Maybe you all can help me diagnose this problem...

Hey. Well, I'll try to keep the history short because it's pretty long. Anyway, I've been trying to deal with this problem for over a month, and have done extensive research as well as tried to get help locally and on several national and international car-specific forums, but haven't figured it out.

So, the car is an 1985 Toyota Corolla SR-5 with an engine swap. The engine is a "jdm" 'blacktop' 4age (bolt in) 20v motor with "VVT". The stock motor was carburreted and the new one, fuel injected, plus there was a 10 year difference so quite a bit of wiring was involved.

Here's the problem: When it is given more than a little throttle, the engine bogs down and the RPM will either freeze up or drop, or sort of pulsate between 1500-2000, sometimes backfiring, even with the throttle all the way open. The car can be redlined, but only when the throttle is applied slowly.

So, I've tried just about everything to fix it. The ECU throws no codes, although I know the diagnosis system works because if I unplug any sensor that sensors code comes up.

The timing belt is perfect, the timing is perfect, I've checked and adjusted and readjusted the TPS numerous times (and tried it at other, not suggested positions), checked multiple MAP sensors, checked and rechecked the injectors, new plugs/wires cap/rotor, checked cam gear positions relative to cams, checked ALL of the ECU voltages and resistances listed in the FSM, 4 of which were slightly off.

The voltages were for ignition sw on, and 2 were off:

PIM-E2 (that's MAP sensor signal wire to sensor ground): 4.68V, should be 3.3-3.9V

IGF-E1 w. ignited disconnected (that's from the igniter to ground): 4.09V, should be 4.5-5.5V

Two resistances were also off. These are taken with ignition sw off and all 3 ECU plugs unplugged. These are the resistances through the wires, not on the actual ecu.

VTA-E2 throttle fully open (this is TPS signal wire to sensor ground): 2210 Ohms, Should be 2400-11200 Ohms

VC-E2 (this is +5V sensor power to sensor ground): 2060 Ohms (Should be 3100-7200) !VC-E2 voltage is spot on though at 5.01V (4.5-5.5V)

E2 sensor ground is grounded through the ECU. I've tried grounding it additionally to the engine and chassis but it doesn't make a difference (as it shouldn't).

The ECU also has a problem sometimes internally with leaky capacitors and blowing the VVT transistor. I've opened mine up and it doesn't seem to have those problems.

One interesting thing to note is that, when the TPS is unplugged, it has a little hiccup when throttle is applied, but doesn't bog down or have a problem revving up at all, which leads me to believe it isn't fuel-system related (although I do have an adjustable fuel pressure regulator on the way). Also, I have a light hooked up to show when VVT engages, and the problem always happens at the same time VVT engages. However, when the engine is below 50*C, VVT does not activate and the problem still occurs. Also, VVT will not activate when the TPS is unplugged because it uses RPM/TPS position to decide when to go.

Lastly, I sought out someone locally (relative, 50 miles) that had done the same swap that I could have test my ECU. Well, when I got there, I found out that he had the same problem as me, and he has 2 ECUs, so that's probably not it. (Although, I didn't get a chance to see if all his other stuff was done right, so I might still have to try one of his ECUs..)

So... I've just been wasting hours every day for the last month on this stupid crap that should have taken a day to figure out and don't know what to do. Any help would of course be greatly appreciated!

Over on the Toyota truck boards fairly regularly it comes up, someone with a 22RE engine that bucks and surges and won't rev up. No codes, just bizzare running. And the old fix consistently has been to make sure the coolant level is correct, and that the temp sensor is working correctly. For whatever inexplicable reason, the ECU seems to flip out if it can't get correct coolant readings.

Not saying this is your problem, but as it's a Toyota, I'd think it worth a check.

Thanks for the quick reply. Well, I checked the ECU sensor water temp voltages cold and hot and they passed, so I'm pretty sure it isn't that. The cooling system is completely custom but it shouldn't have a way of knowing how much coolant is in there. Anyhow, that's good too.

When in doubt, check your grounds (remove them all add dielectric grease and cross ground all of the if in different locations)

Also make sure your fuel pump is well grounded and making proper pressure and generates proper volume.

What igniter are you using? What fuel pump?

I'm very confident in the grounds. I'll throw some more on there and see if it does anything, but the problem seems to be more isolated than that.

Hey Hess. Stock BT igniter, '86 GT-S fuel pump.

Try a different igniter. I had a very similar experience with my ST in the MR2. Give it a little throttle and it would rev. Step on it and it would just fall on it's face, backfiring. Very difficult to diagnose with it in the driveway. It was my 4AG 16v igniter. I was a pioneer in this swap, so the knowedge base was non-existant at the time. Today, I would use an igniter from a 3SGTE or some truck (forget which one) and that would fix it. I fixed it by going to a MSD6A triggered by my original igniter.

I think there are some 2.0 celicas in the junkyard... I'll see if I can grab an igniter. How would that explain how it doesn't have a problem revving with the TPS unplugged though?

Dunno there. That could be different. On the igniter, if the plug is the same, you are probably OK. I don't know if the 2.0 celi's will work or not. With the TPS unplugged, your ECU will be in emergency limp home mode. Does sound like a sensor either bad or the ECU is reading the wrong value from it because of wiring. What MAP sensor? Was this a half cut or pieced together?

Ah I'm not actually too familiar with the Toyota engine family, I thought the Celica 2.0s were 3SGTEs.

