Stumbling off idle

[Terry]

I have been driving my 86 to death for the last few years. I have had an issue for a long time, that when I warm it up during winter it loads up. If I rev it to where it stmbles bafore I talke off it will clean itself out. Last night on my way home it started stumbling off idle everytime. The front fuel punp sounded different also? I don't know a ton about fuel injection. I have been working on air cooled VW's for a long time so I know carbs. I have a code reader and the last time it threw a code for the O2 sensor. I need to fix this issue as well a do a "complete" pm on my injection system. Can someone help me with this issue as well as give me the lowdown on how my injection system works. I know that it runs in open loop until it warms up then goes into claosed loop but that about it?

 

[MAKG]

Unlike VWs (I got a Digifant II), you have a set of self tests you can run. And you don't need a VAG 1551 or anything else more fancy than a test light and paper clip. But I suspect this isn't your problem.

Just like you would on a VW, look for a rich condition. Inspect the spark plugs. And pull the fuel pressure regulator vacuum line to see if it has fuel in it or doesn't hold vacuum. Do that last part first; it's very easy and fairly likely. If you find fuel, you need to replace the FPR, as it is definitely blown. It will cause #3 and #6 to run ridiculously rich, possibly to the point of missing. If it does miss, you can get lean codes (even though it's rich missing), and the rest of the spark plugs will run rich as well to try to compensate.

If you have two cylinders missing due to outrageous fuel, you can very easily stumble as soon as you try to put any load on the system. You then blow the accumulated fuel out the tailpipe as black smoke (or into the crankcase!) and it runs OK. It's very difficult for the driver to see the puff of black smoke, but the guy behind you can often see it.

Only one '86 in existence has a factory check engine light ('cause I put it there, stolen from an '87), and I don't think it's on the road anymore. But you still have self tests you can run.

 

[Terry]

MAKG,
Thanks for the info. I did not think that I was going to make it home tonight. I stopped at the light and kept it reved up above idle. When I took off from the light it stumbled and almost acted like it was running out of gas. I pulled into a parking lot and drove around a building back to the street. It cleaned out? If it was carbs, I would look at the idle circut as well as fuel pressure and or float? I have been looking at other peoples postings on fuel related issues and it seems like some people just throw parts at the issue until they either fix it or take it to the shop. I'm not into working on cars like that. I am going to go thru the book and do one step at a time? Figures now our weather is turning to crap.

 

[El_Capitan]

Yes thank you for the info too! I too was dealing with this same problem, only I didn't make it home tonight.. After towing it home and checking this site I found this in the forums, I checked the regulator and what do you know, gas ran out of it! Thanks again for the info

 

[Terry]

Does anybody have pics of the FPR? Mine does not look like the ones that I saw on line?

 

[Terry]

Went out and pulled the vacuum line off, there was no gas commig out but the damn hard plastic line broke. Went to habor freight and bought a fuel pressure gauge and a vacuum guage to test this thing and a fuel pressure regulator. If I am going to mess with this thing I want the correct tools and be able to do the job and know that I fixed the correct thing? Now I need to figure out how to Christmas shop for the kids and fix my truck at the same time?

 

[Terry]

I have a few questions. The connections to the FPR don't look like a regular hose clamp. Do I use the fuel line removal rings? Where do I put the fuel pressure gauge? Do I check it at one rpm or go thru the rpm range?

 

[MAKG]

There is a Schrader valve on the fuel rail -- it's pretty easy to see on a 2.9L. That's where your fuel pressure gauge goes. Fuel pressure is a function ONLY of throttle position, not RPM (and having the engine off is equivalent to full throttle).

You can replace those vacuum lines with bulk emissions hose. They break all the time. If you really want to, you can use emissions hose to patch it (BTDT). Their only advantage is that they don't flop around like rubber hoses do.

Why are you replacing a fuel pressure regulator you don't know is bad? You're wasting time and money. It could be quite literally hundreds of things (many of which are wires), so stabbing in the dark is just going to make you poorer and truckless.

If you're jumping to conclusions, you really will be better off at a garage.

Have you inspected the spark plugs and run the self tests?

 

[JOKER86]

there is a shcrater valve like on a tire on the fuel rail and u can check it at idle and if possible check it under a load while driving. which connections are you refering to btw??

 

[Terry]

The auto parts store is 25 miles away and at 25 degrees and snowing the 48.00 I paid for a part I will have when I can get to the truck sounded good to me? I did not say that I was taking the shotgun approach and changing it, I want to be ready with from what I have been reading here sounds like goes bad more than most other parts? When you live rural, you need to think about how far it is to the next bad part? I did not think that this was a pick and pull part or I would have gone there 40 miles away and pulled more parts? Joker, I am referring to the connections to the FPR?

