1989 Toyota 4Runner intermittant start/fail to start/runnin

TEXASJOHN

MEMBER
1989 TOYOTA 4RUNNER

Electrical problem
1989 Toyota 4Runner 6 cyl Four Wheel Drive 100k miles

vehicle starts and runs perfectly. Or it doesn't. Problem been going on for couple of weeks. 3.4L V6

Symptoms same now as when it started. These problem determination steps and possible solutions have been implemented:

By my mechanic, who returned the vehicle thinking it was fixed because it was running perfectly.
Cleaned battery terminals
replaced fuel filter
tested fuel pump pressure. It's OK
replaced spark plugs (driver side bank wet with fuel, other side not)
replaced oxygen sensor

I picked up vehicle, it started perfectly and ran about 60 miles. Stopped for night, didn't start next morning.
Next day I jumped it and it started up, ran rough for about a minute then smoothed out perfectly.

I replaced battery, it ran OK for another 60ish miles then it wouldn't start next morning. I replaced starter.

Still did not start. Starter clearly engages engine, fan and pulley rotate. Sound is not "normal". Sounds like there is no compression.

Took it back to mechanic on flatbed trailer. It would not start for him, same sound/symptoms. He replaced mass air flow sensor, rechecked timing belt and marked it to see if it was slipping. Not slipping
Compression tested OK. Still did not start. Left it overnight.

Started next morning but ran extremely rough for about 2 minutes, then smoothed out instantly. Shut it off and started it again. Very smooth, ran fine.
Mechanic does not believe that the real problem has been fixed and that it could fail again at any time. He has exhausted his problem determination capabilities and given up on the vehicle. Note. Have used him for over 15 years, he's honest, didn't charge me anything for his diagnostic efforts.

Left overnight it started again. Have driven it and started it for couple of days. Running fine and strong at present but am convinced it will die again.

Summary. Numerous reasonable "fixes" have had no affect on the symptoms although they were reasonable to do.

I suspect an electrical problem. What would cause these symptoms, given the analysis and fixes to date?

5 Replies

KHLOW2008

MECHANIC
41,814 POSTS

Hi texasjohn,

Thank you for the donation.

This being an intermittent problem is not going to be easy to diagnose.

From the symptoms I would say it is more likely to be a fault with the electrical or sparks.

When engine could not be started, you would need to check if sparks are present.
If the problem only occurs at cold starts, then the Engine Coolant Temperature sensor could be the cause.

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Sunday, May 9th, 2010 AT 2:37 PM

TEXASJOHN

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2 POSTS

Sparks? Do you mean spark plugs? They are new.

What, specifically, do you mean by sparks?

Would a failed engine temperature coolant sensor result in apparent loss of compression (starter/engine turning over sound is not same in failure mode as it is when engine turns over and starts properly) while not throwing any codes?

As I said in my initial post, "I suspect an electrical problem. What would cause these symptoms, given the analysis and fixes to date?"

I know it's not the usual starting problem, but I suspect it is a simple fix once we put a finger on it.

Thus, I'd appreciate a specific suggestion as to what to check.

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Monday, May 10th, 2010 AT 4:02 AM

KHLOW2008

MECHANIC
41,814 POSTS

Sorry if I did not make myself clear. Sparks means ignition sparks.

ECT would not cause compression losses, neither would any other electrical faults.

I would suggest testing the compression at cold engine. What are the compression pressures for both wet and dry tests?

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Monday, May 10th, 2010 AT 10:36 AM

4RUNNERRUSSELL

MEMBER
2 POSTS

I have had similar symptoms with my 1998 4Runner(SR5, 274K miles, 2WD)

When we 1st got the vehicle it would simply stop running at times, very intermittent and didn't happen very often. Sometimes while driving down the interstate, it would just stop running. Then it would restart right up. I could slam it into neutral and restart the engine on the fly, but now it does not restart right away. Now sometimes I have to let it sit for a few minutes making sure I have turned all of the electronics off (radio, ac) before attempting another restart. Seems to make a difference but I don't know if it really does.

Soon after purchase we got a recall notice in the mail for an ingition module, if memory serves me correctly. But never got it replaced. Now, I wish I had.

Hope this helps. Perhaps it is your eginition module also.

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Friday, May 21st, 2010 AT 12:04 PM

4RUNNERRUSSELL

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2 POSTS

Geesh, embarrassing. Couldn't seem to spell ignition, and twice.

If not ignition module then something to do with the ignition system. Starter module? Something like that?

Anyone who knows, please feel free to chime in.