thook

I'd been having some major running problems with my wife's '92 4rnr. Hadn't quite ironed it all out yet, but here's some things I figured out/learned along the way. I thought I'd share, so........

First, if you suspect you have one or more cylinders not firing (which I did), you have to figure out which one/s are not working and if it's spark, fuel, or compression related.

How I did it....

A common way to tell which cyl's may not be working is to pull an ignition cable from the plug with engine running. If the cylinder's dead/not working, no change will occur in how the engine is running. However, what I learned was this method is potentially damaging to the ignition components. That voltage has to have a ground and if it can't find it through the plug/cylinder head, it will through your hand or simply feed back into the coil. Not good. So, the method I used was to cut a piece of narrow vacuum line, plug one end up to the cap end of the IG cable....starting at terminal #1 on the cap.....and stick the other end of the vac line into the distributor. I had to use a piece of a common nail cut to about 1" in length and stuck it in the vac line because the vac line itself doesn't fit into the cap terminal. The nail, however, does.

Then, with that vac line/nail bridging the cap terminal and cable, I used a jumper wire with gator clips. With vehicle running, attach one clip to the vac line at the cap and briefly touch the other end to the neg battery terminal. This grounds the spark signal that would otherwise reach the plug at the given cylinder. If the engine idle drops, that cylinder's good. If it doesn't, the cylinder's not working.

If you got a spark while testing this way, you know you're getting spark, but you gotta determine if the plug is working/giving spark......that is if that cylinder's dead. Of course, the standard procedure for pulling the plug and grounding to the head or somewhere with the IG cable intact while someone bumps the key applies here. If you get spark there, it's either compression or fuel related.

Go through this procedure on every cylinder/cap terminal. On mine, I determined cyl's #1 and #4 were dead. But, I was getting spark to every cylinder, so I ran a compression test. Came out 165-170 on every cylinder. (Follow FSM manual for compression test procedure). The compression was all good....YAY!!!.... so I had to figure fuel was not getting to cylinder properly if at all. A stethoscope can tell you if the injector's even firing off/pulsing, but if you can't reach the things because...duh........the plenum is there, you gotta pull the plenum.

Here's the laborious (yet fairly simple) part......

To test injector function with the plenum off (I'll trust you know how to remove it. If not, check out the FSM...and you don't need to pull all the vac lines off the passenger side...just the one to the PAIR valve)....

First, relieve fuel pressure at the regulator by applying vacuum to the regulator. Your facial orifice (pie hole to any knuckleheads) will work. Then, disconnect the fuel lines at the injector rails at either end. Do this at the pass side of the rails.......it's easiest...trust me! Once you have those taken loose (don't lose the crush washers down in the motor. They're not magnetic), remove the four nuts that hold the rails down to the lower manifold. Then, pull the rails off. Start at the driver's side keeping the injectors intact. If the grommets in the manifold are stuck on the pintle caps and want to come up with the injectors, just pull the grommets off and stick'em back in the manifold.

Okay....once the both rails are up with injectors attached and electricals connected, reattach the pass side rail to the fuel lines. Then, place some baby food jars (are perfect, but anything similar that will fit under the injectors will do) under each injector and allow the whole assembly to rest on the manifold.

Pull the coil wire from your distributor cap and ground it to the driver's fender or something. You don't want spark at the cylinders, eh. BUT! Keep the dist. pickup coil connected. The ECU needs that to fire the injectors.

Now, have someone bump the motor over a few times while you watch the injectors. The baby food jars without fuel, or very little compared to others, will be at the injectors not working.....obviously. If they're not working at all, you gotta determine if they're getting voltage. So, with your handy noid light (rent at O'Reilly....the one labled "GM pfi" works on the Denso) , check the connector. If it's getting volts, the injector's toast and needs servicing or replacing. Usually just servicing, but two I sent off were actually dead....kaput...pffth! So, I got a couple of reconditioned ones to replace them with.

Even if you only find one not working right, send them all off to be serviced at once. Once you get them back, <<<test them>>> using the above procedure. Make sure they work before you put everything back together. Trust me!! You'll be sorry you didn't if any are not working despite servicing. It happens.

