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1994 4 runner 3.4L Auto, Rune rough at idle. Ign pattern looks good, compresion 150-170 all cyl, fuel pressure 40 p.s.i, timing at belt checked ok, ohmed injectors, fuel pressure drop on injectors all between 15-20 p.s.i, checked exhaust back pressure ok, noid at all inj, steady vacuum........?????? Found distributor cap was corroded and thougth a crossfiring cap wouldnt show on lab scope but after replacement it did not change. Customer rewired harness for injectors and replaced all 6 injectors. Im gettign pulse so wiring should be ok. Tried pulling wire off each cylinder at a time and I cannot find one cylinder that is worse then another im kinda lost at this point banging my head on desk. Toss some ideas if you have them.

i'de check egr valve. it may not have one. if it does, that sounds like your culprit. just in case this is one of those "duhhhh,i never thought of that". i've seen people pump dsl fuel into their tanks and have it run like this. take a whiff. if it even has what you think is a hint of dsl drain the tank. oh ya, i'm in that catagory of not looking at the fuel.

Check the fuel trims. Rich, lean?

Egr is ok sorry. Fuel smells good. Im gonna do a running compression test when I get caught up(bent valve?). Only runs bad at idle down road good but lacks power.

woahhhhhhhh here. the customer has been doing sensitive repair work here. look at the knock sensor as well as the air flow sensor.

I ran into a similar probelm a few months back. Real rough idle, & a hard restart. Turned out the the cold start injector (mounted 180' from throttle body) was leaking at all times. It never threw a code, but was way too rich causing an unstable idle. I posted a tip on Ondemand5.com regarding this issue. Maybe this will help. Good luck.

Jeremy G.

Timing is good as are fuel trims. yes they re-wired one half of the injector harness due to rodent damage. Wiring looks good and am getting noid at both sides of wiring. I wish I could narrow down the cylinder that is missfiring but So far I haven't. Im gonna do running compression later today. Vehicle starts good and runs smooth off idle just rough at idle and lacks power. I needed a break from it

I unplugged cold start injector with no change how else is this tested? What I mean by fuel trims are ok is pattern for o2 looks good. 94 pre obd2

Running compression 80-90 all cylinders.

what do you mean "on both sides of the wiring" ?

At the injectors(plug) and at the other end of the wiring so both ends

I'm wondering if the injectors are correct for the vehicle? Did the problem start after the customer did the work?

something made me think that both sides of the injector plug were firing. that would be a trick.

I wish I could find it or that is was new enough to get more comp data. I havent had one I couldnt fix in a long time I hope he gives me enough time

#2 cylinder is problem if I pull plug wire on all others I get a 100 rpm drop but not on this cyl. plug is good, inj is good, compression is good?????? dang

if i were to guess i'de lean towards a vac leak or worn cam.

Wild stuff ill try some more this afternoon

You can close this one I believe I narrowed it down to injector spray pattern I cannot verify what it looks like but it is flowing but I think it is a steady stream instead of a mist

that's great brian. just a couple of things though. if i were in your shoes with the fact that the customer had already replaced injectors and repaired wiring i would open the harness and recheck the splices. it's a multi strand and there may be an issue where you'll get voltage signal but not enough amp to trigger the injector correctly. i've seen splices where when the insulation was stripped wire strands went with it. i'm hoping butt splices weren't used. they will in some instances cause a higher resistance causing a problem. on applications like this i'll remove about an inch of insulation from both ends slide a shrink tube over one wire twist the strands together, solder it and then heat shrink the splice. i always solder but i'm old school. i'm sure that twisting and sealing the splice would be sufficient. on fine wire i'll heat the insulation to help strip it.

The wiring was good. same reading in and out to each injector. Before I did alot of testing I noticed the plug on that cyl #2 was a little wet. I replaced the plug and I pulsed the injector manually and if would flood the cylinder. I told the guy to swap the inj with another cyl and if the mis moved he knew his problem I was tired of taking that plenum off. That was my last hope since everything else tested good. I went over everything twice and even took off the valve cover to check the cam and valve clearance. Im pretty sure it is the inj at this point just wish I woulda considered its spray pattern sooner so I would of swapped it on my own. Thanks for all the help guys.