Gravehunter

Well i put lean in the title.. but meant to say missfiring. anyway...

I have a 1990 truck with a 3.4 out of a 95 t-100 in it.
Ran good after swap for a long time.

First: i'm a 100 miles from a Dealership so i'm trying to do this myself first.

Its developed a miss/surging in it below 2500rpm.
Most noticable/bad when i'm in OD running down the road at 1500-1800 rpm. Its just enough to basically not be able to run in OD due to not enough power to maintain speed.
Its only thrown a code once while driving it down the road. That was a P0301. Otherwise it only throws codes somtimes while idling or coasting to a stop sign. Which is then either a P0301 or a P0170.

The miss is usually very mild.. but somtimes it will jerk the truck pretty hard just a second or 2.

What i've done so far:

compression check on cyl #1: 185lbs

Leak down test: 7% at 100psi

Cat is new(about 6000 miles on it)

Fuel filter is new

both O2 sensors are new(about 600 miles on them)

MAF sensor was cleaned. I also have a spare MAF and i swapped them.. but no change

Plug on that cyl is a sooty black(not wet) and will go back to sooty black even after a plug change almost immediatly.

plug wires are new

I found a questionable plug boot(on cyl#3) that looked like it was shorting out. I changed the coil pack and boot. nothing.
Moved that new coil pack to the #1 cyl.. nothing
hooked up a timing light to the spark plug wire off the #1 cyl coil pack and drove it down the road till it started missing. The light on the timing light stays constant indicating to me the spark is staying constant.

I check resistance on all 3 injectors on that side of the engine. all are within .1 volt of each other. 14.2 cold and 16.3 hot after driving a while.


Unless the injector can check ok at rest.. but then maybe going bad during the studder(where i can't check it cause im driving) it seems like the injectors on that cyl is good.

Going to see if i can test fuel pressure to the rail today. I have the stock 3.0 fuel pump in it. But it seems to rev out ok when i get over 2500 rpm. so id think if it was a fuel pump getting weak it would not run better at higher rpm.?

Any other ideas?

Gravehunter

Well i don't have any way to check fuel pressure i guess.

Seems to me it would be the #1 injector sticking open somtimes.. I wouldn't think if it was stucking shut it would make the plug sooty.
maybe flooding the cyl?
Seems odd if it was a weak pump that it would only effect the #1 cyl.

TOYOTA 1

have you tested the wiring going to that injector?

Thelast83inNJ

Too much EGR? Does it have an EGR? Is it near #1cylinder? Pull vacuum hose and try.

Gravehunter

Checked the connector and what wiring i could see by just looking at it.

How could i test it with it with a meter? Should the injector have 12 volts to it at idle or?
Its firing at idle i'm pretty sure.. i guess i could rig up my multi meter to the positive lead so i could see the voltage while i drive to see if the voltage drops or quits.

I rechecked the cylinder on the other side that that #1 coil goes to. The plug is still clean. So i feel confident its a fuel issue now.

Gravehunter

Nope no EGR on this 3.4.

I've sprayed carb cleaner all around while its running to check for vacum leaks etc... nothing.

Dvold

I had intermittant misfires on cyl's 3 and 4. Cold resistance on #3 was 14.9 and #4 was 203.XXX. All the rest were between 12.5 and 13.6. I think the book says they should be approx 13.6. I replaced #'s 3 and 4 and haven't had a problem in 4 months now.

Dvold

BTW- 97 4Runner with the 3.4

Gravehunter

thanks for the info.

Mine on that side of the motor are all within spec.. but if the #1 is going bad intermittantly it may be testing fine when just sitting there.
I'm going to see if i can rig up my multi meter today to that cyl and monitor its voltage while driving(where it hits that spot).

I also may move the injectors around and see if #1 clears up and then say #3 starts to get a sooty plug. I think that would tell me if its the injector.

Gravehunter

ok... more testing today.

I hooked the multi meter to the #1 injector and duct taped the meter to my windsheild. the injector never loses voltage while the truck is throwing its studdering/missing fit going down the road. Its a contant 13.90-14.02 volts

I pulled the fuel rail and the #1 and #3 injectors and swapped places with them. Thinking if the #1 injector really is bad it will cause the #3 plug to get sooty now since its in that cyl.
Test drove... nope. Still studders and the #3 plug is fine.

More testing...: Put in new plug.. drove stop and go traffic in town for 20 min, pulled the plug.. its clean.
Drove home 18 miles with it out of OD.. so the rpm's never dropped below 2500.. got home.. pulled plug and its clean.

Go drive.. normally on hwy in OD... pulled plug.. sooty.

