Intermittent stumble and shutoff. Codes 14, 24, 31.

[appleburger]

A new intermittent issue has popped up on my ‘94 that I could use some help with. I’m going to try to provide as much info as I can. Thanks to anyone that will read all this.

It started out of the blue one day when I was idling for about 15 minutes. There was a little stutter in the rpm and then it just died. Had been driving perfectly fine up until then. It restarted and immediately died. About 3 times. Then it started and drove fine for a weeks. No CEL.

Then about 2 weeks later after driving 500 miles on the highway, running around all weekend on and off road, it did the same thing cruising 75mph on the highway. Got it restarted and it died again a few miles down the road.

I was already suspecting it was ambient temp related when it happened idling on a hot day. I thought so even more on the highway as local temps neared 100*.

Thankfully, when it happened on the highway it tripped the CEL. 14 (ignition signal), 24 (air temp sensor), & 31 (VAF). Still suspecting heat I insulated the wiring harness with what I had on hand (beer cans from the camping trash) along the firewall and to the VAF and zip tied it as far away from the exhaust as possible. It made it the remaining 400 miles home without issue and was fine for another week or so.

Then it did it on cold start on a day where ambient temps were below 90. Heat theory went out the window. I was still able to get it to start and drive 25 miles home where I parked it and started to get more serious about diagnosing.

Based on a bunch of pre-existing threads and wanting to do some maintenance anyway I’ve since replaced plugs, wires, cap, rotor, ignition coil, VAF with a known good used, cut the loom from the VAF wiring harness to inspect for exposed wires before re-wrapping with cloth tape and high temp aluminum tape (including the main harness along the firewall).

Drove it for an hour last night and it was running like a champ. Then it just died on my about 10 times on my way home from work. Still throwing codes 14, 24, & 31.

I’m going out now to triple check the intake tube from VAF to TB although I’ve been thorough in my last checks and have a new one in the mail already. I don’t know what else to do at this point.
This thread is what lead me to suspecting the VAF:
**SOLVED** Codes 24 & 31 on 1994 FZJ - https://forum.ih8mud.com/threads/solved-codes-24-31-on-1994-fzj.1258070/page-2

 

[appleburger]

Just disconnected the battery for 30min, removed and inspected the intake tube for cracks, and cleaned & reattached all engine grounds. Started and died after about 30 seconds. Only giving code 14 now. Removed and inspected igniter and wiring. Cleaned bracket ground and reinstalled. Died and gave code 14 again.

Ordered used igniter. Any other ideas?

 

[appleburger]

Popped a used OEM igniter in. Idled for 45 minutes then died. Throwing code 14 still.

Another bit of info that I'm learning might be related is that my tachometer has lost signal a couple of times but only momentarily and did not coincide with any problems running. The needle just bounced a few times while cruising. Looking at the ignition circuit and noticed the igniter is what supplies the tach signal.

Getting pretty fed up chasing this down.

 

[jonheld]

Popped a used OEM igniter in. Idled for 45 minutes then died. Throwing code 14 still.

Another bit of info that I'm learning might be related is that my tachometer has lost signal a couple of times but only momentarily and did not coincide with any problems running. The needle just bounced a few times while cruising. Looking at the ignition circuit and noticed the igniter is what supplies the tach signal.

Getting pretty fed up chasing this down.

Igniters do fail. They can become intermittent or just die altogether.
When the engine stalls, does the CEL remain illuminated?
Are you sure the igniter you installed was a good unit?
Have you reseated ECU connectors?
Have you checked the ECU harness where it runs along the lower metal frame under the glovebox?
Have you verified continuity between the igniter and ECU?

 

[appleburger]

Igniters do fail. They can become intermittent or just die altogether.
When the engine stalls, does the CEL remain illuminated?
Are you sure the igniter you installed was a good unit?
Have you reseated ECU connectors?
Have you checked the ECU harness where it runs along the lower metal frame under the glovebox?
Have you verified continuity between the igniter and ECU?

Thanks for the ideas!

When the engine stalls, the CEL stays illuminated until I get it to restart. Then it goes off. Once its running correctly the CEL goes off and stays off until it stalls again.

