924Board.org

[Slam]

Mandy's 924 bogs - badly. Once in motion it seems to run fine. Here's what I've done:

New AAV. Replaced connector to AAV and rewired it in from connector 'T' in engine compartment. Now it's working properly - the idle doesn't drop when I pinch the hose shut warm but does cold. Okay...

Rewired connector for pressure regulator as above. Its connections were bad.

Cleaned ground pin for above and made sure it was grounding properly.

Re-routed vac advance. Wasn't getting much vacuum at front of throttle body (almost nil) so moved vac hose to back of throttle body where I had better vacuum.

Adjusted idle screw. Now the car's not getting false air and the AAV isn't messing things up, I was actually able to adjust the idle!

Fuel pump runs fine.

I did post some of this in another post but I figured I'd start a new thread because the issue from the last one has been resolved.

Yes, I've read the tech FAQ, and I've got the Haynes and Forbes Aird CIS books.

Ideas?

Could be as simple as distributor advance, but the vac advance works - I know because disconnecting it causes the idle to drop.
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'88 944 Auto - may or may not resurrect

[Chrenan]

During this work, did you rotate the distributor at all? Could it be ignition timing?
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1987 951 - M193 Version for Japan

[Lizard]

you should not get ANY vacuum to the advance for the distributor at idle, the vacuum line which runs from the throttle body to the vacuum advance is only supposed to supply vacuum upon opening the throttle, not having MAP pressure.
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3 928s,

[Slam]

All righty then. I'll move the vac advance back to where it was. Thanks, lizard. Chrenan - nope, didn't move the distributor at all.
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'88 944 Auto - may or may not resurrect

[leadfoot]

adjust your timing whilst your at it... make sure you pay attention to whether the distributor hosing is supposed to be connected/dissconnected for this. You want to have the maximum advance allowable for your engine/fuel octane combination...
There are usually three markings on the flywheel the middle one being zero degrees TDC with the other ones either side representing -10 and + 10 respectively... make sure you time off the right one for your engine too. If you run better quality fuel you can advance it from this a little with no adverse reaction, these engines like advance.
Try to have the throttle bypass the last thing to do on your list as a big opening for bypass and low advance will still run warm but be a dog at cold starts. Idle also needs to have the right CO2 mixture, so set up your timing then take it to a mechanic for idle adjust if you don't have a co2 analyser.
Good luck
Leadfoot
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1981 ROW 924 Turbo -
carbon fiber GT mish mash
LS1 conversion in progress...

[Slam]

Yes, I will adjust timing. I'm kind of the 'twist and listen' school for that - there's definitely a sweet spot. If I miss, I'll go to 8 degrees BTDC as posted here by Ozzie. All emissions are off the car.

Well, I put the vac back where it belongs. Still bogging.

Does the switch on the mixture control unit just turn on the fuel pump? Haynes says very little about this - could it also have a function at WOT?

My guess is that the problem's fuel related. Throttle is simply air. There's spark aplenty (advance may be out - I'll check) because once the car is up to highway speed there's no problem maintaining it. In fact, I seem to have found a little more top end power. I've also noticed the car bogs dramatically when shifting - right after the shift, actually. It's a white automatic. !-)
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'88 944 Auto - may or may not resurrect

[leadfoot]

As I said, you can have a lean mixture low advance and still run at speed, but it will take forever to get there.
Idle is ; air + fuel + advance... a high idle bypass will counter low advance but run like crap off idle.
So set timing first as this is easiest and gives a benchmark for the other settings. If you have a vaccum gauge this with make things easier too, as you can usually read off around 18" at idle on a good stock motor at 950rpm, on your auto you should have about another +50rpm to play with the aircon/lights engaged...
Leadfoot
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1981 ROW 924 Turbo -
carbon fiber GT mish mash
LS1 conversion in progress...

[Slam]

Thanks, Leadfoot. I'll fix the timing tomorrow. Makes sense if it's the benchmark. Didn't realize that - guess I'm used to the 944 thinking for me.

If timing was set by PO to compensate for vac leaks/faulty AAV then this should do it.

I'll let you know how it turns out.
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'88 944 Auto - may or may not resurrect

[Lizard]

best to use a timing light and set it to 6 BTDC at idle.
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3 928s,

[924RACR]

As Lizard said. I'd be suspicious of timing and mixture.
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Vaughan Scott
Webmeister
'79 924 #77 SCCA H Prod racecar
'82 931 Plat. Silver
#25 Hidari Firefly P2 sports prototype

[Eturbo924]

My car was doing the same thing until I remembered that I had disconnected the fuel metering plug. I had done this to shut off the noise so I could determine if the fuel pump was pumping. There was so much noise from the metering unit that I could not hear anything else. So... my pump was dead.

Anyway... put a good used pump in... found a bunch of vac leaks... and fixed them. Then I could not figure out what the heck was wrong... why it was just bogging as soon as I got on the throttle. Du.... felt like a dope when I figured out what I had done. Put the plug back in and bingo car runs great! Now not only does she look real sweet but she runs great. Will be even better once I get a replacement AAV. Yeah that is bad so when cold she is not great but once warm! Weee!

This is the 1980 that I am fixing up. She is no longer a bees nest filled with leaves but a bright beautiful red sports car again!

Eric
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1982 924
1992 968
2003 C4S
Parts Parts Parts and More parts.
E-mail me for parts you need!
Drive Fast!

[Slam]

Gotcha. Fuel metering plug - is this the rubber plug over the 3mm mixture adjuster? I'm guessing it is.

Fuel pump is good - jumpered it and it's not noisy. Very smooth, in fact.

Okay - the story so far. I adjusted the timing - managed to advance it quite a bit before finding the sweet spot. Car runs better from standing start - no bog there. Car still bogs just after shifting and runs rough. Will check cap, wires and plugs as well.

Now, as I understand it, a richer mixture will allow me to run more advance, yes? By fixing the AAV and doing the work I've done, I've eliminated (hopefully) any false air and thus the mixture is richer. Hence, more advance. Before I adjust the mixture (which I'd rather not mess with yet), what other things can I check? I'm not suspecting the WUR because the car'll run the same warm and cold. There are no hot-start or cold-start problems.
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'88 944 Auto - may or may not resurrect

[Slam]

Well, thanks, everybody. Problem was timing. So I drove and tweaked until I sorted it. Car has more power, shifts smoother and at higher RPM, so top end has improved. Was missing plug on fuel distributor, too.

Cheers, lads.
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'88 944 Auto - may or may not resurrect