2.7L Misfire in Cylinder #4

still waiting on the LCE gauge... will update when I get it

 

OK well thanks DM93 for pointing me in the right direction. I installed the LCE gauge today and pressure on the SUPPLY side is great - 45 PSI while running and it held pressure and only trickled down to 20 PSI in 5 mins after shutting off. So I guess I'm back to square one and its not the fuel pump after all...

Really stumped at this point.

Recap:

Original code misfire in multiple cylinders after limping home
now always only misfire #4
compression test is good on all cylinders
swapped coil packs around - no change (distributorless)
swapped spark plugs around - no change
swapped injector #4 and #2 started getting misfire in both #2 and #4??
replaced all injectors (denso) and fuel filter (oem) - runs a little better, but still really rough. takes longer to throw a code, but still only misfire #4
also seeing code P0171 System too Lean (Fuel trim) twice now

Maybe I need to look at the wiring harness for cylinder #4?

Appreciate any ideas...

 

Have you checked for spark at the #4 coil and for injector pulse at the #4 injector?

 

No, I haven't. Not sure how. Can you point me in the right direction?

thanks

 

You can pull the coil out and use a spark tester or in a pinch an incandescent test light can be used if your careful and not afraid of getting shocked.
Injector pulse can be checked with a noid light or test light, one wire should have power with the key on the other will be a pulsed ground so test light connected from battery positive to that wire should blink with the engine cranking or running.

 

good info, thanks. I will do these tests and report back.

 

Update: spark test was good, Noid test was NOT good.

Got no light at all on the Noid when plugged into the wire harness for injector #4. For comparison I tested on injector #1 harness. It appears the light is polarized since it only worked in 1 orientation, but def got a bright pulse when cranking. Of course the engine starts and then immediately shuts down so only see a few pulses. However, with same orientation on injector #4 no pulses at all.

I found a good thread with wiring diagram and how to check for continuity to ECM, open ground, etc
https://www.tacomaworld.com/threads/2-7l-injector-electrical-issue.517100/

will be following that procedure next. Looks like that guy ended up having a bad ECU! eek. I found another thread where he seemed to indicate that was the solution.

Let me know if anyone has any other troubleshooting tips.

Any recommendation on where to get ECU if I need one?

Tks

 

Another update

Used a logic probe on the injector harness pins
Pin #2 shows ground on all 4 injectors with key off, and hot with key on
Pin #1 (the ground pulse) shows nothing on injectors 1-3 with key off or on, but I am getting a steady weak ground on injector 4!

I think we are on to something.. could be a short or a problem with the ECU

Diagram below shows Pin #1 goes direct to ECU, which normally pulses the ground. The wire for injector 4 is Red/Light blue.
I unplugged the connector from the ECU and tested continuity successfully. (OK I'm definitely on the right wire)

However as soon as I unplugged the ECU, the weak ground measured at the injector #4 harness pin #1 goes away. So to me that looks like the ground is not coming from a short, but from the ECU. Unless it was coming from a short of one of the other 12 or so wires that I also unplugged from the same ECU connector. So I checked for continuity from the Red/Light Blue wire to any of the other 12 disconnected wires (to check for short), and none had continuity.

So to me looks like the issue is with the ECU circuit. Its providing constant ground instead of pulsing it to Injector 4.

Thanks so much for all the helpful info guys. Let me know if you think I'm on the right track. In the meantime I will be hunting for an ECU...

 

There are ecu repair companies out there too. Could be something simple with the output circuitry like a bad transistor or failed capacitor

 

Sounds like you are on the right track.
You have several options on ECMs, have it repaired, get a reman (not reccomended), or used.
If you have an automatic transmission used ECMs tend to be pretty available and relatively inexpensive, if you have a manual though you only option may be have it repaired or getting a reman unit.

You will need the service number off the old ECM to get the correct one.
Hollander Parts is a good resource for used parts.

1st gen ECMs should be plug and play, no programming required.

 

OK interesting. Got a quote from this place, they claim to have the same part number
They claim programming is required, but they probably say that for all parts just in case.
https://www.fs1inc.com/89661-04860-...ne-computer-pcm-ecu-programmed-plug-play.html

part # on my ECU is 89661-04860, and it is a manual trans

I'm gonna open it up and look at the board for any obvious scorch marks, etcs. Might get a quote from this place on a repair http://siaelec.com/faq/
I'll try Hollander parts as well.

Thanks

 

I've heard mixed opinoins of FS1, some people claim they got good ones from them and others have said it took several tries to get a good one although in my experience it seems to be that way with all reman modules no matter the supplier.

 

Update: looks like my ECU part number is pretty rare. 4x4 with MT and SR5. Finally found one yard that had the right one. So I ordered it..

Should be here this week and I'll update.

BTW I opened up the ECU and looked at the board. Nothing obviously wrong. I found what I think is the driver chip for the #4 injector chip. It has 3 pins. I did some continuity tests from each pin to the ground pin, got the same results on all 4 driver chips though. I wonder if I would have to apply power to the board to get an accurate test. But I'm a little hesitant to do that. Well the replacement is on the way... we'll see what happens.

Thanks again

 

Update!

I got the junkyard ECU and slapped it in and it fixed the misfire!

Thanks all for the help along the way. I definitely learned some good troubleshooting techniques.

Hope this helps someone else..

 

I would check your wiring, just to be sure you don’t have some bare wires somewhere. The burnt up ecu could be a symptom instead of a a cause

 

yeah, good point.
I'll look again, but before I started focusing on the ECU I was looking for any abrasions, problems on the harness. Everything looked good and in tact, I was afraid to start unwrapping stuff and make more problems for myself...
I'll double check though. thanks

 

I learn by just reading this post

 

I tried an FS1 swap before but the key provided didnt work. The pins 4 and 13 for 30 min didnt do squat. 200 bucks down drain.