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Chris (aka-Moose)
Chris (aka-Moose), Auto Technician
Category: Toyota
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Experience:  16 years of experience
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Corolla 4AFE: 1990 Toyota Corolla, 4AFE engine. The ignition

Customer Question

1990 Toyota Corolla, 4AFE engine. The ignition timing is extremely retarded, about 20 or more degrees. I cannot set the base timing by jumpering the test points, there isn't enough range on the distributor. I've checked the timing belt and cam timing, it's spot on. This problem has gotten progressively worse over a period of a few weeks. A new igniter and coil were installed, and then an entire new distributor was tried. There are no fault codes. I've now also tried a used ECU with exactly the same results.
Submitted: 1 year ago.
Category: Toyota
Expert:  Pavlin Koev replied 1 year ago.
Hi Good morning and Welcome to Just Answer! My name is XXXXX XXXXX I will do my best to help. Suspect Crankshaft woodruff key. if it is broken or missing gear to crank position will change. The way you describe the problem it looks like problem is there. Please check and let me know.Pavlin
Customer: replied 1 year ago.
Pavlin, thanks for your help. Here's some more info. First of all, I'm a mechanical engineer and former import and exotic auto tech, so you can talk to me at a professional level and I'll understand what you are saying, don't need a lot of explanation.

Regarding the car and the symptoms: The car belongs to a dear friend who is nearly indigent. The car is a wreck, and I keep it running for her at no cost and people think it's sort of miraculous that it's still on the road. The car was first brought to me about a month ago not running - no spark. After replacing the coil and igniter, I discovered the lower RPM pickup in the distributor had failed. Got a junkyard distro, found the lower pickup in that one also in the process of failing (same mode) and fixed it with epoxy. Swapped in the new igniter and coil. Car ran OK, though it had a bad stumble and hesitation on hard acceleration. My timing light was inop at the time, but I bumped the timing up by ear and the car ran well. That's the first clue that something was not right. With the original distributor, the car ran well until it failed. Car ran OK with the junkyard distributor and bumped timing for about a month, though I was still uneasy about the distributor repair I had made. About a week ago, she started to complain that the car wasn't starting easily and was not accelerating well. She brought the car to me, and it was FINE on a test drive. "Like when you go to the doctor..." she said. Then it suddenly got into this retarded timing mode, and she said "See!" Car's really not drivable this way at all.

I had already purchased a new aftermarket distributor and installed that, and the car still ran poorly -- no change. This distributor is now in the car, complete with the igniter and coil that came with the new distributor.

Got my timing light working, and confirmed that the timing is at least 20degrees retarded. It hasn't gotten better since that test drive, but the fact that it has deteriorated slowly and has also improved (briefly) suggests to me an electrical or electronic fault. That plus my confirmation that the cam timing is OK leads me to look at electrical issues.

I've read that the ECU will retard the timing when it senses an overheat condition AND the throttle is open, and advancing the timing when the throttle is closed. Perhaps this isn't consistent across all ECUs. The TPS is functioning, and does effect a change in engine operation when disconnected, however the timing does not advance when at closed throttle.

My thoughts:
ECU is reading a condition causing it to enter a limp-home, engine protective mode. What sensors might do this? Is this even a capability of the ECU?

A wiring fault. Bad grounds to ECU, bad connection to some sensor somewhere. (MAP sensor and TPS both work, haven't checked others.)

Incompatible igniter. Perhaps the original was an "oddball," and the two new igniters I've tried aren't correct.

