83 Celica GT Backfiring/bucking when warm

[twotone_ra64]

'83 and '84 both used the same EFI system with a vacuum advance distributor, so I believe they should work. '85 got the electronic advance distributor and a knock sensor, which is not backwards compatible. Could you send a photo of the connector socket on the ECU just to be sure it will at least be physically compatible? There should be a single-piece receptacle for two plugs. '85 ECUs would have a receptacle for three plugs, for reference.

The A/T variant should also work fine; when my car had the 22R-E, it was A/T, but after a 5-speed swap, I changed it for an M/T variant ECU and it was compatible.

By the way, I'm not sure that's the correct part number. Usually a Toyota part number is formatted like so: 89561-14172. Five digits before and after the hyphen.

[Govinator]

Ah ok, put the ID number instead of the part. It's a 89561-14170. The connector style is two green plugs one larger than the other. I'm going to a guy near me that has a bunch of celicas and supras he's parting out to get a new hatch so if he doesn't have one ill hit you up for it.  Also going to replace that capacitor to see if it makes a change.

[twotone_ra64]

Sounds good, the connector style is the same as mine then. I'll double check what the part # is on my A/T ECU. If you're keen, you could probably repair the ECU and resolder the capacitors yourself, since they're simple through-hole components. I think you should be able to find the 16V, 100uF cap within this kit. I got the Ford PCM capacitor repair kit from these guys as well.

https://www.ebay.com/itm/182178114381

Edit: shoot, I should buy one of these in case my 1992 LS400 ECU goes kaput...

[Govinator]

Well did some more things, put a new distributor in and it runs slightly better, takes it longer to start loosing power and the back firing is definitely better.
Cut the cat off to see if it had a restriction and that wasn’t it.
Checked the fuel pressure and it is 27 psi when idling and goes up to 35psi when reving it, so I’m fairly certain it’s not a fuel related issue.
The only thing left that I can think of it being a computer output issue it is still doing that idle surging thing. Also had a really weird issue that ended going away was when the lights came on it would almost die, wasn’t the battery swapped it with a known good one and it was the same, didn’t stop doing it until I pulled the stop fuse.
So gonna just order a rebuilt computer just to know for an absolute that it’s not it.

[sirdan]

I don't think I like that fuel pressure. I feel like it should be in the 40s. And I feel like if anything idle should be higher unless there is some kind of voltage/charging issue. Also how/where are you measuring the fuel pressure? When I did mine I had to get this adapter and gauge setup to go to the fuel rail via the cold start injector. I think other people tap into the cold start with universal gauges.

[Teranfirbt]

That's perfectly fine on fuel pressure, Toyota set it at 38psi at WOT, 27 at idle is right. I bet that cap will help a bunch, caps do weird things when they go bad.

[Govinator]

I used the loaner kit from autozone and tapped into the cold start injector.

[Govinator]

Well new computer made no difference, but I still stink it’s electrical. It’s always had all the lights except headlights when the brake pedal is pushed and now it’s doing this. https://youtu.be/cHKBRLzFUrg

[Govinator]

Ok, I looked at the wiring diagrams and there might be an issue from the cruise control computer to the efi computer where it connects through G-R.

[ozzie]

Seems like you're getting some weird backfeeding somewhere. Disconnect the taillight harnesses and see what happens. If that makes a difference, check if the 2-element brake/tail light bulbs are shorting across the two pins.

[Govinator]

Finally got around to doing a compression test, and it’s perfect while cold 165 on #1 and 162 on the rest so mechanically the engine is fine. I do want to do another check with it hot. Also disconnected the harness at the tail lights and no change so I’m going to have to go under the dash.

[Govinator]

Fixed the taillight issue, had to clean the connector for the twilight harness and replace the bulbs. The ones the guy had in it were just single filament so I put in the correct type and now it has no effect on the engine.

Did another compression test with it hot and it’s even better than cold, 170-175 on all cylinders. I’m also thinking that the backfiring is not connected to the power loss and not from running rich or lean, I checked the plugs and they are the prefect color. Is it possible for a cat/muffler to cause the sound?

I’ve noticed a change in the power loss, once it starts I can turn the car off then imidiately back on and it fixes itself for around 5 min then comes back. Is there anything that the engine or computer would turn off/on after a warm start?

[Govinator]

I’m done it’s going to the scrap heap

[twotone_ra64]

You're not serious, right? Electrical gremlins are certainly annoying but it would suck to see a whole car go to the yard because of this. I sadly don't have too many other suggestions for what you could look for, since you covered many bases, so hopefully someone can chime in. Are there any parasitic grounds occuring? The fact that it goes away briefly when the car is turned off/on is strange. Clogged cat would see high engine temps and reduced power.