86STLRunner

Hey guys,
I've spent a couple weeks trying to diagnose the problem in my 86 runner. Here is what's going on and how I've gotten it to change.

The truck idles and runs perfectly. If it sits for a period of time, it seems to run ok. It responds better with very light throttle. If I get into the throttle too much, it will start bucking and falling on its face. It does not feel like a misfire. More a complete power loss. It doesn't hiccup at all unless it's a total power cut. It seems that if I shut off the car while driving, and then pop start it again, it will gain some of the power back. But the issue comes back, sometimes in a few miles, sometimes instantly.

First was to check ignition.

Plugs are new and look perfect
Wires are new and look fine, none are melted or anything wierd.
Cap and rotor are newer, I sanded the contacts to make sure
I swapped the coil/igniter with a buddies that runs perfect. No change
I swapped the dizzy pickup with the same truck, no change.
Timing is good and is slightly advanced.
Head gasket replaced within the last 300 miles.
Good high compression.
Swapped coil wire with known good one, no change.
No codes shown, when I do the paper clip jumper, it idles down and flashes the CE light every 4.5 sec.
The tps is new and ohmed to spec. I even pulled it off and rechecked it again. It's within spec.
I swapped the AFM with the other truck, no difference.
I swapped the o2 sensor with other truck, no difference.
Checked all vacuum lines, hoses etc. Compared them to the good running truck, it all matches up.
I unplugged the cold start injector too see if it was flooding the intake, no change.
There is nothing that I can see in the exhaust pipe.
I have gotten on it and tried to get it hot and immediately checked to see if the cat was glowing, and it is not. The exhaust sounds poor though. I cant describe the sound. Ill get a video of how it sounds too. I think my muffler or cat is coming apart inside possibly. But I don't know if that is the problem, it does run perfectly sometimes.

video of revving it for exhaust sound
http://www.youtube.com/watch?v=8GdXb...ature=youtu.be


I realized the truck had a fuel pump that was not correct for the truck. The one in the tank was way to small and the fuel pump screen was completely full of rust/gunk from the tank.

I put in a brand new pump (correct one) and pump strainer.
It ran great for about a day. It then started doing the exact same thing the next day. Issue not resolved.

Put on another brand new fuel filter, still no change. although the inlet side had reddish gas that came out of it. I drove it for 60-70 miles to try and diagnose it or find out another clue. I came to the realization that the tank had sat for a period of 3-5 years before I had it and was probably full of rust.

I pulled the new pump again to look at it. BINGO i thought, the strainer that was only days old was full of rust and gunk again. Most of the thick rusty gunk is in the bottom of the fuel pump "basket" in the tank. I cleaned out the gunk and tried to make sure the tube wasn't clogged (but I cant confirm it is or isn't) I poured some gas in with the plug pulled and got a good majority of the big stuff out, I got a new fuel pump strainer and put in some fresh gas. I thought this would solve the problem based on how bad it looked. Drove it for 3 miles and the problem is back. I know I need to get a new gas tank, but thought a fresh pump, strainer and filter with new gas would at least temporarily resolve the issue if it was the tank.







Im at a loss here. I think my next step is too start chasing wiring problems, and that sucks! I considered injectors, but it seems that if it were them, it would misfire consistently right? not just cut in and out? Any advice would be great. I am off friday and will be working on the truck then. I would prefer to not take it to a shop.

I may have missed a few things I checked, but here are a few pictures and Ill get the video uploaded soon.

http://www.youtube.com/watch?v=3BLEk...ature=youtu.be

Gamefreakgc

If that gunk has been passing through your fuel system, my first thought is that you might have clogged injectors or fuel line blockages as a result. At full-throttle (WOT) with clogged injectors, your air/fuel balance could be skewed enough to make the truck sputter and buck like you are describing. At only partial throttle, they might be still spraying enough fuel to keep the cylinder running, albeit poorly.

Finish cleaning/replacing the tank. As long as you have that going through your engine there's going to be issues, both immediate and long-term. When done, run several injector cleaners and/or Seafoam through your gas tank.

You might even try running Seafoam through your brake booster line straight into the engine. If the rust/grime that passed through is recent, the Seafoam might be strong enough to remove the buildup in your engine.

86STLRunner

Thanks game,
Im going to look into the fuel lines more this week

86STLRunner

Anyone with some more ideas? Gas tank will get ordered this weekend

Co_94_PU

iTrader: (-1)

Don't forget to flush the line between the tank and filter. From the front to the back, while you have the tank dropped. Air will be fine, if you can rig something up with a parts washer or fuel pump even better.

Also inspect the supply line for kinks or other damage.

That looks alot more like dirt and algae to me. Notice how clean it is where it was wiped off and in the sump. You could probably just wash it out and be good to go. Might need abit more refurbishing if there is surface rust. Red-kote, or another tank liner of your choice. Don't forget to get out the inspection mirror and check the top of the tank.

If you can stand it being down for a couple days clean and reseal on the tank will save you some cash. Which you could spend on new hardlines and an injector clean and tune..

INFINITY

does it act like this?
http://www.youtube.com/watch?v=vOdnP...ature=youtu.be
i am pulling my hair out as well.
my fuel tank is clean and i have good fuel pressure and flow.

86STLRunner

Ordered a new gas tank from Rock auto for $80. I called a few shops and was quoted $140-200 to clean and seal my existing tank. It is not worth the time to me to clean mine myself for $80 ya know. It would take days to complete and hours of time.

