mervynp

Hello,

My name is Steve and I have a vacuum problem.

How do I know I have a vacuum problem? Because I own a 928.

But seriously, I did a vacuum refresh on my 86.5 Automatic using the kit from Roger, which was great and very easy to use, but I still have an issue that is affecting the running of the car especially when cold. Until the engine gets warm the car has little or no power and does not pull, it feels like it is in limp mode, smells rich as well. Once warm it still doesn't feel like it has full power (according to the highly scientific but somewhat uncalibrated butt dyno) but is much stronger and smoother, especially at idle. When I was doing the refresh I found the valve clamped to the strut brace was faulty and replaced it, but it looks like I have missed something else as well.

If I put the mityvac on the vacuum pipe leading to the EZF I get about 16mm of vacuum on idle when cold, when I rev the car the vacuum drops but after a couple of seconds recovers to steady state. When I let the revs drop, the vacuum spikes but then recovers in a similar time. When warm the behaviour is similar but steady state is stronger at 20mm. Is this normal, I am guessing not? I also get occasional hard shifting, especially when cold, when driving in the delightful Bay Area Traffic.

I am pretty sure I got the wiring right, Rogers diagram is pretty clear and simple to follow if you do it one step at a time, even for a duffer like myself, but I am beginning to wonder if I did something really daft like put the wrong lines on the wrong TB connectors. I also have an inkling that it is something to do with the thermo switch and/or valve mounted in the wing that comes off the carbon canister, how would I test these? I checked the Y connector and it is sound, the PO (bless him) have attempted to block the system off with a bit of masking tape which I removed.

I know I know, I should do a top end refresh, I am pretty sure my breather hose is less than secure and the valley is full of oil, fuel lines look like they have been replaced at some time and are good so no danger, but I just don't have the time right now. I have tested the TEMP 2 and TPS switches, all good, adjusted the throttle cable to remove most of the slack and so far my ministrations have gained me at least 4MPG and doubled the power (again, measured via butt dyno), it is my daily driver and we have a new baby on the way (see above re time) so need it to be reliable.

PorKen

You might want to change the title from 'pt 94' to '86.5'. I only clicked on this thread by accident.


I think you mean 16 inches mercury, IE. 16" hg, not mm. Normal idle is usually 18-20".

Check that the line to the trans holds vacuum. The FPR, or dampers may be leaking. Check those as well.

How many miles on the MAF? If >100K then it is due for rebuilding.

mervynp

Errr, let me have a play with title threads, not sure how yet.

You are of course correct, I mean inches, brought up on the metric system is my excuse.....

MAF is probably due a rebuild, FPR and dampers hold vacuum at greater than 20 inches if I just pump them individually, ditto the transmission line, it is just the system as a whole that is low and then better when warm.

Any thoughts on the transient behaviour, is this correct, I can't think it through?

pjg

Are all spark plugs firing ? Use an inductive timing light on each plug wire to check. Look at the plug wires in the dark and check for arcing to ground.
Are all injectors clicking ? Put a wooden dowel from each injector to your ear and listen.
Pull spark plugs and inspect for normal condition. Check distributer cap
and rotor, if all cylinders are not firing you will see low vacuum.
Is the brake pedal stiff all the time ? Could have a leaky brake booster. Just a few of the endless possibilities

Look here for spark plug info: http://www.ngksparkplugs.com/tech_su...qs/faqread.asp

Maleficio

If you had a bad vacuum line to the tranny, you would be experiencing very hard, abrupt shifts.

PorKen

Your symptoms could be caused by one or both cams being a tooth off. (It's easy to do when stringing the belt, if you don't pull the belt tight.)

7.5° of cam retard on one side will make it sluggish, and have weird vacuum. Both sides advance a degree or two as the engine warms up.


(Click the to edit a post/title.)

fraggle

Check the charcoal canister bits under the passenger fender. Lots of opportunity for leaks that can be intermnittant due to cycling of the vacuum valves.

mervynp

Thanks for all the suggestions (go advanced on the edit button found the title field).

The plugs are all good from inspection, no sparks, I don't have a timing gun but I can borrow one and check that they are actually getting current, if I measure the vacuum off the feed from the brake booster for the aircon/cruise it is as good as anywhere else, I have not checked that part of the system, so that gives me a good excuse to duck out of christmas for a few hours.

I had not even thought about cam timing, but I think I understand how this might work, is there an easy way to check this? I also need to have another ferret around under the front fender, perhaps the POs attempt to block the carbon canister off is more of a clue than I thought.

Cheers,

Steve

Mike Frye

Did it do the same thing before the vacuum line replacement?

Maybe the issue isn't vacuum at all. I don't like to start down a road by saying, 'I have a vacuum problem, let me exhaust all of the vacuum options.'
I think the way to go about it is to isolate what you know is true and restate the problem.

The problem is really that you have less power cold than hot, right? And it's sluggish and shifts bad sometimes but not always.

This may be vacuum or vacuum related, but it could be something else or both.

The other top issue with these cars right along with vacuum is electrical issues. Have you checked the O2 sensor? My car was doing all kinds of weird things including hunting idle when cold and high idle when hot and it turned out to be the O2 sensor wire working it's way loose inside the plug (someone must have pulled the wire to unplug it instead of the plug).

I'd go through the whole test plan and try to isolate where the problem is (or problems are).

Make sure you have no intake leaks (common) make sure you get the right readings at all the sensors (and back at the harness) and also see if you can isolate the variables (RPM related, time related or temp related, how long does it take to go from really sluggish to a little sluggish, etc).

mervynp

Mike,

I know what you are saying, and I am under no illusion that the vacuum is the only problem, but I am pretty sure what I am measuring is not correct, so had better start there. It was doing this prior to replacement, in fact it was way down on power across the board and the shifting was always harsh, so I feel I am winning.

Electricals is the other thing I have been pursuing, checked and clean all the grounds, found one that had worked loose/been disconnected, which has helped a lot plus a bent ground pin on the LH plug that was causing an intermittent start issue, now fixed. O2 sensor could probably do with a retest as I think I did it, but can not swear to it, perhaps I've missed it as I am not the most methodical of people. Other sensors check out and I did get rid of several intake leaks already, but perhaps I need to test more thoroughly.

Again, much appreciated to all,

Cheers,

Steve

Mrmerlin

plug the vacuum port for the HVAC and see if the vacuum increases,
Vacuum port connection should be next to the brake booster its the black line leading to the firwall
if so then you have a leak in one or more of the vacuum pods in the console.
Replace the temp 2
install a fresh MAF,
check the timing of the cams

rexpontius

sound pretty similar to my 86.5 when I got it, the PO mounted the MAF upside down.

Maybe small chance, but I would check it anyhow.

JHowell37

If you're holding 20" of vacuum at warm idle, that's as good as it gets. Even at only 16" of vacuum, the loss is not so severe that you'd notice some of the symptoms you've mentioned. It sounds to me like your MAF is in need of repair.

mervynp

Oh My HVAC definitely does not hold vacuum, but there is an isolator between the brake booster and this system, which is sound, perhaps not very sound so I will plug that, five minutes work and can not hurt.

New MAF in the new year sounds like a good plan, and thanks Rex I have taken it off and put it on a few times, I could have screwed this up! I still think the transient behaviour is odd, so I'll check the timing as Ken suggested.

Thanks for everything, I'll update you if/when I get this sorted....

Steve