Once you have everything all back together, take it for a test drive. You may find you have to tweak the idle and/or timing a bit. Certainly the ECU will need some adjusting, but that will take care of itself.

That's all.

scope103

Nice writeup. Systematic, step-by-step diagnosis often beats "any suggestions for what to replace next?"

Nah, don't worry about that. You replace them with new ones every time they're taken off. Didn't you?

(They're aluminum, though some folks on this forum have used copper brake line washers.)

thook

I said I hadn't ironed everything out in the original post, but.... folks....guess what? The heart of the entire problem I'd been having was the fuel pump I put in only a year and a half ago....FROM O'REILLY!! "Air Tech" brand.....China junk.

I put one in my '86 22re over two years ago and, so far, no issues. But, a couple of weeks I broke down in the '92 30 miles from home with an 1100lb trailer in tow because the pump crapped out mid hill. A big hill!! I had to drop into 4/low to get up it, cross the intersection, and make my way down a short, dead end, neighborhood road so I could be there for 10 hrs. and 'til three in the morning to change it out.....with yet the same brand of China junk. It was my only option at the time. It has a one year warranty. Before that one year is up, though, I'm yanking it and putting in a Denso from online. No one save the dealer has them.

So, yeah, Air Tech....don't get one unless it's just your only option. After reading the web, talking to folks I know, and my own experience, the brand is hit or miss. Mostly miss.

My theory is that when the 4rnr first began having starting issues when hot was that the check valve began failing causing pressure bleed off. Over time, it just got worse and the symptoms got worse up until the final dump it took here recently. I never wanted to suspect the fuel pump because I've always had good luck with O'Reilly pumps. If I'd had a way to check pressure and even thought it might be related to the pump, I'd have not found myself in the same situation. I did suspect a fuel pressure problem, but figured it was either the regulator....which was a fairly new Denso unit...or the injectors. I replaced the regulator and had the injectors serviced, though. But, now I know.....it the was the pump. Or, is it lump? (......of crap!!)

Ralphthe4runner

When this was originally posted I was just able to drive and only

Anyway I've done this experiment to troubleshoot my no start issue where the rig will sound like it wants to start up but doesn't. So i have a question regarding the amount of fuel i should be seeing coming from the injectors.

Mine looks like a dribble from all of them which doesn't seem right but i know it only takes a small amount for ignition to happen so how much fuel and what output(spray i assume) should i be seeing when they pulsate in this trial?

thanks from the year 2019

.

scope103

If the fuel system is working correctly, you will get a very fine, almost invisible, spray from the injectors. If the pressure is way too low, you'll get a dribble.

I've never tried thook's method exactly. Frankly, I would expect the fuel pressure to push the injectors out of the fuel rail. Installed, the injectors are squeezed between the rail on top against the cups in the manifold on bottom. Without something holding the bottom, only the (small) friction of the oring holds the injector into the rail.

My guess is you're not getting enough pressure from your fuel pump. A fuel pressure gauge will tell you quickly. The most common (practical) gauge has a Schraeder connector, which you don't have, but you can get a banjo-to-Schraeder adapter.

Ralphthe4runner

Took a hiatus from this project for the holidays and other family stuff

You were right @scope103 when i did my injector test the injectors blew out of the rails so i redid the experiment with the injectors barley touching the bottom of the jars and that's when i got the dribble. Even though I've done a fuel pressure test (40psi) the fact that the injectors were blown out in test 1 told me the pressure was good.

Anyway this truck had the original injectors so i decided to by new ones and change my fuel filter to rule that out and i'm still getting the same symptom= a dribble out of all 6. With everything put back together the truck will sound like its bout to fire up but because there's not enough fuel getting in the cylinder, it fires one time and shuts down. Each time i try to crank it the results lessen.

I've checked my grounds for the rails- the one that comes from the harness that goes near the rear side passenger cam and clip/wire that goes to the intake manifold.

Any ideas on what to check next?