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WHAT is wrong with this car?!? (Now w/ video)



Look familiar? Yep, this JUST happened to me 2 weeks ago. I'm starting to reach my boiling point with this supposedly "well maintained" vehicle. I'm seriously considering selling it and just starting over with another one with less issues... At the moment however, I want to sort out what the issues could be - that way I can sort out if it's worth my time, money, and effort to fix them.

I'm having 2 issues that have combined themselves in a particularly nasty way to make the car a ticking time-bomb of random failure... The biggest problem is the HUGELY fluctuating idle whenever the car is cold - it wanders steadily and rythmically between 100 and 1200 rpms, and will not stop wandering until it's been driven for a few minutes. The fluctuation is so great that it actually often stalls itself out, which is where problem #2 kicks in: The battery seems to be so bad, that it can only hold enough charge for one round of cranking (which can be a good 30 seconds or more, mind you). So after I've struggled to get the car started once, it then idle-fluctuates itself to death and won't turn over again, leaving you dead wherever the car stalled itself out.

I'm hoping the no-restart issue is just a bad battery, but I thought I'd just double check before I go spend $100 on a new one. As far as the idle and starting problems, I was told vacuum leak a while back, but it just seems way to much of a variation and way to rhythmic for a vac. leak

To recap:

> Hard-starting: Cranking for 10-30+ seconds, while giving significant throttle.
> HUGE idle fluctuations until driven (with engine warm or cold), often stalling the car out.
> Something amiss with battery / charging system.

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1985 Porsche 944 - '85/1 N/A, currently for sale.
1971 Datsun 240Z - Street / AutoX car.
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Last edited by Z06C5R; 06-07-2008 at 09:53 AM..
Old 06-06-2008, 03:33 PM
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You might just have poor electrical grounding, maybe even loose cable...
A connection may be making and breaking with vibration.

I would try to sort out the battery/charging first, then the starting issue.
In fixing one issue, you may well find out what is causing the other(s).


best of luck.

Russell
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Old 06-06-2008, 04:32 PM
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Yeah, if there are bad electrical connections and the DME isn't getting enough juice, who knows what that would cause. What voltage do you get at the battery when the idle is bad. Does the charging light come on indicating that the alternator isn't working? Does that battery crap out even if it's been fully recharged with a bench charger? If it does, the battery could be bad.
Has this been going on for awhile, or did it just pop up recently?

Check the battery clamps. If they are not the crimped type, the contact between the wire and the clamp could be corroded. The cables themselves sometimes corrode inside and deteriorate without any outward indication, so look for any internal corrosion under the insulation on the ends. That goes for the alternator wire as well. Also check for corrosion at the positive lug at the starter where the alternator wire and the main battery wire are bolted. This is the only way for the alternator voltage to get to the battery. Also check the main chassis ground near the battery and also the engine ground bolted to a stud on the top of the bellhousing behind the cylinder head. And, of course the DME ground, but I don't know where that is. I'm sure someone else would be able to say.

Beyond that, it could be a big vacuum leak. The large rubber hoses under the intake manifold in particular deteriorate after a while. It could be a dirty or bad idle stablizer. The idle circuit inside the throttle body could be clogged up with gunk, forcing the idle stabliser to try to compensate and end up fluctuating.
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Old 06-06-2008, 04:54 PM
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The battery cables and grounds all look good, at least outwardly. The battery light only comes on right at the very bottom of the fluctuation, where the engine is more or less temporarily dead. I'll double-check the wires tomorrow when it's light again, but I'm fairly certain it's a bad battery - just a few minutes of playing music w/ the car off is enough to drain it.

In terms of the idle... The more I think about it, the more I think it's something to do with the computer / sensors. It's to perfectly rhythmic and consistent to be a vac leak IMO. If you watch the MPG gauge inside the car, you can see it fluctuating with the idle, like the comp is giving the engine more throttle to keep itself from dying (which is exactly what it sounds like). I'll see if I can get a video of it tomorrow.
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Old 06-06-2008, 06:17 PM
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Could be the computer dealing with a vacuum leak. I know it's not a 944 but my toyota 22re was doing this same thing. Very rhythmic, from almost dead to over a 1k. I went crazy trying to find it - all sensors tested good, computer good, replaced all gaskets on the top end. Turned out to be the head gasket, as I discovered when I found chocolate milk one day. Did the head job and all was well.