I can't be 100% certain this igniter is good but the person I bought it from stated it was and it seems like the probability of having two igniters with the same exact intermittent problem is very low. Certainly could happen. From what I've found there isn't a way to bench test the igniter.

I did just go remove the ECU, cleaned all pins and connectors (they all looked pristine), and reseated all the connectors. While I was doing this I verified there is continuity between the Ignitor plug and ECU plug. I wiggled the harness around while checking continuity to see if it was lost. Since the issue is intermittent its hard to know.

I have inspected all the harness I can access and don't see any signs of wear.

I also just disconnected the fusible links to inspect and clean.

I have it idling right now to see if reseating all these connectors made any difference. Fingers crossed but my expectations are low.

Ordered a new EFI relay and fusible link just in case.

 

[appleburger]

Doing as much reading on this issue as I can and thinking of other things that could be related symptoms. Since idling yesterday for 1.5hrs I drove it to work today and it didn't die. I did notice a slight rhythmic hesitation but it was much slower than any single injector or plug firing. I'd say maybe 1-2 times a second. I don't see any change in RPM and if I weren't paying real close attention it would be easy to miss the "hesitation".

I have started noticing a gas smell after turning the car off and getting out. It lingers for a good bit. I can go inside, come out 30min later and still smell it. No visual signs of a leak. Gas cap is tight and looks in good condition. I've come to understand that the IGF signal is measuring continuity through each spark plug when it successfully fires and therefore completes a circuit. Is there a possibility that a fuel related issue like a stuck injector causes a plug not to fire and therefore throws code 14 and cuts spark?

Am I barking up the wrong tree in desperation or do you think this is this worth pursuing further? I've replaced every component in the ignition system and verified continuity in the harness connect it to the ECU.

 

[ZackR]

When you were digging into the wiring harness did you happen to check the area where it passes the EGR pipe? That's a common area for hidden wiring shorts that cause all kinds of issues from misfires to poor running (and hesitation) without triggering the CEL. I lived through this myself for quite some time several years ago and it was difficult to diagnose.

Continuity may be good during the test but may change when the engine is running due to vibration and heat.

 

[ToyotaDon]

I've come to understand that the IGF signal is measuring continuity through each spark plug when it successfully fires and therefore completes a circuit. Is there a possibility that a fuel related issue like a stuck injector causes a plug not to fire and therefore throws code 14 and cuts spark?

Am I barking up the wrong tree in desperation or do you think this is this worth pursuing further? I've replaced every component in the ignition system and verified continuity in the harness connect it to the ECU.

What you are describing is an ion-sensing ignition system, which has been used on some vehicles for timing control and misfire detection. My understanding is this system would only be found on vehicles with coil-on-plug type ignitions. The igniter and distributor on the 80-series is just not that technologically advanced. The IGF signal is simply the igniter giving "feedback" to the ECM that it fired the coil.

You'll want to also check the other circuits at the igniter (I did not see where you said this was done) and possibly prepare to buy a completely new igniter. If you have the FSM, some of the information for the Ignition System On-vehicle Inspection could be helpful when the problem is occurring. Just don't get off on rabbit trails of things which would not cause the problem (focus on igniter wiring).

 

[appleburger]

What you are describing is an ion-sensing ignition system, which has been used on some vehicles for timing control and misfire detection. My understanding is this system would only be found on vehicles with coil-on-plug type ignitions. The igniter and distributor on the 80-series is just not that technologically advanced. The IGF signal is simply the igniter giving "feedback" to the ECM that it fired the coil.

You'll want to also check the other circuits at the igniter (I did not see where you said this was done) and possibly prepare to buy a completely new igniter. If you have the FSM, some of the information for the Ignition System On-vehicle Inspection could be helpful when the problem is occurring. Just don't get off on rabbit trails of things which would not cause the problem (focus on igniter wiring).

Thanks for this! And this is why I consulted before diving into a fueling rabbit hole.

 

[jonheld]

I have started noticing a gas smell after turning the car off and getting out.

Is the charcoal canister clogged?
Are the hoses to/from the canister in good condition?
Do you get pressure release when removing the gas cap after driving?

 

[appleburger]

The saga continues. Thanks for all your advice so far! First an update.

