FuelforWar

Hey all,
Well I've been trying to fix this one for a while but its getting the best of me and i'm getting really frustrated.

Vehicle:
93 4runner
3vze 5 speed
307,xxx miles
running with 87 octane fuel.


Situation:
every 20-60 miles my truck will have a hick up. The motor will seem to cut out for a split second and bounce a lil. The problems been progressively getting worse for the last 2 months. The rate it happens seems to be the same but now the hick ups last longer. My mileage has dropped to 12 mpg when before it was consistently running at 14-16 on 35's. This week my truck stuttered at around 10mph and wouldnt take off on the freeway in stop in go traffic (always fun in the fast lane). I keep throwing parts at it trying to fix the problem from what I can dig up online but i'm having no success and I fear its going to get me stranded. I took the day off from work (after failing to make it to the freeway and having to pull off the side of the road til my motor would clear out and rev up), to address this problem. All advice is heavily appreciated.

On a side note, 2 weeks ago the odometer and tripometer stopped working, but the speedo is fine. Shouldn't be related but I thought I'd mention it.

Parts replaced and checked:

New ngk iridium plugs
Import direct plug wires
Import direct rotor and cap
New air filter
New 02 sensor
New fuel filter
Timing checked +12 degrees
idle 900 steady
vacuum lines leak free


Parts replaced last year if applicable to the situation:
Alternator
Battery
Timing Belt
Power steering Belt
Alternator Belt

If you need more info please ask .

Gevo

does it start well and idle well when cold? how does it run between cold and hot...

One thin gyou should do is isolate the problem to a system. So, is it the fuel system, ignition system, vacuum leak issue....? So you should check each system separately and confirm if it works.

I mean, it could be a million things with the information you've given so far. I would check the TPS and VAFM. With a bad TPS the car starts fine and idles fine but acceleration and deceleration seems to be affected... etc..

FuelforWar

That has been the difficult part for me. Without the problem being consistent I do not know where the problem lays. I've checked for vacuum leaks and cant find any so I can rule that out. I was thinking the filter was plugged since I've put 100k through the old one, response got better but the problem happened again worse than ever this morning. I'll look into the tps and vafm but I have very little experience with the ohm meter. I'll check what I can.

But to answer your question, It starts up right away and the idle is smooth, but it is a little rough for the first min if i tap the gas. Stuttery to say the least. A minute later thou and everything is fine and it will continue to run fine til the random problem occurs. This has happened to me at different speeds and different rpms. Not as bad at high speeds cause normally downshifting will throw my rpms high and seem to clear out what ever the problem is. However at low speeds and low rpms its a pain cause I can't accelerate up to the speed limit and the truck feels like its about to die.

FuelforWar

So I've been out here trying to re-create the stutter/surge for about 30 minutes with no luck, but something else has caught my attention I think is interesting. So I notice I cant hold the idle between 1500 and 1750 rpms. It hits the 1500 mark and shoots up to the next mark no matter how carefully or slowly I try to put it in between. When i let of the gas it kinda hits the 1750 mark and kinda has a bounce back to idle really fast. Just alil more info in case this is a sign to someone.

scope103

Actually, it kinda sounds like water in the gas. Water is heavier than gas so it can't be much (the fuel is pulled from the bottom of the tank, of course), but it might be enough to slosh into the pickup and cause a problem.

I've never tried it, but a bottle of HEET might be worth a try. It's mostly methanol, so it mixes with the water and carries it through the fuel system. For not much money, you'd at least eliminate one possibility.

How did you pick out +12° degrees timing? It's on a sticker under the hood, and mine calls for 10°. Don't forget to use the jumper when setting the timing. I'd be surprised if 2° is your problem, but one step at a time.

Gevo

Fuel in water seems interesting.. never thought of it as a problem.


You know what came to mind when you said your idle jumps.... The little vacuum valve controlled by the pressure in the steering pump can be jacked up. I know that it bumps the idle when steering fluid pressure drops for stationary steering. I don't think it's related to your main problem though...

Using a multimeter to check resistance is easy, just follow the FSM diagrams of which connectors to test against eachother, read the OHMs from the meter and compare with what it should be. I think a bad TPS and a VAFM can cause similar symptoms to what you have.

FuelforWar

That could be a possibility, not sure if this story relates but several months ago some jack ass cut the lines on the top of my fuel tank (not that hard with a 3in body lift), and I didn't notice for a couple days. My road is an awful mucky pop holed mess so water is constantly being thrown around. I wouldn't be surprised if I aquired some though the open lines..... but that was a good while ago and one would think it would have dried by then. Condensation would be a higher probablility of water collecting in the tank. Either way I just went for a test drive with my egr vacuum line unplugged to see if there was a change. After many attempts I was able to make the stutter happen again when romping it up to 60 in 3rd when it hit the 4500 rpm mark. Read your post on the go and swung into the oreillys here at yelm and looked at that heet bottle you referenced. I decieded to buy the seafoam instead thou. It said it had moisture control, along with some other cleaning capabilities so I figured it might do more good than just the heet.

Now for the timing I heard the setting should be 10 but some put it at 14-15 for better throttle response times, I picked around 12 for in between the two. I however did not use the jumper... so I'll be rechecking that.

FuelforWar

Seems simple enough, I've just never been in a position to need to use one. I'll do some research with that to make sure i'm not using a wrong setting or something. I have the fsm so i'll look into the tolerances. However thou, if it was the tps or the vafm wouldn't my problem be more consistant than just the chaotically timed engine fart that I seem to be having?