Could be anything really...a good cheap first step is to go through every electrical connection you can get to and clean it up, whether or not it looks good. I use a baking soda/water mixture on any corrosion, like the + battery connection, and that seems to work well.
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Last edited by andykrow; 06-06-2008 at 06:34 PM..
Old 06-06-2008, 06:24 PM
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I had 2 years of problems with my 83 944 before I was able to get it to be a reliable driver. I now have had the car for over 6 years and like the 944 so much I just bought a 951S.
Old 06-06-2008, 06:37 PM
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Dumb question....How old is the battery??? Ever get the alternator checked?

Idle issue definatly sounds like a vac. leak. Common to happen.

Could definatly still be a ground issue. The cables corrode. You wouldn't see it on the outside. Checking the resistance of the cable is the only way to really tell.
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Old 06-06-2008, 06:45 PM
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Quote:
Originally Posted by Z06C5R View Post
The battery cables and grounds all look good, at least outwardly. The battery light only comes on right at the very bottom of the fluctuation, where the engine is more or less temporarily dead. I'll double-check the wires tomorrow when it's light again, but I'm fairly certain it's a bad battery - just a few minutes of playing music w/ the car off is enough to drain it.

In terms of the idle... The more I think about it, the more I think it's something to do with the computer / sensors. It's to perfectly rhythmic and consistent to be a vac leak IMO. If you watch the MPG gauge inside the car, you can see it fluctuating with the idle, like the comp is giving the engine more throttle to keep itself from dying (which is exactly what it sounds like). I'll see if I can get a video of it tomorrow.
If the battery is that bad, I would definitely say replace it. No use troubleshooting electrically controlled problems with a screwy battery. Check the voltage at the battery while it's running just to be sure that it's not seriously low. The engine controls will probably wack out if they aren't getting juice. I've heard you do not run these cars with no battery installed, or something bad will happen (Idon't know what, though). It could be bad enough to kind of seem like almost having no battery, which could be screwing with the DME voltage somehow.
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Old 06-06-2008, 09:13 PM
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I'm sure this isn't your no-start problem, but maybe it's part of your other problems, and i'm going to try it with mine. I'm going to change my water temp DME sensor, if your terminals/wires are corroded it can cause more resistance than it should and the DME reads this signal and adjust the fuel totally wrong. THis would also contribute to poor idle on warmup and also contribute to overall poor performance. And it's only 7 bucks for the late model sensor.
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Old 06-07-2008, 07:10 AM
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I would address the battery issue first. A stalling car sucks but its even worse if you cant get it restarted because of a bad battery. You can get the battery tested but if its old it might just be time anyway.
Old 06-07-2008, 08:17 AM
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Just checked the voltage while the car was running (poorly)... 13.73v grounded to the engine or the negative battery terminal - that doesn't seem like a dead battery to me. Strangely enough though, not minutes before taking that reading, I had to pop-start the damn thing because the first time the car started it stalled itself out, and then wouldn't turn over again. HOWEVER, I'm starting to think maybe it's flooding itself, and perhaps that's why it won't crank? I'll typically spend about 30 seconds cranking it before it fires, and when it does eventually fire it usually blows a lot of gas-smelling grey-ish smoke and runs incredibly rough for a few seconds.

In other news: Here's a video of the idle wander, with a shot of the tach and mpg gauge to give you an idea of what's going on: Pay close attention to the MPG gauge... I think that might be a good hint at some kind of comp-related issue.

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Last edited by Z06C5R; 06-07-2008 at 10:03 AM..
Old 06-07-2008, 09:29 AM
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Vacuum leak!

And if it starts when you jump it or pop start it, I would really replace the battery.
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Old 06-07-2008, 11:40 AM
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[QUOTE=Z06C5R;3989175]Just checked the voltage while the car was running (poorly)... 13.73v [QUOTE]

This only means your alternator/regulator is trying to do the right thing.

