Tom928

I recently replaced my vacuum hoses and after getting things back together there is a significant hesitation. This occurs mostly at about 1000 to 1500 rpm and if I slowly push on the gas pedal. If I push hard on the gas, there is no hesitation but I can feel it struggling as I accelerate.

I did a search in the archives and the the main cause looks like vacuum leaks. I rechecked the vacuum lines to make sure I didn't miss something and it looks good and holds vacuum in the new lines.

One item is that the inside diameter of the new hose is much smaller than the original - could this be causing a starved condition or a decrease in vacuum at low rpms?

I appreciate any help,

chrly924s

My 83 does the same 'struggling' thing. I can smell gas around the right front fender. If the Y to the charcoal canister is broken, can this cause both symptoms?

Tom928

Chrly924s - are the fuel lines in good shape? They come up to the engine compartment on the right side.

I don't have the gas smell, just the hesitation and struggling.
I am considering replacing the "replaced" vacuum lines with ones with large I.D. to see if the smaller diameter is causing a vacuum starving condition at lower rpm's.

Mongo

What did that smaller diameter hose you replaced lead to?

Tom928

Hi Andy,

Well, I replaced both distributor lines (retard and advance). The lines to the fuel pressure regulators and damper which has a T for one line to the throttle housing. Then one line to the diverter valve. Also replaced the blue/black vacuum check valve.

Thanks,

chrly924s

They are hard as rock. That is the next thing on my list (I got shocks waiting to go on and the vac line kit) Any suggestions where to get these fuel lines? I don't need racing quality.

Dennis Wilson

It sounds like the retard and advance lines to the distributor are reversed.

Dennis

Tom928

When I swapped lines here is what I found;
The retard line goes to the front of the throttle housing
The advance line goes to the back of the throttle housing.
That is how I replaced them.

Dennis Wilson

Are they on the distributor correctly? The retard goes on the flat side and the advance goes on the convex side of the unit. If that is correct, have you checked your timing (with the vacuum lines removed and plugged)?

Dennis

PorKen

If the vacuum line has vacuum at idle, it's manifold vacuum, which is the retard. The retard barb is on the inside, facing the distributor, the advance points away.

The ID shouldn't matter. It may have a slightly faster response with a smaller ID.

The stumbling sounds more like it's going lean. How many turns out on the AFM bypass? (Screw it in all the way, and count the number of complete turns. Max = ~14) For emission checks, I set my '81 to 6 turns out. For regular driving, with a free flowing exhaust, one turn. I would try two or three, and see if it gets better.

Tom928

Thanks Ken - I went and checked the AFM bypass and it was 1/2 turn until it was in all the way! I gave it 2 turns out from that point and took a drive. It started out still stumbling; however, after a few minutes it stopped and the struggling at higher speeds is gone. I gave it another turn (total of 3) and it runs much better now.

I can find the engine idle speed, CO level and O2 sensor checks, but is there a AFM check or tuning procedure or is pretty much by ear?

Thanks again,

rjm65

Sometimes cheapie silicone vacuum line can collapse under vacuum... as I found out. Might not be the case here, but worth mentioning.

markwoodlief

New owner of a 86.5 928 and was wondering where that AFM bypass is located? I am ordering up the service manuals but wanted to get a start on making some adjustments now. I'm having the same issue actually so wanted to try the AFM as well....

Thanks!

heinrich

yes, this can happen

marton

When I replaced my vacuum hoses I had a stumble afterwards.
Eventually found that I had somehow kinked the rubber gasket on the inlet that the plenum (or air intake) fits into; had to pull it and reinsert then it was OK.
You can see it with a strong light peering in from the side....
Worth a mention.

Marton