the problem ended up being a faulty ignition coil. Once replaced, the problem has never presented again, and she's been running like a champ. I believe that I had been tracing spark when I noticed that my poor man's tester was showing intermittent and inconsistant spark/voltage at the coil. I remeber it taking a long time to nail down. Good luck.

TexJJ

Thanks,

I already replaced that bad boy, now trying our hand at the EFI relay. These electrical problems are just no fun. If no go there, we will try a new MAF.

Gadget

I think you have diagnosed your problem already.

If when this happens the tach falls off much faster then the engine is slowing down, then that usually indicates an ignition problem. If the check engine light comes on and is lit while this is happening, that is a good sign. That tells you the ECU has power and on Toyotas normally the main EFI relay powers everything that makes the engine run.

The tach normally gets its signal from the ignition module which Toyota calls the igniter. I am not up to speed on your engine speciifically, but all this should generally apply.

I would start my diagnosis with the ignitor and the wire harness leading to it.

Another approach which is always a good one is to use the factory service manual and look in the diagnostic by symptom section and pick the one that most closely discribes what you are experiencing and then follow that diagnostic tree without skipping a step and that should lead you to the problem in short order.

Got a heat gun???

Gadget

Weasy2k

did you check the code at all?

TexJJ

We have not checked for a code as the check engine light never comes on. My understanding (limited I admit) is that no code is saved unless the CEL comes on.

The MAF reads within spec. We have changed the ignitor and coil, and today changed out the EFI relay.

This problem is is spurratic; we have to drive quite a few miles to find another fault condition (i.e., 300-500 miles.) Tomorrow I leave back to my place and will log about 350 miles so we will see. Before I do however, I will try to jumper for the engine codes to see what happens.

Any more ideas. I love/hate this problem solving which is now going on for 6 months.

JJ

TexJJ

Well NEWS and other questions:

I figured (INCORRECTLY) that since the check engine light never showed, no errors were being recorded. I was wrong, we jumpered the diagnosis module and got not one but TWO error codes, EC 24, and EC 31.

My Haynes guide lists:

EC 24 Intake Air Temperature Signal - Open or short in intake air temperature sensor signal (THA)

EC 31 Air Flow Meter Signal or Vacuum Switch Signal - Open circuit in Vc signal or short circuit between Vc and E2 when idle contacts are closed. Open or short in vacuum switches

So I am on the track to thinking it is the MAF. Now the engine had been sitting for about 5 hours so was cold. The Haynes guide says to run the diagnosis at normal operating temperatures with engine off. Does that mean I need to run the motor to warm it up before I take the reading? I think that the error codes are logged at the fault not when I run the diagnosis.

So any other ideas before I buy a MAF. It is the damnest thing because we are getting spec resistance when we test it.

JJ

Weasy2k

lol i was just ognna post saying "yea it does " the OBD-I ecu only stays on when something is occuring all the time...but since this is intermitent it will just flash and save.

That would be the AFM right there...
ignor the haynes manuel those readings where taken when the problem started and check all the wiring to make sure there is no cuts in any of it!

TexJJ

CORRECTION I AM AN IDIOT!

So while diagnosing yesterday we failed to rehook up the MAF when we started the car. Needless to say it did not start. We plugged it back in and went on our way. That was the error code I read.

So today I put on about 300 miles straight on it. Around 180 miles in, it jerked/stumbled not really sure how to describe it. No CEL, no codes (I pulled over to check.) I have a new EFI Relay. I am at a loss where else to check. Since no CEL or code, I am assuming that the ECU is cutting off during the stumble. The other electricals stay on.

It is so damn irregular. Usually just crusing along and boom a stutter. Any other ideas?

JJ