 

[JOKER86]

The auto parts store is 25 miles away and at 25 degrees and snowing the 48.00 I paid for a part I will have when I can get to the truck sounded good to me? I did not say that I was taking the shotgun approach and changing it, I want to be ready with from what I have been reading here sounds like goes bad more than most other parts? When you live rural, you need to think about how far it is to the next bad part? I did not think that this was a pick and pull part or I would have gone there 40 miles away and pulled more parts? Joker, I am referring to the connections to the FPR?

i have a replacement FPR on my 86 and it comes with regular hose clamps but i think the stock ones are a one time use item, im not sure because its been about 2 years since i put mine on so i cant remember what the originals look like, but there are spring lock connectors about a foot from the fpr if im not mistaken.

 

[Terry]

Got some better weather and time to work on the truck today. Put the fuel pressure gauge on, thurned the key to on. After I fixed the gauge leak it went up to 40 psi. When I started the truck it ran for about 20 seconds or so and dropped off idle. The gauge was going nuts at almost zero pressure. Thast when the real fun began. I decided to start with the basic stuff and change the fuel filter being that I have not changed it in 3 years. Went to Kragen. The person there said that there is 2 different filters, an inline one and a cartridge style. Put the truck on the jack and climbed under. After I moved the cover out of the way I found the cartridge type. I worked at getting it off using alot of choice words and could not get it off. My book did not show this type of filter, so after I figured out how to pull the lines, I removed the whole filter setup from the truck. Now I need to take it to work and put it in a big vise and unscrew the cover? Anything I should know about taking the cover off etc...? I left the pressure gauge on the truck and went out later and it is still at 40 psi?

 

[IMenriched]

Got some better weather and time to work on the truck today. Put the fuel pressure gauge on, thurned the key to on. After I fixed the gauge leak it went up to 40 psi. When I started the truck it ran for about 20 seconds or so and dropped off idle. The gauge was going nuts at almost zero pressure. Thast when the real fun began. I decided to start with the basic stuff and change the fuel filter being that I have not changed it in 3 years. Went to Kragen. The person there said that there is 2 different filters, an inline one and a cartridge style. Put the truck on the jack and climbed under. After I moved the cover out of the way I found the cartridge type. I worked at getting it off using alot of choice words and could not get it off. My book did not show this type of filter, so after I figured out how to pull the lines, I removed the whole filter setup from the truck. Now I need to take it to work and put it in a big vise and unscrew the cover? Anything I should know about taking the cover off etc...? I left the pressure gauge on the truck and went out later and it is still at 40 psi?

Yes, to that it unscrews...pretty coarse threads. You'll have an advantage having it off....as you discovered not very much room.

more importantly.... the hard plastic is not very thick and will not take kindly to very much abuse. on mine anyway...there was some very shallow notches on the bottom, about every 90deg ...do not take a screwdriver to tap on them to loosen it. better off getting a oil filter wrench...that way pressure points to remove is distrubted all the way around.

If the filter was bad....before hooking the filter cansiter back up...take moment to stab a short hose into the fuel line place it into a small contanier. BTW...some of these had 2 filters one in a cansister, like what you discribing just after the tank, and another after the frame rail pump up by the bell housing/starter area.

remove wire to the frame rail pump...no need to have it run...just remember to hook it back when finished.

may want a buddy to help with this. 1 to cycle the key and another to watch the hose.

do not fully start...just turn the key on...this will flush the line out and help determine the condition of the in tank pump. just a second or 2 with the key on and shut off. If some real gunky stuff is coming out then repete until it clears. if the stream is steady with no interuptions and the pump doesn't sound growly...then it in all likelyhood is fine. If it doesn't sound right or spits & sputters a stream.... well you might be looking at the in tank pump. make sure it has enough gas in the tank, sorry had to say it.

 

[Terry]

Ok, I have a few more questions. My sending unit went down with ship a while ago. Do I buy this or the other pump new or pick and pull? If I need to do the tank pump,can I drop the tank and do it Removing the bed is not something I wnat to do.

 

[IMenriched]

Ok, I have a few more questions. My sending unit went down with ship a while ago. Do I buy this or the other pump new or pick and pull? If I need to do the tank pump,can I drop the tank and do it Removing the bed is not something I wnat to do.

I think most in tank pumps comes with new sending units....that being said, you'll prolly have 1/2 a dozen folks telling you you can get indivdual units/componets.

you certainly can try one out of salvage yard...but concidering what you'll go thru to change it, money might better spent on new. unless you know of a donor that was just replaced.

auctually removing the bed is better than dropping the tank. It sounds like alot...2 avergage fellas can pick it up and set off to the side. Just the 6 bed bolts and filler neck and unplug the taillights from the main harness.

the distinct advantage is....everything is open from the top. Hence no laying on your back and having dirt, grit and parts of road kill falling in your face.

you of course can take the tank down, if that what you got you heart set on. remove the skid plate and tanks straps and the filler neck hose...gentally drop the tank and unplug the hoses and electrical...then slide it out.