92 3vze pickup misfiring on 1 and 3
 

This has really got me stumped. Truck is a 1992 v6 4x4 manual trans 186k miles. A few weeks ago i start noticing i can feel one or two cylinders dropping at highway speed. I ordered a set of the flamethrower injectors, new plugs (denso), ngk blue wire set, and a tps. (My tps has been dead since before i owned the truck) pulled upper intake off and swapped in the injectors, installed a new gasket, fixed a couple of coolant leaks, replaced some sketchy vac lines (one at a time), put in new plugs and wires, tps set to fsm spec, (no code for tps finally!) Basically just a good tune up at 186k miles. Put everything back together and fire it up, dead on 1 and 3.
Crap, i start troubleshooting. Pull the intake back off, noid light the injector pigtails, (all flashing) swap around injectors, replace gasket again, look for vac leaks..... still no go. Pull the wire off the distributor on 1 and 3 and see spark, but no change in idle. Check timing, compression test (172-180psi across all 6) pulled plugs and im not seeing any wetness or gas smell on the problem cylinders. In fact, they smell like combustion is happening. I'm pulling my hair out, this old girl is my daily. Prior to 2 dead cylinders i did clean the vafm. Could i have messed it up? Could it even cause misfires? Coil and ignitor look original, battery is fairly old, and it doesn't even look like the alternator has ever been replaced. I bought it with a fresh reman short block 15k miles ago. Don't know any history besides that. She's been running good up until 2 weeks ago, now she's parked. Any help guys... any. Point me in a direction. Planning on going over engine with propane tomorrow to check for vac leaks, and stare at it and hope the problem stands out.....

Air leaks from the air filter housing to the throttle body can cause missing and rough idling. I had missing and rough idle on my 3.0 a few months back, replaced a cracked intake tube and it is running great.

Side note, truck has been missing a little going up hills at low speed for a while. I live in the mountains, so everything is going up hills. Truck does not like to run when parked at operating temp and tried to start again after sitting 15 or 20 minutes. Not sure if that's related, but I'm trying to paint the best picture.

My truck has the k&n intake on it, but I've got over all the piping pretty well. No cracks or holes i can see.

maybe you have already checked, but did you swap your plug wires at the distributor by accident?

I've checked numerous times, cap and wires are marked. Cap and rotor look good too, about 10k miles old.

If you have two dead cylinders but the others seem to be running okay, then it must be something to do with THOSE cylinders. You've checked compression. You checked for spark at the distributor, but a better (and easier) test is to put the inductive pickup of your timing light on each plug wire. If the light flashes, the plug is firing. Did you swap the injectors around?

If you have compression and spark, then it has to be fuel. If moving the injectors doesn't make the problem move, the most likely explanation is high resistance in the injector wiring (not so high that it won't flash a noid light, but too high to get the injector to open). SInce all 6 injectors on the 3VZE open at the same time, you could try just putting in a jumper wire from a known-working injector to your suspects. (Remember that the injector is opened when the ECU grounds the W-R wire. The B-R wire is always battery voltage with key-on.)

(Or ... could you have a blockage in the intake runner, so that those cylinder are not getting air?)

I am getting flashes on a timing light for both cylinders, and i have moved injectors around. That's a good idea, when the problem got worse after installing the injectors the first time i thought i had broken the old injector wiring when i had it apart, that's why i tested with noid light. I'll give that a shot, I'm fairly fast at pulling the intake mani now. Does the ecm ground all 6 at the same time or each bank at the same time? Schematics i pulled looked like each bank has its own pin at the ecm. But regardless, i could try jumping 1 and 3 from 5 and see if that clears it up. Im thinking it's a fuel issue as well, just because the plugs aren't wet with gas when i pull them out. After new plugs ive only run it 10 mins maybe and the ceramic around the electrode has brown "burns".

I'll check for b+ at injectors while I'm at it this morning. I removed all the old electrical tape on the harness from the main bundle out to the cold start injector to check for damages and didn't see anything noticeable.

Wiring looks and checks good. .5 ohm from ecm to injectors. Fuel rail clogged? 2 bad new injectors? One thing i thought was weird, checking resistance from the main b+ (black w/red) to the injector connector i get .05 ohm on b+, and like 5ohm on neg.... but they were all like that and 4 are working. Could bad o-rings on injector cups cause a lean enough condition to not get flame? I checked and cleaned them when i moved the injectors around the second time. None of them looked cracked or pinched, but im stuck. Is there a way to check if injectors are spraying with upper intake off?

I used this setup https://www.yotatech.com/forums/f116.../#post52330847 to look for a leaking injector. You could do the same, once you've pressurized the rail just apply 12v to each suspect injector to see if they open. (Remember that the design duty-cycle is only a few percent. Don't apply 12v for more than one second at a time. Probably much less will tell you what you need to know.)

Thank you, I'll give it a shot. At least i can make sure they all spray.

So i put strips of paper down the runners, primed the rails and touched the ecm side to ground. Heard them spray and checked each one, all have gas on them. Im putting it back together right now and hoping they'll still work. I switched bank one injectors with bank two, put new o- rings on the cups, and re- wired the ground for all 6... fingers crossed.
I also broke the bvsv... I'll just cap the throttle body for now. Not getting my hopes up, I'll probably be removing the intake again.

Before you button it up, you might try cranking it. This will directly test if the ECM open command is reaching all the injectors.

I tested that with a noid light. So maybe i got mixed up the first time i moved injectors. But the misfire followed the injectors this time. Now 2 and 6 are dead. I've contacted the company and they're sending a new set, no questions asked. Maybe the spray i got on the paper just isn't enough for proper combustion. Looks like im tearing it apart again. Went with reman injectors to save cash, and ive been without my truck for 2 weeks.