Take it to a auto battery shop. They can load test it for you while it's still in the car.

Sounds like vacuum to me also.

Jeff
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Old 06-07-2008, 12:45 PM
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The battery was 12.26v with the car off yesterday, IDK if that means anything to anyone, but I thought I'd throw it out there anyhow.

So if it's a vac. leak, the computer must be trying to correct for it somehow - it's way more rhythmic than and vacuum leak I've ever seen, and the coordination of the mpg meter with the rev-waves is suspicious to me.
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Old 06-07-2008, 03:36 PM
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I'd say the battery is at about 50% capacity.

Here's a site for reference (there's many more out there)

http://www.megapulse.us/FAB/technical.php

Jeff
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Old 06-07-2008, 10:17 PM
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Doesnt the MPG gauge on these cars work off of vacuum?? I don't think its DME controled at all. That deff looks like a vac problem, The DME is screwing with the idle stablizer trying to get the engine to stay running, It will open and close the valve, Open when idle is too low, CLose when too high, Thats why its rhythmic like that cuz its just going back and forth trying too stay alive. I would first, Throw in a new battery, Check for a draw on the battery too. Then check and clean grounds and other connections, NExt I would start checking ALL vac lines, Then I would check Fuel reg and Damper to make sure they arent leaking fuel or vac.
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Old 06-08-2008, 09:52 AM
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Why in the f*ck would you put that ghetto-ass "black-out" crap on your taillights?

Sorry for the hijack, but if there's one thing I've learned about 944s it's that they're dangerously succeptable to being rear-ended by inattentive idiots following them. Our cars are low and the taillights are well below the typical line of sight of the average rolling road behemoth out there with Suzy Soccermom at the helm. This is an even bigger problem on the early cars, since they don't come with a 3rd brake light as the later cars do (I put one on mine for this reason).

As a general rule, ANYTHING you can do to make yourself more visible is smart. Anything that makes you less visible is frankly pretty damn stupid. Are you deliberately TRYING to get rear-ended?

A rear-end collision in a 944 that tweaks the rear panel, either of the two rear quarters or breaks the hatch glass is a guaranteed total loss. Your car, you decide but when I looked at that photo, it's the first thing that jumped out at me. Plus it looks childish/ricey, but that's just me. . .

Best of luck sorting the car out. Just keep in mind what a shame it would be if after putting all that time into it, you got rear-ended five minutes after rolling it out of the garage.

Leave the Pep Boys pseudo-bling stuff to the Honda crowd, k?
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Old 06-08-2008, 11:51 AM
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...Suzy Soccermom at the helm...
Ahhh! White Suburban; 90 pounds; long blonde hair; cell phone stuck to the side of her head (right next to the nipple labeled "inflate to 50 PSI")...

She is responsible for the dent on my front quarter...left the scene...couldn't get the plate number...blocked by a semi...

I didn't know she lived in your neighborhood?!?!?
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Old 06-08-2008, 12:09 PM
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I am gonna go with "Vacuum Leak" as well. If I were you, I would purchase the silicone vacuum line kit from Lindsey Racing... one of the best $35 investments you will ever make. The replacement should take you about 10 mins, max
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Old 06-08-2008, 01:17 PM
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The last time I looked at the back of the instrument cluster I don't remember seeing a vac hose to the tach dial. The workshop manual states the following;

Economy Control

The economy control displays the
instantaneous fuel consumption in ltr/
100 km (miles per gallon) or ltr/hour
(gallons per hour) depending on road
speed and injector time (ti = signal of
fuel injectors).

and goes on to state;

Signals Required for Operation

Economy Control - Road speed (hall sensor
signal) from speedo-
meter
- Injection signal
(ti signal) from DME
control unit.

Sure enough, looking at the schematic, the road speed signal is also connected to the tach, and the same dial (assume to be the economy dial) on the schematic has a connection to pin 11 on the DME.

The other dial on the tach also goes to pin 1 on the DME. This is also the coil signal so it's safe to call this the tach signal.

There's still a chance that the fault is the DME.

Jeff

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Old 06-08-2008, 11:36 PM
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