Tamaren

I'm still fighting an acceleration problem. A hard acceleration is fine, but on normal acceleration it is.. choppy? It'll studder a few times.

I have replaced the entire fuel system tank to injectors, fuel pump, all regulators and dampers, all injectors, exc.

My plugs are a little white, so that leads me to believe a little lean, and I have a little bit of temperature rise, as well as this problem.

I replaced all vaccum lines, and I hold 16 in. Of vaccum at idle, however my brake pedal is pretty hard- which is a bit of a concern.

my plugs are new, so is cap, rotor, wires, exc.

Ive replaced every engine part that I can think that would effect that performance. What am I missing? is 16 in. Too low? Should I look at my brake booster?
Ive gone through every forum and worked through all of them- I can't find the answer.

My next step without any answers is tying into the barn door sender or an L-jet brain.

Car is an '81 5 speed.

Thanks!

Speedtoys

Have you checked your A/F readings at idle with the O2 sensor disconnected?

My 83, after adjusting the AFM pot, ran MUCH better.

I wanna say, section 24 of the WSM...

rjtw

Yes. What he said.

Other thoughts: I have no idea if 16 inches is good or not, but ensuring you have no vacuum leaks is a good idea. One culprit I've found in the past for stutter on acceleration is a leaky O-ring between the AFM and the U in the intake.

After you've run down the WSM list, if you still have issues you may want to check the pot in the AFM as Speedtoys just mentioned (yours is L-Jetronic, right?) The wiper can wear grooves in the pot over time and, if worn too much, can cause incorrect A/F mixture typically at midrange RPM and throttle but usually OK at high power (because the tracks are worn the most in the middle and less as the barn door swings to full open). I just opened mine up and reset the wiper tracks, you can find more info here, and also google youtube: https://rennlist.com/forums/928-foru...fications.html

Cheers,
Rick

SeanR

Sounds to me that you have an air leak causing it to run lean and that the AFM may be out of adjustment. Have you changed all 8 of the runner rubbers and the throttle body rubber and o-ring?

I've found one of the intake runner rubbers folded underneath, where you can't actually see it and just that amount of unmetered air can cause havoc.

Tamaren

All good thoughts- the thing about the barn door is I have to drill out the plug to mess with the mixture, which I'm not opposed to doing but it doesn't sound fun.

i have good vaccum, and my spider boots and o ring are both brand new.
My next step will be opening up that barn door to see if there is any problems with the track in there. That sounds like my problem.

i will also look at the WSM and see how to adjust the pot

Guy

I don't think 16 inches of vacuum is good. My 79 pulled 20 and still had a sizeable leak. Of course, other factors affect this but I mention it for conversation purposes.

I used a smoke machine to find my vacuum leak. Took all of 5 seconds and 65 dollars. Best money I ever spent.

Speedtoys

That plug may just fall out...

Or hold it from spinning with a pick, while you drill a shallow hole for a sheet metal screw to bite in it..and pull it out.

granprixweiss928

these cars are that way somewhat. I fought this issue for a year....getting the car in good proper tune is the key.

unplug o2 sensor, does it go away?

install a wideband and see what is going on.

Tamaren

Nope- Already went through that when I replaced the 02 sensor. Same thing both times.

granprixweiss928

here is my thread for reading

https://rennlist.com/forums/928-foru...ing-ideas.html

granprixweiss928

Ive found that the richer it gets, the worse it gets.

Tamaren

Okay, been a week and done a few things.

Slightly richened it, and dug into the barn door, everything looked okay, I went very rich to start, then worked it back down to "pretty close"

Still unhappy.
I haven't replaced my injection relay yet, so I'm doing that. My wires, distributor and rotor are fine.
I haven't done coil, or ignition module, which could be a problem.

I also haven't done my L-jet Brain.

I know everything as far as vaccum is fine, the only thing that could possibly be leaking is the Brake booster, which I will test.

I'm running out of things to replace, and it's starting to make me mad. any help would be appriciated.

Guy

At the risk of being repetitive, 16 inches is too low. You have a vacuum leak. I too, scoured my engine bay for many days looking for leaks and was resistant to the suggestion that I missed something but guess what, I did.

Tamaren

I will continue tracking today, I guess. HVAC holds vacuum when I test it, so that doesn't sound like the problem. All prehiprials seem to hold vacuum in the fuel system, as well as dist.

I'm going to test the brake master cyl. and see if that is a problem. It might just be easier to smoke it.

Is there any other vacuum lines that go crazy places that aren't obvious? It has to be a large leak, so you have me worried that there is an entire hose disconnected or something.

(I guess I could just follow the diagram.)

928NOOBIE

+1 My car is an '86 but the folding under of the intake runner rubbers is one for me and on my car at least for some reason it's really easy for those things to fold under and you have no idea. The fold under always on the underside...and the pipe-organs are nearly impossible to see under on all cylinders.

Also yes it sounds like it's lean...running lean makes them run warmer