83 Celica GT Backfiring/bucking when warm

[Govinator]

Hey there, I'm new to the "wonderful" world of Toyotas. Most of my experience is with pre 75 American cars so I need a bit of help with it.

The car is an 83 Celica GT with a 22re and 5 speed with around 145k miles.

The issue I'm experiencing is what I think is a lean condition once the car is at operating temperature. While the car is cold/ just warming up it runs great and has plenty of power but slowly as it does warm it starts to backfire and surge.
It will first start where anything above 4500RPM it has no power and starts to buck, then as it warms it lowers the RPM range where it has no power going all the way down to 800RPM.
I have noticed if I turn the car off then back on again it will raise the range that it does have power.
I've replaced the obvious things that might cause this, (Coil, Plugs, Cap, Rotor, Fuel Pump) Timing has no effect on it. I don't think it's a bad EGR, I disconnected the vacuum lines to it and it had no effect. Unplugging the TPS does nothing.
The only things I have left to check is the ECM, Ignitor, Injectors, and Air Flow sensor. While I haven't changed the fuel filter(waiting on the part) I don't see it being the cause as the in pump cone filter was clean.

So if anyone can think of what I might have missed let me know cause this thing is driving me nuts

[twotone_ra64]

Hello and welcome to the land of Dragons! How does the O2 sensor look?

[Govinator]

Ah, forgot to add that. I have already replaced the O2. The original did have some build up on it but the new one didn't make a difference. Right now I'm cleaning the throttle body and plenum they were both coated in carbon. I also checked the AFM and it looked good other than E2 to Vs when closed read 263ohm instead of the max of 100ohm, though I don't see that effecting it.

[twotone_ra64]

I wonder now if the EFI coolant temp sensor is any good. That would definitely cause a lean condition when hot if the sensor is bad.



And if you need to replace it: https://www.toyotapartsdeal.com/oem/toyota~sensor~water~temperature~for~e~f~i~89422-30020.html

There are used and aftermarket options for that sensor, but OEM is king.

[Teranfirbt]

I would suspect a failing ignitor over the coolant temp sensor, but the sensor is easy to check. The ignitor on an 83 can be replaced with a 4 pin HEI module, since the factory style ones are hard to come by.

[twotone_ra64]

I would suspect a failing ignitor over the coolant temp sensor, but the sensor is easy to check. The ignitor on an 83 can be replaced with a 4 pin HEI module, since the factory style ones are hard to come by.

When I was writing my last reply, I was going to mention the igniter as well... but when mine was going bad, it didn't produce the same effect that Govinator is having.

In case it is bad, here is my post / wiring diagram of the HEI module swap: https://www.celica-gts.com/forums/index.php?topic=30554.msg435579#msg435579

...you should get the Standard Motor Products LX301T module.

[Govinator]

Thanks for the diagram. I checked the coolant sensor in water and it reads about 20 degrees hotter throughout. Since its a cheep part probably a good idea to just rule it out. Also the injectors all read 2.8/2.9 ohm so I'm thinking its probably not them, though I'm going go clean them anyway.

[twotone_ra64]

Cool, let us know what changes!

[Govinator]

Well still no change, I ended up replacing the injectors as well since the plastic tip on two of them crumbled when checking them so 4 rebuilt ones now. I replaced the fuel filter, the even though the origional still looked brand new inside. Replaced the EFI coolant sensor. I cleaned the plenum, egr aswell as made sure it worked properly, and the inlets into the plenum. I also cleaned the throttle body and adjusted the TPS. I did the HEI ignitor swap aswell. The only things left I can think it could be is the ECM, The AFM, or that there is still a fuel pressure problem. Is there a way to check the Computer to see if it is faulty?

[twotone_ra64]

Wow, cool you've gone through all of the motions to replace and check parts. That's what I like to see!

To check the ECM itself... not sure. I'll check the factory service manual later tonight. To start, you could bridge the check connector (yellow round plug, two pin, near fuse box/LH frame rail with grey plug), turn the key to ON, and see if any codes pop up via blinking of the CEL.

[sirdan]

Maybe the magnetic pickup in the distributor is bad?

[Govinator]

Ok, so I tested the ECM the way that the service manual lists here, and it all matches up.

I then did a visual inspection of the board and did find some corrosion and possible leakage out of the 100uf 16v resistor though I don't know it it would be causing the problem, other than that is all seems fine

I did however catch it doing something odd when I would give it like 1% throttle it would raise the RPM then drop and then raise again, here is a video of it. I'm just stumped as to what it could be, I will check the pickup on the distributor as that is one of the last electrical pieces that hasn't been checked.

here is the video https://youtu.be/h23nx7mHKlU

[sirdan]

I think the rpm surging might be a tps issue. could be adjustment. I know on my truck I changed the tps and tried adjusting it a bunch but it does the same thing but it does it at super light load like 1% throttle. Ill probably put my oem one back on as changing it didn't solve my original issue anyhow.

[twotone_ra64]

I then did a visual inspection of the board and did find some corrosion and possible leakage out of the 100uf 16v resistor though I don't know it it would be causing the problem, other than that is all seems fine

I did a similar repair to our 1992 Ford E-350 PCM, as the capacitors looked the same, and it seemed to help smooth things out. I think I have a spare '84 A/T ECU lying around that I could ship you.

[Govinator]

Perhaps it's the TPS but I think I did the adjustment right, it was correct on the bench. It's also intermittent because after that I turned it off then back on again and it wouldn't do it, if it was the TPS I would think it would always do it. Would that 84 one work? I have a manual 5 speed one. part # is 079700-0652