Tdubbs05

when i made my trip out to AZ from the bay area in CA, i noticed some random studdering when i'd gradually speed up. it was almost like the car gasped for a second cause it wasn't getting fuel, but what do i know. i decided to order a fuel filter no matter what but i wanted to know if it definitely was the fuel filter that was causing that issue. (the fuel filter hasn't been replaced yet) any thoughts?

pepsibluefloat

I had a similar problem with an f-150 i had. One of the tanks had a bad fuel pump, so whenever i used that tank i couldn't really accelerate well--but i'd be able to maintain speed once i got there.

Tdubbs05

good point. but it's not very consistant which leads me to believe that the filter is getting clogged for a second everyone once in a while.

1stgenrnrdude

how long has it been since you replaced plugs, wires, etc.? because my dads was having a similar sounding problem, and it was just mis-firing

BC Rider

I'm in the midst of trying to sort my 3.0 with similar symptoms.

I have not replaced the fuel filter yet, as I think it is a bit of a long shot, and the banjo fittings have not been moved in 17 years - so it won't be easy.

So far though I have found that disconnecting the EGR (just remove the top vaccuum hose from the top of the EGR valve) does make it much better. It takes about 30 seconds to do this, so you may want to try it.

This leads me to think that the EGR VSV is maybe a bit off ---- or that I have too much backpressure from the exhaust.

I'm speculating here, so would appreciate feedback on whether my thinking is off - but a snafued EGR could intermitently dilute the mixture going to the engine resulting in a bit of a surge/shudder.

JEBSR5

BC
I did the same as you on EGR and my shudder/stumble went away also. Correct me if I'm wrong, but if it was exhaust pressure, would it not still do it with vacumn disconnected? Been trying to wrap my head around the cause of this also . Would like to connect it all back up as it is beneficial to use. I had thoughts that it may be the vacumn modulator or valve I unplugged it from. Haven't gotten to testing yet.

BC Rider

JEB:

I'm speculating that if your exhaust is restricted you have higher pressure in your exhaust manifold (or wherever the egr get's it's source).

Then when the egr opens, you end up getting more exhaust gas in the intake than you should due to the higher pressure pushing it through the egr. Therefore it makes it leaner than it should.

Like you, I've yet to fully inspect and test my vacuum control hoses, vsv etc. - so my pressure may be normal. But my initial checks (low vac at low rev, high vac at high revs) at the egr modulator indicated it was working OK so the vaccuum signal to the egr was looking OK. What I did not know then (and know now) is that low vac is defined at 3", and high is around 13" - so I'll be rechecking it.

Here is a document with some of this info in case you haven't seen it before

http://www.autoshop101.com/forms/h61.pdf

JEBSR5

BC
I see where you are coming from now after reviewing the pdf file. Also note the area in pdf where modulator is key to EGR operation, so the problem may lie there as I initially thought. I also realise that any other of the ports could contribute to the problem, so just replacing modulator is not an answer until I can determine each port is functioning properly. If i'm reading correctly, the modulator should adjust for back pressure. Of course, if I had a spare modulator, that would be a quick test. Ah, but I don't. I suppose I'm anal about trying to reason through each aspect to determine the problem, but that's just me.
Hope to figure it out soon, like the fact that the EGR keeps cylinder temps down.

OOPS! I think we are hijacking this thread, well guess not as it does apply to the problem.

imspidey

I have an '81 4wd beast....I get up to any cruising speed and then the stuttering starts until I accelerate again..it has a new fuel filter...any suggestions?

se7enine

iTrader: (2)

Any codes?

imspidey

havent checked for codes honestly...not too knowledgeable on cars other than the basic stuff....wasnt aware there was en ecu on this early of a rig

91gen2runner

I have all those same 3.0 issues, found that my egr is all clooged up along withe one of the steel tubes over the engine, now replacing them and the 02 sensor, might do cat to. Did you guys ever figure out what yours was doing, think the vacume idea is the best, im hoping

James Woods

iTrader: (1)

There are no codes to check on an 81, so you changed the fuel filter but what about other things like plugs, wires, cap and rotor? Try doing a seafoam clean, just start with the simple things first and then go from there, also since you have a completely different motor and fuel system, I would suggest starting a new thread.