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I'm About to Set This ****ing Car on Fire!!!!!

My 1988 944 NA will not run for more that 10 seconds. With the DME coolant temperature sensor unplugged it will run, but it idles at 1800 RPM. It runs beautifully at that RPM, then it starts to cough and dies. If I gently open the throttle it will continue to run, but if I go over 2500-3000 RPM it starts to misfire and is generally not happy.

Here are the things I've replaced recently. Most of them are because they were 25 years old, not because I was trying to solve this problem. I have replaced the fuel filter, fuel pressure regulator/damper (no gas smell when the vacuum lines are removed), fuel injectors were rebuilt, fuel lines, spark plugs, cap, rotor, wires, every vacuum line (including the large one from the J boot to the AOS , the ones from the J boot to the ISV/intake manifold, and the one from the brake booster to the J boot), ISV, AOS seals, intake manifold gaskets, J boot, all grounds are clean, DME coolant temperature sensor, TPS, DME relay, and my throttle body was resealed/cleaned.

The idle adjuster screw in the throttle body is not backed out/missing. All vacuum connections are tight/correct. My tachometer bounces like it's at a rave. My TPS is adjusted correctly. The O ring at the back of the throttle body is there. My J boot is on tight. The wires for the AFM and DME coolant temperature sensor look immaculate. I recently installed the Rouge Tuning NA-Tune and I have verified that my MAF sensor is working correctly. I have tried smacking my DME and there was no change. The legs on the chip are not bent/missing. The spark plug wires are hooked up correctly. My battery is fully charged. My car has no oxygen sensor at the moment, but that shouldn't really matter, right? I do not have the old AFM, so I can't swap it back in, but I'll try finding and el cheapo one just to troubleshoot with.

I'm sure you guys are going to tell me to search, but all of the threads I've come across are no help, or the OP never posted back saying that they fixed the problem.

Please help! I have no form of transportation at the moment, so I need this piece of **** running!

Old 02-05-2013, 01:39 PM
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How doe the DME look inside
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Old 02-05-2013, 01:50 PM
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Can you swap out your DME with a known good one?
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Old 02-05-2013, 01:50 PM
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The DME is bone dry on the inside. I was fortunate enough to not have my battery box rust through.

I don't have any spare DME's to test with at the moment. Before I drop $300 on a DME, I might send it away to be tested.
Old 02-05-2013, 02:05 PM
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I'm not an expert withe the temp sensor but if it was me once it is running with it disconnected and the engine is warm I would plug it back in. If this works the sensor is FUBAR and perminently indicating that the engine is hot.
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Old 02-05-2013, 02:46 PM
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When you unplug it the mixture will get richer but too rich for the engine to run well when it is hot. Pluging it back in will short the wires and return the mixture to normal.
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Old 02-05-2013, 02:50 PM
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Quote:
Originally Posted by Tom944 View Post
I'm not an expert withe the temp sensor but if it was me once it is running with it disconnected and the engine is warm I would plug it back in. If this works the sensor is FUBAR and perminently indicating that the engine is hot.
What does FUBAR mean?
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Originally Posted by Tom944 View Post
When you unplug it the mixture will get richer but too rich for the engine to run well when it is hot. Pluging it back in will short the wires and return the mixture to normal.
I was told I can stick in a resistor in the coolant temperature sensor connector to tell the DME that the engine is warm and lean out the mixture. I tried 47 a ohm resistor and the engine wouldn't start. Do I need a 47K ohm resistor instead of a 47 ohm?
Old 02-05-2013, 03:21 PM
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According to Clark's it's Between 3k3 and 1k5 cold and is about 300 ohms hot.

FUBAR -F'ed Up Beyond All Recognition!!!!
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Old 02-05-2013, 03:53 PM
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The dme temp sensor can cause all sorts of running issues if it's on it's way out or dead.....
I'm sure you checked but is the engine grounded? clip a jumper cable from the block to the batt neg for a quick check......
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Old 02-05-2013, 04:39 PM
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Quote:
Originally Posted by Tom944 View Post
According to Clark's it's Between 3k3 and 1k5 cold and is about 300 ohms hot.

FUBAR -F'ed Up Beyond All Recognition!!!!
The sensor is brand new from Pelican, so I hope it's not FUBAR'd.
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Originally Posted by bell View Post
The dme temp sensor can cause all sorts of running issues if it's on it's way out or dead.....
I'm sure you checked but is the engine grounded? clip a jumper cable from the block to the batt neg for a quick check......
I'll try that. There was one ground I couldn't reach on the back of the bell housing (the one closest to the firewall), so maybe that's what's screwing me over?

Edit- No change with the jumper wire.

Last edited by Chunkerz; 02-05-2013 at 05:05 PM..
Old 02-05-2013, 04:55 PM
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I have had new dme relays fail.....mainly due to the fuel pump pulling to much current, is the relay getting very hot?
When the car stalls is the fuel pump running? The car will run for about 5 seconds after the pump shuts off.....meaning if the dme relay is failing it can cause just the pump to lose power.