????
Expert:  Pavlin Koev replied 1 year ago.
Hi, the Sensor that will make computer to retard timing is:- Knock Sensor. But the way you describing the problem is making me think that there is a problem in Woodruff key that is locking the pulley to crankshaft. if this happens, this will change gas timing. I cannot say 100% but, you can verify if #1 piston is at top position when marks are set to timing. you can use long screw driver through the spark hole feel piston movement.
4A FE does not have knock sensor though. And the fact that timing mark moves progressively is leaning towards the mechanical issue. is it possible for you to check?
Customer: replied 1 year ago.
Hi, I guess my first response to you didn't go through. The first thing I checked was TDC using a screwdriver in the no. 1 spark plug hole. Piston's right at TDC when the pulley mark is aligned with TDC on the front cover and the cam mark is lined up properly. I marked the timing belt and turned the engine over by hand to check for any missing teeth the entire length of the belt. I'm 90% sure the problem isn't mechanical, also because the car ran well (briefly) a couple of days ago well after the problem became severe.

I'm right now checking continuity in the harness, and preliminarily finding intermittent connections between the ECU and the air and coolant temp sensors. As you know, probing the tiny contacts in the ECU connector is dicey so I'm not yet ready to declare a problem there.
Customer: replied 1 year ago.
Found the problem, finally. Wrong or defective replacement distributor. When the distributor drive tang marks are aligned on the original distributor, the nib on the reluctor is about 10 degrees away from the pickup pole. On the junkyard distributor, it's about 5 degrees away. On the cheap eBay new replacement distributor, the nib lines up directly with the pole. To time the car correctly now, there isn't enough room on the distributor slot, but a die grinder and a big washer will fix that. I suspect that the reason the car began to run poorly but not consistently so with the junkyard distributor is that the speed pickup coil that I had repaired was compromised or my repair was coming apart, thus confusing the issue. I'm putting it back together now for a test drive.
Expert:  Pavlin Koev replied 1 year ago.
This is great news.

Best Wishes, Pavlin!
Customer: replied 1 year ago.
***** FINALLY FINISHED ****Put back in the original Toyota igniter, and the car runs great. Sheesh. All this time, effort, and $$$ because of incorrect or poor quality replacement parts. Thanks for you help. Wrote the following earlier today, read if your interested, don't if you're not! : Hi Pavlin, well the saga continues. I've resolved the distributor problem, which turns out to have been a totally different issue from the problem that brought the car to me this week.When I replaced the distributor a month ago with the junkyard unit, the car had a misfire on moderate to hard acceleration. That seemed to come and go, but finally got bad enough for my friend to bring back the car. I had thought that perhaps my repair of the junkyard distributor was the problem, so I put in this new, cheap, eBay distributor. Of course I chased my tail for 3 days on the timing issue, but that's now resolved. Unfortunately, the misfire on acceleration remains present. Here's what I know so far:I've checked the fuel pressure, and it's fine. It increases properly under acceleration due to the action of the fuel pressure regulator. So it isn't starving for fuel. In fact, the misfire is present even when accelerating the engine in park, where there isn't a demand for as much fuel as an acceleration on the highway.With a timing light, I can see that the spark is cutting out on cylinders 1 and 2 when the engine misses. The spark does NOT cut out on cylinders 3 and 4.The resistance of the plug wires is OK, and they are not that old. NGK wires, about two years old. The new distributor came with a new cap and rotor, and the weather is dry so I do not suspect arcing.This problem existed with the old junkyard distributor, in which I had replaced the coil and igniter. The new distributor has its own new coil and igniter, so those parts are not in common between then and now.Ideas?I do still have the used ECU I can try. Heck, I'm getting pretty good at disassembling and reassembling the console. Perhaps all these aftermarket exciters are wrong/crappy? Perhaps I'll swap back in the original Toyota igniter?I have to get this car out of here!!!
Expert:  Pavlin Koev replied 1 year ago.
Hi, thanks for the detailed information. You are correct about after market parts. They do work sometimes, but not always, and this will send you to look for the problem everywhere else and you end up spending money and time to figure out what is going on. Unfortunately the only way to really test it is to replace the part.

I am glad to hear that all is good now.

It was nice to meet you(remotely) and share thoughts

Best Regards Pavlin!

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