I've got the stock MAP sensor, but I've also tried 2 from the junkyard. I forget what they came out of, but one looks exactly the same, and the other is bigger but uses the same plug. The one that looks the same, acted the same. The bigger one seemed to be a little different, but the problem was still there for all 3.

I got the harness with the engine and the car as a project someone else didn't finish (or start, even). So, I took the cut 20v harness, and mated it to the stock SR-5 harnesses and added some electronics (EFI main relay, circuit open relay) from an AW11 in the junkyard.

I'm not sure if the ECU goes into complete limp home mode.. because it doesn't have an early rev-cut or anything.

3SGTE was in the MR2 Turbo and Celica Alltrac. There is a more common motor in a Truck, Tacoma, I think, that had the same igniter, but I forget. It should be on club4ag.com somewhere and I probably posted the exact model there at one point.

It sounds to me like your wiring may not be correct. You may have a sensor hooked up wrong. Doing a cut harness is a real biatch, I know. Also make sure your fuel pressure is good. What are you using for a return line to the tank? Do you have a blacktop wiring diagram? I've only seen silvertop diagrams floating around.

Oh... yeah, none of those in the junkyard.

Well, most of the sensors were hooked up to the ECU plug already and didn't get touched. I didn't have a blacktop wiring diagram... I just used the info that's available online... (ecu pinouts, padandwheels.com, club4ag sticky, etc..)

Stock SR-5 fuel lines, although I've heard people recommend not to do that for the main line. I've tested fuel pressure and it seemed to be good ~30 PSI but the gauge was jumping around a lot, pulsating +/- 5 PSI. Also though, I couldn't get it to stop leaking, although it wasn't leaking much.

Key on engine off fuel pressure should be in the 40-50psi range minimum IIRC.

The fuel leak could be causing part of the problem but I would bet you will need a real FI pump and a better (not leaking) fuel system.

Lemme think: Fuel pressure should be 46 PSI, shouldn't it? That could be part of the problem. Check it with the motor off and the pump jumpered on. Then you can check it running, but that will move around depending on vacuum conditions.

If the harness was cut, the sensors wouldn't be going to the ECU. Someone must have wired them to the ECU. Seeing as how they abandonded the project, chances are pretty good that they screwed it up somewhere. Check every single line. That's the biatch of a 20v swap, especially with a cut harness.

A guy I know in Florida put a BT in a S2 Europa. I saw the car in Dallas at Log 26. Real clean swap. He never could get it to run right. It was fast, but not much faster than the stock motor. One mechanic he took it to said he needed a whole new wiring harness, which the mechanic would be glad to do for two or three large. I told him to find a JDM expert that knew what a 20v was, which he eventually did. Fuel pressure was low. Cost him like $50.

The actual fuel system isn't leaking, but the fuel pressure gauge fittings were (it wasn't a permanent install).

The harness wasn't cut at the ECU plugs, it was cut at the alternator, fusebox, and connections to interior harness.

Hopefully when I get this FPR things will start looking up. To me it still doesn't make sense that it could be fuel system related when it acts like it does without the TPS... unless it just has real low fuel requirements like that.. or something.

Of course, eBay failed me again. I used to have the best luck with that place, but of the last 3 things I've bought, one they sent a week late, one was a stolen phone (which I will be able to get a refund for atleast) and the people I purchased the FPR from waited for me to email them to tell me they're out of stock (even though they still have FIVE listed) and offer to send me a cheaper brand for the same price.

I checked another ECU today. No go. Same deal.

Okay... walk of shame... sorta.

Well, I was over at my buddy Ura86's place hooking up a CEL for his swap, and when I was trying to verify that the "W" wire was in fact for the CEL, I was having trouble because the wire "STA" was cut, and I thought that was supposed to be plugged in. Anyway, I got home that night and when I was going to bed, I was thinking about that pinout. I used to have it wired up in my car, but there was a bad connection and my roommate said it wasn't needed (Mr. My Family Used to Make Wiring Harness for Heart Monitoring Systems in our Basement) and that it would be cleaner to run it on the other side of the car without going to the ECU.

Well, it started fine that way and I didn't realize anything had changed because the TPS plug at the time wasn't grounded well. (I had used a pin from another plug that wasn't the right pin.. but it was all I had.) I got some new TPS plugs from the junkyard and when I replaced it, it ran like it was running. I figured the problem was always there but the TPS was never grounded. Well, it may have been, but probably wasn't.

So, when I woke up today I thought 'what the hell', try jumping the starter trigger wire to the STA. So I do it, and I'm afraid to give it gas because I don't want to have the dreaded bogdown again. If I try something new and it happens again, I'll probably have to kill myself. And it isn't there! Wait... try again. It's gone!!! Are all the sensors plugged in? Yes! VVT is working! Holy crap!

So I unplug the wire I had jumped... and the problem is still gone!!! WTF?! That means I didn't do anything and it fixed itself?? Try it again without the wire. Problem is still gone. OMG I swear I'm gonna kill this car. Well, I figure the ECU is a bitch, maybe it likes to store weird stuff in its memory. So I cut the power for 5 minutes. Turn it back on (without the wire), and the problem is there. Thank god (as long as it goes away again). I plug that jumper wire back in and its gone.

So kiddies, yes, that STA wire is important.

Well ya'all coulda probably told me that... but I thought it was important in the first place. It was just bullE36 M3 how the problem got masked by the TPS sensor for me...

I'd like to thank everyone for their time and suggestions :]

damnit, i was about to recommend you try a shotgun.

What's the STA wire? I don't have a wiring diagram but I'm planning on putting a blacktop in my AE92 if I can ever afford one.

Starter.