But I think there is something going on with the temp sensor.....check it's resistance at the sensor with it unplugged, then check the resistance at the dme (with sensor plugged in and dme unplugged) it should read the same, if not it could be a ground issue......

Do as mentioned, with it unplugged let it idle up to warm then plug it in...and see if it gets better.....

I know for a fact when the engine is cold and the sensor is unplugged it will run exactly as you describe....
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Old 02-05-2013, 05:53 PM
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Don't give up. I have wanted to set my car on fire MANY times. Sometime I wish the fuel line would brake while I'm drive to collect the insurance money. But when the car is running right, they are a blast and you will be glad that you didn't light it on fire. No real help here, but good luck.
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Old 02-05-2013, 06:13 PM
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Sometimes I hated my car so bad I wanted to watch Kyle set it on fire for me!
Old 02-05-2013, 06:41 PM
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Quote:
Originally Posted by bell View Post
I have had new dme relays fail.....mainly due to the fuel pump pulling to much current, is the relay getting very hot?
When the car stalls is the fuel pump running? The car will run for about 5 seconds after the pump shuts off.....meaning if the dme relay is failing it can cause just the pump to lose power.

But I think there is something going on with the temp sensor.....check it's resistance at the sensor with it unplugged, then check the resistance at the dme (with sensor plugged in and dme unplugged) it should read the same, if not it could be a ground issue......

Do as mentioned, with it unplugged let it idle up to warm then plug it in...and see if it gets better.....

I know for a fact when the engine is cold and the sensor is unplugged it will run exactly as you describe....
I'll test the resistance and report back. I can't start the car again until tomorrow since it's almost 11 and my car is loud as crap with no O2 sensor and rice can the PO put on.

Edit- The reading at the sensor was 4.75k ohms. At the DME it was 4.76k ohms. I had to go inside for a few minutes to find a labeled picture of the DME connector/grab a jacket, so the temperature may have dropped in the 10 or 15 minutes I was inside
Quote:
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Don't give up. I have wanted to set my car on fire MANY times. Sometime I wish the fuel line would brake while I'm drive to collect the insurance money. But when the car is running right, they are a blast and you will be glad that you didn't light it on fire. No real help here, but good luck.
I've never had the car safe enough to drive more than around the block (brakes are FUBAR'd from the PO racing it), so I've never really had the chance to enjoy the 944 experience Once the brakes are finished (working on it right now) and I get this solved then maybe I'll get to enjoy my car...

Last edited by Chunkerz; 02-05-2013 at 07:02 PM..
Old 02-05-2013, 06:45 PM
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My cooling system bleed screw just snapped the head off. Set it on fire!!!
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Old 02-05-2013, 07:23 PM
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That sucks Gawernator. At least that screw is easy to get to.

I just took off the shift linkage on my white car for the first time. The PO had broke the head off of one of the bolts, and since it was tight, they just left it. So I had to drill it out. That sucked.

Now I have a short in the reverse light that keeps blowing fuses. Set it on fire, YES.
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Old 02-05-2013, 07:52 PM
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Lets have a bonfire and burn our cars!
Old 02-05-2013, 08:23 PM
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Quote:
Originally Posted by GreenWater View Post
That sucks Gawernator. At least that screw is easy to get to.

I just took off the shift linkage on my white car for the first time. The PO had broke the head off of one of the bolts, and since it was tight, they just left it. So I had to drill it out. That sucked.

Now I have a short in the reverse light that keeps blowing fuses. Set it on fire, YES.
I saved the day with a bolt from Home Depot... finished the coolant bleeding and car seems to be driving great! I have to tell you though... got stranded for ten minutes when the shift lever bolt came apart from the kit.. I'm gonna take the blame on this though. i tightened it up more than before and the shifting is better than I ever dreamed, even the first time. Maybe I was scared of over-tightening idk. But I should have noticed the shifting was getting sloppy.

Also yeah, I bought an extractor kit for $8 but went with my gut and it turned out easily with jeweler's pliers.
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Last edited by Gawernator; 02-05-2013 at 10:08 PM..
Old 02-05-2013, 09:59 PM
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OP problems sound like a vacuum leak. Recheck all hoses including ICV to intake manifold and venturi to intake manifold. Make sure intake manifold gaskets are in place correctly and that intake manifold has been torqued properly to head.
Old 02-06-2013, 04:18 AM
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I've checked and and rechecked the vacuum lines many times. The intake gaskets were replaced when I changed my vacuum lines and all 8 bolts are torqued down to 20nm.

Someone suggested that I check the speed sensor because it may be flaking out and sending funky signals to the DME so the DME thinks the engine is stopped and cuts fuel.

Old 02-06-2013, 06:23 AM
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