1992 electric/ignition issue

[Flyer88]

1992 3ZVE M/T

Out of the blue one day..... truck won't start. With the key ON, I got no CEL (check engine light). Starter turns, strong, no ignition. Checked plug wires, coil, secondary, distributor, all resistance values within shop manual specs. Checked ECU, wiring, CEL bulb (to ground, illuminates). Fuel pump good, pressure at rail during start. Spark check bad- no spark. CEL will not throw a code, (not even steady blink) since light won't ever come on.

After a few days troubleshooting stuff, the CEL decided to illuminate with the key ON, and then bingo, truck started fine, ran fine. Checked for codes, got steady flash (no codes). Had no problems for a few weeks, and then....

Drove to grocery store, no trouble. Came back out, tried to start truck, no CEL with key ON. Cranked engine, turned over for 1-2 seconds, CEL illuminated during cranking, engine started, ran rough. CEL stayed lit. Engine ran as if not all cylinders were firing-- hesitated during acceleration, wouldn't produce much power, ran very rough. Drove the short distance home, marginally.

Currently, the truck will give the CEL before start normally with key ON about half the time I try to start it. When it does, it starts and runs fine, CEL goes out after start. The other half of the time, I get no CEL with key ON, but sometimes it comes on halfway through cranking and engine will start, but runs rough and CEL stays lit. I can't get the CEL to give any codes in any case- it either doesn't work, of gives steady no-trouble flash.

I have checked (per shop manual) and tried unplugging airflow sensor, throttle position sensor, cold start injector, and oxygen sensor. Nothing changes.

I'm guessing I have either an intermittently bad ECU or ignition module, or bad wiring (although I have checked all I can think of for open/short). There's no check for the ignition module. Has anyone experienced this before?

Other than a bad ECU, what can cause the CEL to NOT come on with key ON prior to start? Does the ECU "talk" to the ignition module prior to cranking? Can a "bad response" from the ignition module prior to start cause the CEL to stay off prior to start? Then, maybe during cranking, a few "good" responses come from the ignition module and the CEL comes on? Am I on the right track?

I'm trying to figure out what part to spend money on first, if it's not a wiring issue.

 

[Camokid84]

This is a shot in the dark based off what you said, so dont quote me on this but I think you might have something going on with your knock sensor. Since it advances and re****s timing, your knock sensor might be on the fritz sending your whole ignition system into a fritz. Just a thought, maybe a path to start looking. And if I am not mistaken, the reason why its throwing the CEL and weird times is that since its an OBD-1 I think it will only show a code if it is happening currently. So if everything looks fine it wont come on, but if something twiches out like a knock sensor it will throw the code. OBD-1 systems can be hard to predict.

 

[Flyer88]

I will look into the knock sensor..... but would it cause the CEL to NOT come on with the key ON before start?

 

[Camokid84]

It very well could, like I said OBD-1 systems are hard to predict. If the knock sensor it working sometimes, or isnt quite out of limits the cpu wont read it as a fault. Let me know what you find though, I am letting my schooling and time a Toyota dealership as a technician guide me, although I am fairly new to diagnosis.

 

[pkinfinity]

Ignition Oddity

My 89 4runner had other strange starting problems. The 4runner will start nicely. But after driving and getting hot, it would not turn over. After it would cool a bit, the 4runner would start up again and run as strong as usual.

Over the years I have replaced the battery several times, replaced the starter, replaced the spark pluck wires with heavier gauge wires, and rebuilt the ignition switch itself. The ignition switch rebuild seems to have fixed the problem mostly, but its still a little flaky. (It was not the best rebuild, the key can be removed sometiems without turning it off.)

 

[Flyer88]

Did more troubleshooting today....

I'm not a professional, but it seems that any sensor failure would not cause my problem of the CEL not coming on at all with the key ON before start. I have unplugged every sensor I can find, one at a time, and nothing changes.

The CEL is supposed to come on with the key ON before the engine is started. When cold, it comes on, MOSTLY starts nornally, drives fine.

After one start, if I shut it off and try to put the key ON again, there is no CEL before start. CEL will still come on halfway through cranking and start, but will run terrible, and the CEL stays on.

If I let it sit for a minute or two while off, then turn key ON, CEL mostly comes on like it should, and starts fine.

Seems to be time or occurance related somehow. This occurs even if engine is only run for a few seconds, before it heats up.

Been checking wires and grounds, found no trouble yet.

I know ECUs don't fail often, but maybe that's what I looking at? Any more ideas?

1992 3VZE M/T

Thnaks

 

[Flyer88]

I think I fixed it

Put new spark plugs in today. Hasn't had a problem since. My neighbor said bad plugs can cause RF interfernece and screw with the computer. Makes sense. That would explain why it would start once or twice before it would conk out. After it sat for a while, the ECU components would "forget" that RFI garbage and straighen itself out, like a slow bleed-off of voltage.

Hope that really did it. So far so good.

 

[Flyer88]

Problem is back...

Well, new plugs, wires, cap and rotor. Ran fine for a few months. Now, Running terrible again after start. CEL comes on, engine runs bad. Turn off engine, try to restart, no CEL with key on before cranking. It will turn over, then the CEL flickers to life, engine starts, runs terrible, with CEL on. Can't get any codes out of computer because CEL is off with key on before start. Help- any other ideas?

 

[77'911]

Just a thought, you might consider replacing the EFI relay if it has not been done. After having a long chat with a guy at the parts counter, this seeming is a strong source for automotive gremlins in older toyotas. They are fairly inexpensive through the dealer, thought I paid about $12. I would also go through the procedure in the factory manual and clear out the codes, then install the new relay.
regards