1987 4+3:
This is especially bad when the car hasn't been started in a while. If I press the accelerator more than just a little bit, the motor will stumble and sputter for a few seconds (~2-3). If I release the accelerator, RPM will drop and then it will balance out... until I give it some more. Every now and again it will stall completely if I don't remove my foot from the pedal.
I tried an experiment last night when it was doing this; if I slowly and very gingerly press the pedal, RPM will increase smoothly, but any abrupt introduction of the gas pedal will cause it to stumble...
After the motor has run for a few minutes, this condition gets less severe.

This sounds to me like a fuel delivery problem. Does that sound right? Maybe there is a problem with my fuel pump? It's not low fuel level causing the problem either cause it will do this even with a full tank of gas. Perhaps injectors? But could all of my injectors really be that gunked up? Or would it necessarily(sp? I hate that word :crazy: ) have to be all of the injectors or could just a few cause such a symptom?

Fuel filter has already been replaced but the old one wasn't too bad.

Ideas?

 

Could be clogged injectors, poor spark, low fuel pressure, etc. Have you tried any injector cleaner yet? Techron from Chevron works very well if the injectors arent to far gone. That will only cost a few dollars. Try it and see if it gets any better.

Watch the engine idle on a very dark night. If you see spark jumping from the wires change em. Bad wires will cause a lot of problems.

Fuel pressure should be around 40 PSI if I am not mistaken. (I am not sure)

Good luck.

 

you may consider replacing the fuel filter first and foremost.

 

Does sound like fuel (though it could be a vacuum leak, dirty throttle body or air getting into the intake after the MAF) as if it's getting better after it warms up, you're going closed loop and the O2 sensor is helping smooth things out. Do you have a scanner or a fuel pressure guage? It would be easier to diagnose if you could post fuel trim values while in closed loop and pressure. What do you mean by "the old fuel filter wasn't too bad"? If there was any grit on the output side, that could spell trouble, but more info would help.

 

Mine does this when she's dead cold, and I've replaced.......

Fuel Filters
Spark Plugs
Plug Wires
Rotor
Cap
Control Module

....she also has strong fuel pressure across the board. I think I will clean the TB for the sake of doing so. After 3 minutes of driving all studdering goes away. I don't typically go over 3000rpm until at least the coolant has reached 120 degrees anyways. Just be ginger on the gas until it warms up a little. Also, keep your foot ON the throttle during the shift (like a mini-powershift), this helps out emensely.

 

scorp, you ever run diacom to find out what your mixture is at idle? almost sounds like your rich at idle which could be a couple things. #1 if you have 24lb injectors & didn't burn a new chip. high fuel psi...this is just a guess as i'm running 52lbs & still lean at idle. sounds like when your 02 warms up everything is under control but before it's on the rich side. almost wonder if a 3 wire 02 would be a easy fix to get signal to your ecu quickly since a few mods may have made you a tad bit rich.

 

almost forgot one other thing i was about to mention, if your still on the stock prom and stock injectors you might pick up some of the ford 19/lb injectors on ebay for $50 a set or so. people give these things away and if you have 150k on yours...things could be leaking slightly? again just a guess but at your power level a 19lb injector at high psi would spray really nice & perform like a champ.

 

Thanks for the comments. I haven't done a diacom run yet to check out the mixture. Fuel pressure is a constant 43psi at idle.

My injectors are still the stockers, and I have not adjusted the FP at all. The only thing shooting out of my tailpipes is a small bit of oil thanks to valve stem seals. I dunno. :) I might pick up a second set though and have em' cleaned/blueprinted for the heck of it.

Thanks.

 

Well I've replaced:
cap
rotor
coil
ignition module
plugs
wires
fuel filter
and I recently did a bit of work on my intake: replaced damaged air-filter housing with one that I repaired, replaced stock lid with an open lid, and replaced paper filter w/ a K&N.

I had the problem before all of this stuff and it still persists after... These were all done because they needed to though and not to try to fix the studder though I was kinda hoping that it would :)

I hear crazy talk that there are 2 fuel filters is this true? If so then I only replaced one of them. I don't think I have a tool to check fuel pressure but I'll try to check it somehow and report back.

I have tried injector cleaner but it didn't solve the problem...

By "the old filter wasn't too bad" I mean I blew on the end of the new filter and it wasn't restrictive and I also blew on the end of the old filter and it was only slightly restricted...

 

My low rpm studder was a vaccum leak. It was worse at cooler engine temps but was still prevelant as it warmed up but not as bad. Then agian, my leak was huge.

 

You calling me crazy? :)

I first reported the 2 fuel filters probably around 6 months ago. On my '87 there is a feed and a return fuel filter. The feed one is the "normal" one we all change. The return one is directly above it when you are under the car, and screws on like an oil filter. :)

Even Jeff Kopp didn't know about it until I emailed him asking for a new one and he looked it up. :D

 

I changed the fuel filter on my 88 this summer and never noticed a second filter under there. Is that just on the 87? Or did I miss it on my 88?

 

Are you denying it? :D

 

I have no idea. It's on mine, thats all I know. :)