Since my last post I replaced:
- fusible link (OEM)
- intake tube (OEM)
- EFI relay (OEM)
- charcoal canister (Duralast VC120)

I thought I had it fixed. Ran great for a bit. Took it on a 500 mile road trip. Started doing the slight, rhythmic hesitating at highways speeds again but never stalled, never had trouble starting, and no CEL. Then a few days after we got home it would crank but not start. It has not run since then.

On this trip my power brakes started losing pressure at idle as well making me suspect a vacuum leak. Smoke test showed part of EGR was leaking so I disable/blocked it. No vacuum leaks now.

Since it stopped running I've replaced:
- fuel filter (OEM)
- fuel lines associated with filter (OEM)
- fuel pressure regulator (OEM)
- EGR disable/block (Hudd Expo)

Still cranking but not even trying to fire. No CEL. As soon as I have another set of hands I'll test spark at the wires. I also plan to inspect the wiring at the fuel pump and I have an OEM pump sock and gasket standing by. At this point I feel like the only major component in the entire EFI system I haven't replaced is the pump.

List of other parts I've replaced for anyone coming in new and might have ideas:
- plugs (NGK BKR5EYA)
- plug wires (NGK 4413-TE68)
- dist. cap (OEM)
- rotor (OEM)
- MAF (OEM used)
- Igniter (OEM used)
- reseated and cleaned ECU connector, verified continuity between ignitor and ECU
- CEL is gone, codes went away at different times leading me to believe my original issues were multi-causal and some have been remedied

I have to admit that my troubleshooting hasn't been as methodical as I would like. But its a new-to-me vehicle so I've definitely been in a "it-probably-needs-replaced-anyway and while-I'm-in-there" mindset.

 

[appleburger]

I’m such an idiot. I disconnected the fuel pump connector under the chassis to do the fuel filter weeks ago and just finished the job today. It dawned on me minutes after making the update. That’s what I get for being down for so long.

I’m back up and running! Haven’t taken it in the highway yet.

 

[sogafarm]

The saga continues. Thanks for all your advice so far! First an update.

Since my last post I replaced:
- fusible link (OEM)
- intake tube (OEM)
- EFI relay (OEM)
- charcoal canister (Duralast VC120)

I thought I had it fixed. Ran great for a bit. Took it on a 500 mile road trip. Started doing the slight, rhythmic hesitating at highways speeds again but never stalled, never had trouble starting, and no CEL. Then a few days after we got home it would crank but not start. It has not run since then.

On this trip my power brakes started losing pressure at idle as well making me suspect a vacuum leak. Smoke test showed part of EGR was leaking so I disable/blocked it. No vacuum leaks now.

Since it stopped running I've replaced:
- fuel filter (OEM)
- fuel lines associated with filter (OEM)
- fuel pressure regulator (OEM)
- EGR disable/block (Hudd Expo)

Still cranking but not even trying to fire. No CEL. As soon as I have another set of hands I'll test spark at the wires. I also plan to inspect the wiring at the fuel pump and I have an OEM pump sock and gasket standing by. At this point I feel like the only major component in the entire EFI system I haven't replaced is the pump.

List of other parts I've replaced for anyone coming in new and might have ideas:
- plugs (NGK BKR5EYA)
- plug wires (NGK 4413-TE68)
- dist. cap (OEM)
- rotor (OEM)
- MAF (OEM used)
- Igniter (OEM used)
- reseated and cleaned ECU connector, verified continuity between ignitor and ECU
- CEL is gone, codes went away at different times leading me to believe my original issues were multi-causal and some have been remedied

Check the vacuum valve on the brake booster for leaks for the brakes. City racer has a good reasonably priced brake booster if you need.

 

[sogafarm]

I’m such an idiot. I disconnected the fuel pump connector to do the fuel filter. It dawned on my minutes after making the update. That’s what get for being down for so long.

I’m back up and running! Haven’t taken it in the highway yet.

Nice easy fix!

 

[appleburger]

I keep coming back mainly to add details in case someone else has these issues.

The momentary, cyclical hesitation at highway speed was still there. Here's what my fuel pump sock/filter looked like when I pulled it. New sock going on. I could imagine a scenario where a flap was getting sucked to the intake hole, causing fuel pressure to dip, reduced fuel pressure released the flap, and it repeated again and again. We'll see.