az4x4runner

So my truck has been misfiring occasionally under load, and is slowly becoming almost always under load. I've read the numerous posts on the 3vze missing here, most of them point to the TPS. However, I tested my AFM the other day and the weird thing is when I open the plate in the AFM by hand, the resistance is supposed to climb as far as I know (to 1200 ohms or so). On mine it jumps around one spot then actually drops (from 600 ohms closed to about 400 fully open).

Sounds to me like this is my problem, as it's only when the engine is under load that is misses, which is where the resistance takes a dive on my AFM.

I am mainly just looking for some opinions as this is not a cheap part and none of the local junk yards here have one. I'd likely get a remanufactured unit from AutoZone for about $190.

If it were the TPS wouldn't the truck run pretty poor overall? It runs fine once it stops missing. Same power I've always had.

az4x4runner

Sorry for the ramblings, I had another thought...

If it were my TPS would it act up with the throttle in the same position every time? I ask this because it doesn't miss under acceleration up small hills around town, it is mostly when accelerating to freeway speed to trying to gain speed on the freeway.

az4x4runner

No ideas? Anyone here have their AFM go out? What sorta symptoms did it have?

rlordjr

I'll give this a bump. I'm interested in solution as well. I have a kind of rough, lumpy running problem sometimes that I'm tracking down that this thread may help. And no, the rough, lumpy running is not caused by me being fat or having a rock in my shoe. I'm referring to the truck.

I have replaced the TPS and that helps, but as others have noted, adjustment is a PITA. MUch easier with TB removed and sitting on kitchen table.

Lex.Luther

I have had problems with cylinders missing on both of my 3VZE's. It was two different problems: one was a bad injector (very rare but that is what it was) and the other was a valve that needed adjusted.

In both cases, the first thing I did was reach under the plenum and disconnect the injector of the suspected cylinder to validate the issue was definitely a simple case of a skipping cylinder. The first time it happened, I was myopic in my thinking that it had to be ignition, ignition, ignition. I wasted a lot of time in that regard as that wasn't the problem in either case. In the instance that it was a valve needing adjusting, I could not have been more shocked. Holy Cow! The truck went from running like abslute crap to purring like a kitten. And, I have just overhauled the top of the motor. Apparently my math on that particular valve was a bit off.

az4x4runner

Hey thanks for the reply, I am suspecting is was a dirty injector now.

I went to AutoZone and the guy let me test a working AFM to see how the reading compared to mine. It was more in the center of the acceptable ranges, but not much different from mine.

After talking for a while, we decided it may be a fuel system problem, particularly an injector. I bought a bottle of Lucas fuel treatment, been running it this last tank and have not had another miss.

Hope it was really that simple this time...

Lex.Luther

Good luck, my friend. Those injectors generally stand the test of time. The 'bad injector' experience for me was my own fault. I tried swapping out an extra injector left over from my '88 with one in the '95. They have a different connection and it stopped working after a couple of weeks. Ooops.

The injectors have very fine screens in them which can become clogged. I have always run the very best gas in these trucks (people tell me I waste my money but it's simply a habit I formed.) Perhaps that is why the screens on mine (both engines) were perfectly clear when I pulled them and checked them out. I am not an expert; however, I suppose running cheap gas could result in those screens getting clogged up. I am not hinting you buy crappy gas...only that something may has caused yours to sludge up. So, the decision that you and your parts guys came to is a pretty good one, I think.

Best of luck.

az4x4runner

Well, no misfire since running the Lucas stuff. I really hope it was as simple as it's seeming to be.

I am guilty of running the cheapest gas I could find for a while, money has been tight. I am trying to avoid the cheap stations or the ones that are being refilled at the time.

Who's gas is known the be low grade? I've heard alot of bad things about Arco, what about grocery store stations like Fry's etc.?

Lex.Luther

It's a good question and one that is not as easy to answer as it once was. A couple of years back, I read an article in WSJ stating that 'all gas' really is the same. Apparently, all of the major players pump massive amounts of gasoline into a single pipe that runs from the SouthWest (probably Texas) to the Central and NorthEast U.S. Then they offload the same amount they put in. So...the only real difference is the additives that they put in after the fact.

When I was younger, there was nothing that compared to Amoco's 'white gas.' That was their premium and it was water white. That is not the case anymore.

Nonetheless, old habits being what they are, I continue to run Amoco premium. As I said, most people would say I am an idiot. Maybe so...but here is the thing: consistency counts for something. Different gases have different characteristics, everything from how they form an aerosol to the number of BTU's produced per unit mass. My hypothesis is that it cannot help an engine to constantly throw it change-ups in this regard. An engine likely develops a rythm based upon a certain burn profile and, over the years, keeping that constant is probably a good thing.

My only advice -- and it is worth exactly what you are paying for it -- is to pick a major brand (i.e., a company that refines their own crude oil) that does not contain alcohol or MTBE additives and stick with it. You probably want to stay away from the independents as what refinery their gasoline is coming from is probably a crap shoot.

Glad to hear she's running smooth again. I'll keep my fingers crossed for you.