FuelforWar

Being as high mileaged as it is (specially for a 3vze), is there other odd little things I should be considering? Fuel pressure regulator, fuel injectors, sticky lifters, relays, fuel pump, ect ect ect...? Ive noticed the further from the 250K's I get, the harder its seeming to figure out the problems that keep springing up.

FuelforWar

This little engine gremlins starting to get to me. So my VAFM checked out just fine, but the TPS is extremely difficult to get to while on the truck. Out of curiosity I pulled the TPS plug to see if it would make a difference (it didn't). Afterwards (should have done this first) I decieded to see if there were any codes even thou the check engine light isn't on. Well the tps code came up. Which makes sense since I disconnected it and ran the engine. So I cleared the code and went for a drive to try to trip the code again if that was the issue. Now the dam truck is running fine and I cant get it to stutter. EVERYTIME I took it out this morning it stuttered and surged. 30 minutes worth of driving in various driving patterns I cant get it to act out again....... Resetting the computer wouldn't have cured another issue it might have been having would it?

scope103

Well, resetting the computer will force the computer to re-learn the mixture offset. Which could have "fixed" the problem.

Alas, it doesn't explain how you ended up with a mis-learned mixture in the first place.

I suppose you could have had a loose TPS connector connection, which you actually fixed.

FuelforWar

Well time will tell, its a long drive to Seattle to my house. I hope it doesn't die on the freeway again. BTW anyone who honks at someone with there flashers on is a D bag IMHO.....

FuelforWar

Dam... i just dont get it. Drove it for 35 mins yesterday and it ran fine. Then drove it for another hour and a half this morning and it ran great. Soon as I hit seattle it lost all power again and I had to pull off the freeway. It wouldnt rev up past 2000 rpms. Even when I slammed it down a few gears nothin would let me rev it up. But as always sat on the side of the free way for a min or two tapping the gas and it cleared out. Runs normal again. What can this be???????

Gamefreakgc

I have this exact same issue, where it cuts out for a split section and just keeps going. Never did fix it, just learned to live with it. Although mine never cut out completely like yours did.

What I learned is that it's eletrical, somewhere. The reason why is if you have a CEL on and it does the sputter thing, it clears the CEL. Only way it could do that is by losing power from the battery or the EFI fuse. Here's what has been replaced (for other reasons) since I first had the issue:

Distributor
Spark Plugs
Spark Plug Wires
Ignition Coil
Injectors
Timing Belt

It's not fuel related. And resetting my EFI fuse does not make it go away, in fact any time I work on my truck it happens more often, then becomes less frequent over time.

My educated guess? There's a short somewhere in my engine wire harness and every time I move it around it makes it worse for a time. I've given up on it, since it doesn't affect my rig's performance at all, it's just annoying.

Forgot to mention, I also have cleaned and re-connected every ground for the engine and ECU. Found one that was really loose once... but didn't change a thing. I really wish that I could say there's a solution to this issue but I've made threads myself before and nobody knows this one. Sorry that yours is so bad that it won't run sometimes.

FuelforWar

Hmm thats a possibility... my cel never comes on during any of the sputtering and its progressing into more than just a hick up. It lasted for a few mins this morning. I fear its gonna get to the point where its gonna stutter and not come back.... gonna try to pull codes at lunch and see if it throws a code 41. If not im at a loss for what this is...

bbrideau

My wife's runner is having the same issue. It's almost like its cutting fuel for a split second and truck will chug, if you back off the gas and give it gas again sometimes it stops the problem. Havn't checked for any codes at all. If its warm and idling it has a rough idle bounces up and down almost dies sometimes. It has me stumped so i am curious to see what you come up with, I will also let you know if i figure anything out on my end.

FuelforWar

Thats how mine seems to be running when it sputters. During idle its smooth thou. Have either of you checked your vafm or tps? I suspect it may be my tps....

bbrideau

Yea somtimes the truck drives completely normal. I do know that before all this happened it seemed to be running rich not by to much but it was running a little richer than normal. It might worth while to check out the O2 sensor/sensors? can't remember how many the 3vz has. I havn't checked the vafm or tps yet. I do have a few spare VAFM's for the 3vz might be worth swapping out for ˟˟˟˟˟˟ and giggles. will try it out later today or whenever the wife is able to leave the truck at home and let ya know

Devwon

Been fighting this for months, just got it straightened it out. Did the regular tune up stuff, pulled the codes, replaced 02 and tps as needed and still had the same issues but never threw another code. Then did the VAFM, checked throttle body,searched for vac leaks, tried all the easy and cheap stuff the fsm recommended, did nothing. I then checked and changed plugs again(#5 was suspect), replaced the coil and noticed a bit more power but it still hiccupped randomly. That led me to check the timing again which was off because I didn't know the jumper was necessary. Before you do anything check your plugs for any issues or signs of wear to rule out cylinder issues and give a clue to how your engine's running . Then set your tps to spec(it's a pita but doable and good practice for using the ohmeter) and get the timing done correctly with the jumper installed. Without that jumper in place while setting your timing it will be off. Grounds, fuel pump, coil, circuit opening sensor and ecm would be the next thing's I'd check. Good luck!

FuelforWar

Good info. I already inspected most of what you stated. Got the full tune up and a new o2 sensor. Gonna look more into the tps today and double check my timing with the jumper. How does one check the ecm?