I also ordered a new clutch master, fuel pump strainer and fuel filter. As soon as the parts get here, I'll start back on it.

atthegates78

Just a suggestion, have you checked you "fuel pressure regulator"? I had a very similar problem with my 86 and just this weekend after many hair pulling days, found that it was the culprit. I just did a complete rebuild on the motor and the truck still fell on its face. I put a pair of vice grips on the return line to the tank, that comes form the regulator, and surprise, runs perfect now.

86STLRunner

All of my parts arrived. The gas tank looks awesome. It's quite a bit nicer then my oem one lol. I also have a new fuel filter and fuel pump stainer. All purchased from Rock Auto. Great website.

I also got new front bumper ends. They were only $3 each! How does everyone now own a new set of these. I also have a new clutch master to install. I will be on it Sunday after my Easter stuff is done.

I cleaned the fuel pump Strainer and blew compressed air through the fuel line and then drove it the other day. Drove perfectly for about 8 miles. Then it slowly started coming on worse. I drove it about 40 miles total. I pulled the pump again to see what it looked like. The fuel pump strainer was already getting clogged with rust! I have a good feeling the new fuel system components will do me a lot of good!

Rouge Runner

I'm having a very similar issue. Mine started after I shipped the runner from Alaska to Washington. I had to drain the fuel tank to ship it and I figured something in there clogged my fuel filter so I changed it. It ran great for about a week and started up again. I went to town with my meter the other day and checked my timing, mag pick up, and ignition coil. everything tested within .2 ohms so I got fed up and left it for the night. I drove it all day today and it runs fine. Be sure to update as to how it runs after the tank/ fuel system parts install.

VAhunter

My '93 pickup had a similar problem. I replaced the fuel pump, strainer, and filter and it was still being a pain. I had taken the intake off so many times i could do it with my eyes closed. today, i took it off again and replaced the fuel pressure regulator and now runs like a dream. If the rust gunk got up into the filter I'm certain it got into the rail and injectors, pull the rail off and try to look through the injector holes to see if there's gunk built up in the rail. Good luck

86STLRunner

Thanks for all the suggestions guys. Ill be doing the work on the fuel system tomorrow afternoon. I will definatly keep the thread updated. Even if the fuel tank doesnt do the trick, I dont feel like I can properly continue diagnosing the truck until I can rule out the tank.



What a cool smiley, I just wanted to use it lol

Ocell

Is it like THIS?


I just spent a couple weeks with what sounds like the exact same issue as you. It turned out to be a tear in my intake piping that goes from the AFM to the throttle body. When I would put load on the engine, the engine would twist in the bay. This movement opened a tear in the elbow that goes to the throttle body. That would let in unmetered air and kill the engine.




https://www.yotatech.com/forums/f199...l#post52060197

Try cranking the truck and tug on the intake assembly side to side while it's running. If you can get the engine to bog take it all apart and check for tears/cuts/holes!

I hope it's your issue too. It's a super easy fix.

86STLRunner

It's been a while but I'm back into working on the truck.

I've replaced every component of the fuel system. I thought I had it nailed.

Wrong, it fell in its face after 3.5 miles and I started thinking it could be the distributer. I feel confident the spark and fuel are all brand new, except distributer. I swapped it out with highlux's known good one and it ran perfectly for 26 miles theeeennnn it fell on its face. This is getting frustrating.

Anyone with any ideas?

SoCal4Running

Look into plugged exhaust.
When my Cat went it actually killed the motor while I was driving down the freeway. Coasting down from speed I dropped the clutch at about 50mph in 4th and it started back up and I could see all kinds of bad stuff shooting out exhaust pipe in rear view.

For home and pulled the Cat out and it was HOLLOW inside!

SPARKS89

iTrader: (1)

Drive with your TPS unplugged and see if it still does it. It'll put your truck into 'safe mode' so the air/fuel mix won't be optimal, but it's an easy way to tell if your TPS is bad. I know you said it's ohmed to spec, but I had the same problem with my truck earlier this year and it turned out to be a brand new TPS that was bad.

86STLRunner

Ive been thinking exhaust. My muffler is definatly bad (it sounds like its rusted inside and has visable rust on the outside of it) I have a new muffler, just need to get it welded on. Ive unplugged the tps and thats not it.

this thing has me lost. Ive checked everything you would normally suggest. I can never get it to act up when i want, and defiantly never in the driveway. it runs perfectly in the driveway every time. but you get out and it will fall on its face and kind of sputter power. i will push in the clutch and shift, keep it at 1/2 throttle or less and i can usually regain power again. but i almost didn't make it up a hill that is no problem usually. it was having a bucking fit and i had to ease her up slowly.

FWIW, it seems to never do it cold, it is almost always at least 2-3 miles before it acts up.

86STLRunner

had the muffler and tailpipe replaced today. old muffler was full of rust.

didn't fix the problem, but its one thing off my list.

Jbowls

Same thing happened to my 91 4rnr. Drove it early this morning it was ok.... Timing seemed off even though it checked out on timing light. Been that way since rebuild 600 miles ago. Everything is new. 60 over 268 cam decked hd rockers and springs over sized valves.... But on the ay to the shop for my 500 mile service to re-torque head and valve adjustment it started sputtering after warm-up like it was not firing on all 4. I inspected then continued to the shop after not finding a problem. Guess ill see what happens. I'll let you.know what I find out

Jbowls

. Bad injecter...