1UZ-FE Hesitation, Sputtering, Throttle Lag, and Backfire...

[Chambers]

Hi all,

I'm having some issues with my 1UZ. Recently its becoming more freaquent, happening between normal shifts, and free revs. Most of the time when I'm cruising and do a WOT jab the engine lags, then starts reving. You can clearly hear the intake "chunk" air then it starts to rev. Sometimes it will studder and shake during the WOT jab, its laggy and doesnt rev properly. During free rev its slow and sounds like a miss. I have a video here of a 5th gear WOT jab, its difficult but you can hear the popping and studdering. I have had it backfire once by giving a few WOT jabs in sucession.

Video:
[video=youtube_share;phHulV1tq8Q]http://youtu.be/phHulV1tq8Q[/video]

I just replaced the fuel pump with a Walbro and replaced the fuel filter, so I know I'm getting fuel to the rail. I replaced the coils, plug wires, and plugs about 1000 miles ago because of this issue. I havent tested fuel pressure or AFRs yet. I have also swapped the AFM with a known working one, also have swapped and tested the TPS. The only things I havent replaced are the ECU and Ignighters.

The plugs all look the same, slightly white on the ground, electrode looks clean, soot on the rim of the threads, photos below:

Cyl 1:

Cyl 2:

Cyl 3:

Cyl 4:

Cyl 5:

Cyl 6:

Cyl 7:

Cyl 8:

I did a compression test Monday night, here are the results:

 

[toyotanos]

Distributor caps and rotors ok? Sounds like carbon tracking to me?

Could also be a lean condition- have seen that quite a bit recently. Check everything that touches your fuel system/computer signals to make sure you're not running into a bad wire/signal.

 

[Chambers]

Yea, the caps and rotors are ok, I replaced them when I did the other ignition components.

I drove the car again today, did a good pull in second gear shifted to third and bam, no power when I got into third, the engine would not rev at all. I had to let off the throttle and then get bact into it. Its like the AFM or the TPS is bad, but I know they are good... I will test them again to be sure.

I'll test the connections between the ECU and the AFM/TPS too, I wont let a wiring issue keep my car from running well.

Thanks.

 

[redrocco]

Check the crank and cam VR sensors, I had more problems with the stock crank trigger than anything else on my 1UZ. I was able to convert it to hall effect when I went full stand alone and its been good ever since.

 

[Chambers]

So I have checked over everything twice. I cant find any fault in my sensors. They all appear to be in good working order, I tested the wiring between the ECU and the TPS, no issues. I still need to test the wiring between the AFM and the ECU, but I don't think I will find any issues there either.

I did some testing, first I checked the EGR valve (just in case it was at fault). It works fine and is in accordance with the factory service manual specifications.

I also sprayed brake clean around the intake manifold to see if I had any vacuum leaks, none were present, so I induced one to see how it would react. If I had a small vac leak I might not notices it right away, other than a small shift in rpms, but if it were major I would definitely know because the engine would begin to idle hunt.

I un plugged the AFM, I got a CEL and the engine would not rev. It would idle, but would "chug" when I opened the throttle up. I couldn't attempt a road test. It actually stalled when I jabbed the throttle in succession.

Next I plugged the AFM back in, then unplugged the TPS, I got no CEL and it would almost run fine. I would think I would see a code 41 and CEL for the TPS, but none were present. There was a hesitation in throttle response but it would drive. During the test drive I noticed the same hesitation I have been experiencing was still evident.

Throughout all this testing I would feel the engine sputter and pop, then start to clear up and pull with no pops or sputters up to redline. So I hooked up my test tach. with all the sensor plugged in the engine idles at 450 rpms, all the lights are dim and when I give it gas they get brighter. I went on a test drive to see what rpms the engine "clears up". In the video below you can see its sputters until about 2300-2500 rpms then starts smoothing out, and pulls up to redline ~5800 rpms, the entire time I'm at WOT. It felt like it was really lacking in power. I also want to add, after the pull I was trying to induce the issue by jabbing the throttle, out of no where I get a CEL. It stays on for about 5 seconds then turns off. It did this three times. After I got back I checked the codes:

24 - IAT Sensor Signal (makes sense, I had the AFM unplugged)
31 - Air Flow Meter Signal (makes sense, I had the AFM unplugged)
42 - VSS Signal (I do not have the rear speed sensor like the auto boxes do)
71 - EGR System Malfunction (makes sense, I had the EGR unplugged)

[video=youtube_share;IqapedVAH5A]http://youtu.be/IqapedVAH5A[/video]

 

[Chambers]

I found a spare ECU I had, it has the same part number. When I looked up the number it appears its for a 95 SC400. Upon installing it and going for a test drive I noticed it ran EXACTLY the same... I thought my engine harness was from a 96, so maybe thats the issue. Now I just have to source a 96 ECU.

So with more research it seems the 96 harness has a different AFM and plug on the AFM. I do indeed have a 95 harness and AFM.

 

[Chambers]

Ok, So after extensive testing at the ECU using the EWD book, checking voltages for all the sensor imputs, checking for grounds, and checking for shorts the only thing I had left to check/ swap out was the igniters. So I found a set in the local pick n pull, swapped them, and it still ran the same.

But for some reason, I got a thought... What if the traction control system (sub TPS/TC actuator) was sending false signals to the ECU and it was cutting fuel/ somehow modulating the TC throttle plate (I dont think this is possible with no trac ECU). So I un plugged both, and BAM! The hesitation under ~2300 rpms was gone, the "mash cut" (as it has been dubbed by my friends and I) seems to be gone too. I have driven it a few miles since I unplugged the two components and it seems like its almost %100. I have never felt this engine at %100 so its hard for me to know, but I do feel a difference while driving it.