TOYOTA 1

ok so,

its not the injector.

its not valves, (compression/leak down test confirmed).

no vacuum/intake leaks,(flammable spray confirmed).

its not the fuel filter, (has new one)

its not the maf.

sorry just recapping a lil.

this is interesting, usually the problem would have surfaced by now with everything you have checked.

the injector plug has two wires correct?, one hot all the time, and the ecu sends a ground to the other wire to fire the injector. did you test the ground also, or just the positive?

here is a link to some FSM's, https://www.yotatech.com/forums/f115.../#post50938942

Gravehunter

I know.. its really frustrating me to say the least. Was a bike mechanic for 12 years and i've always been able to figure out whats wrong with my junk till now.

Yah its 2 wires.
Well with the truck running i pulled the connector off the injecter and used both wires to test for voltage and it read just fine.. so the negative works there anyway.
BUT... i didn't test the negative side while driving. There wasn't any way to keep the meter leads in the connector so i stripped some rubber back on the hot side and did a quick soder to hold it there. I just grounded the other lead to the body so i didnt have to cut into both wires. So as i did the driving test.. i was only testing the hot side i guess.
If the ECU uses the ground to fire the injector... i should do the same test but using both injector wires this time.
Thanks for the thought there... i'll do this test in the morning.

Looking over the wiring schematic now.. to see how it all ties together.

Gravehunter

Well i couldn't stand it.. i had to check it out tonight.

I pulled the ECM so i could hook up the meter in the cab. I tested continuity on the injector wires all good.
Per the EWD all the + injector wires are tied into one.... so my earlier test told me nothing.. because of the + side went out.. all the injectors would go out.

Hooked it up to the negative side.. after checking continuity. 15 miles.. and nothing.. it wont do it now! Somtimes it runs good.. for a little bit.. somtimes it runs good for days. I'll let it sit for a while and do it again tonight.. and again tommorrow.

So far both the #1 injector and the #3(i just randomly picked a cyl for comparison) run about the same voltage at the different rpms i chose to check. About 1.2v in the spot it should be missing at.

Thanks Toyota 1 for posting that!

I'll post back once i get it to miss again and see what the meter says.

Gravehunter

Well I now know what its doing!!!

Drove it some more tonight. At 1700 rpm(about60mph in OD) with about 17-19 on the TPS the #1 injector.. and #3 for comparision was reading 1.2volts while driving.

It started to act up on me tonight.. so i got it back in that senario listed above and when i glanced down the voltage was climbing!!!! 1.21, 1.6, 2.2... all the way to 3.68 volts.. then BAM... back down to 1.2 and the truck ran fine again. WTF!!?? I did it again... and the same thing happened. The voltage climbs even though i don't give it more gas.

So its just flooding that cyl with gas.


Anyone have any ideas on this? I'm inclined to think its the ECM.
My test leads are right there under the dash, one in the connector on the black/red wire that powers all the injectors(+) and on the white/red negative wire that only goes to the #1 injector. My lead is pushed right in the back of the ECM plug where the wire goes into it.

That wire is in the original 3.4 engine harness and has not been sliced or messed with in any way.

Gravehunter

Well only thing i've come up with is maybe the ECM is not getting grounded good enough. Although i don't see how if that was true it would only effect the #1 injector ground from the ECM.. but i suppose stranger things have happened.
I'm going to check the grounds again.. and maybe add another one just to be sure. Otherwise i'm left to think its the ECM. I've got a source for an ecm thats the same as mine for $75 so i guess thats not to bad.

Anyone have any other things to consider/check before getting a used ecm?

mt_goat

That's interesting, subscribing to this one. I guess you have been disconnecting the battery while messing with the wiring right? I ask because that would reset the memory on the fuel trims. Its almost like a glitch in the fuel maps.

Gravehunter

Just redid the monitoring of the voltage today in the daylight.
It will drive fine one min.. with normal voltage and then the voltage just starts climbing and climbing till the that cyl fouls out and the truck shakes/studders. Its even doing it today past 2500 rpm. It might always have done it past that.. but the other cyls have enough power in them to pull that one along and you don't notice it as much.

I cleaned all the grounds.. sand papered where they mount to.. and even ran 2 extra grounds just to make sure everything is grounded well. still does it.

Seems to me with the ECM telling it to ground to fuel it.. it has to the be the ECM. ???


oh.. yah anytime i did somthing i hoped fixed it i remove the negative battery cable to reset it.
I have a scan guage II to reset codes.. so i never knew whether i really needed to be disconnecting the battery or not really. ?

Well i'm ordering that used ECM i found for $75. #'s match. Will let you konw when i get it and test it out.

Gravehunter

Thanks for the brain storms guys. Especially Toyota 1! who knows how long it would have taken me to realize i didn't really effectivily test the voltage to the injector if you hadn't said somthing.

Gravehunter

I just read where you posted in another thread that 145-175 was decent compression. My #1 was at 185 and its got 138,000 on it. Must be pretty carboned up from all that extra fuel in it!!

mt_goat

Yeah, that's the factory spec. So you are over the spec alright.