944 Starts Hard, Hunts, Stalls & Dies...

Porsche37 · 06-06-2011, 10:01 AM

Well, why all you fully running Porsche owners soak up the sun driving the back roads of where I would like to be, I have a 86' N/A 944 that just won't start...

OK, she barely starts with a lot of gas and if I keep the RPM's up above 1200 she runs rough, and the exhaust makes a odd noise I never heard prior. If any good ideas as the area of concern, some background...

Just started her last month for the first time, final part replaced was a fuel pump, after one year of part replacement/maintenance, and she ran fine, revved above normal but if I touched the gas pedal she dropped down to 800-900 rpm and ran all day long, straight and true. Great fuel pressure, everything was fine.
She was fixed, so I thought...

Well, last week after replacing a few not related minor dash parts, still in the shop, I tried to start her, but nothing but a lot of gas would get her up and then she would stall. So I replaced the DME relay, no change.

Things that are brand new out of the box to Porsche standard:
1. Coil, plugs, wires, disrt, battery, ICV, and starter
2. Fuel pump, fuel filter, fuel reg, fuel damper and flushed gas tank
3. vacuum lines, all checked and rechecked
4. dme relay, dme temp sensor
5. water pump, timing belt

All engine grounds were redone, wire brushed to shiny metal, since I pulled the engine for a cracked oil cooler housing and clutch replacement, etc...

Checked the MAF, internals too, resealed and attached (visual only).

Checked the Motronic at a electrical shop, all looks clean inside and out.

Checked plugs, all are firing, but sounds like the timing is off when she can run, no wet fuel.

All was working great, then kaput...

Has to be something simple I missed, where or what???

CatsEyes · 06-07-2011, 05:41 AM

Crank angle sensor or speed sensor, possibly? Don't see those in your list.

(Plus a bump so the real experts can help...)

Porsche37 · 06-07-2011, 11:26 AM

Checking sensors now. Just ordered an updated bracket to check the problem. I will have a brand new 944 in a few months if this keeps going on! Thanks...

RedBaron · 06-09-2011, 09:06 AM

If you think it's the sensor and you are considering purchasing a new one, somebody found out on rennlist that the same sensor is used for the E30 BMW generation and the numbers are cross referenced. I believe it is a lot cheaper (only difference is the wire is a bit longer.)

TibetanT · TibetanT's Garage

Hello There:

I was wondering when the last time the belts were changed, checked and tensioned. Specifically, are you sure the timing marks are lined up?

Next question: does the tachometer bounce/move when you crank the engine over with the key in start position?

If tachometer doesn't move then you may have issues with speed and reference sensors. Or, maybe the connections for these are loose.

One test, try spraying starter fluid into the AFM housing, reseal and try starting. Does the engine run for a minute?

How are fuses and relays in fuse box?

Hope some of this helps and, good luck.

TibetanT · TibetanT's Garage

Okay, noticed that you did the timing belt.

When you worked on the wiring behind the dash, did you by some chance unplug the starter switch? Maybe some wiring is not completely connected. Just a thought, since it is always the little stuff that come back to haunt us at times.

Porsche37 · 06-10-2011, 10:51 AM

Already bought a set earlier, thanks for the tip R.B. I planned ahead, but forgot the new clamp for them, darn! Nice wheels. What are running front and back?
The belts were done right before I bought her T.T. I am wondering if it's worth the check once again. I'm inclined to the sensors as I see no tach bounce. Engine stays running if I feather the gas pedal. Soon as I take it off, it shuts down faster than a bank at 3 pm friday afternoon.
Checking the fuses again, easy is good by me, but to avoid frustration I started fixin the lowdown drivers side electric window...

Guest765 · 06-10-2011, 10:55 AM

Quote:

Originally Posted by Porsche37

Already bought a set earlier, thanks for the tip R.B. I planned ahead, but forgot the new clamp for them, darn! Nice wheels. What are running front and back?
The belts were done right before I bought her T.T. I am wondering if it's worth the check once again. I'm inclined to the sensors as I see no tach bounce. Engine stays running if I feather the gas pedal. Soon as I take it off, it shuts down faster than a bank at 3 pm friday afternoon.
Checking the fuses again, easy is good by me, but to avoid frustration I started fixin the lowdown drivers side electric window...

Fuses and crank sensors would not fail in this manner there is no "kinda works " failure mode with them really.

CatsEyes · 06-11-2011, 01:13 AM

Quote:

Originally Posted by fwayfarer

Fuses and crank sensors would not fail in this manner there is no "kinda works " failure mode with them really.

Actually, my crank angle sensor 'kind of worked' for about two years, it seems. Previous owner had mysterious intermittent problem; went away; returned on me one day with a vengeance. Easy diagnosis with help from the good folks here.

So yes, still do check the sensors. The tacho non-bounce does maybe suggest them.

Porsche37 · 06-19-2011, 12:14 PM

Final answer to the BIG mystery... Vacuum leak! Yes, replaced all lines EXCEPT for the one behind the air box. The short 3" connection to the venturi valve cracked open. I pulled the box in frustration and was intending on finding the problem. What a relief! Thank God there it was... Back up and on the road. Idles high, but thanks for all the help...

guru944 · guru944's Garage

Porsche37;

Sounds strange!
I would check the Ignition Timing & see what it is set to?

Then vacuume readings.....
Later

Porsche37 · 06-20-2011, 03:53 AM

I am narrowing in on the TPS, plus I have a slight topside wiggle in the butterfly valve... Need to install a rebuild kit I have for the TB that I bought that is sitting in my box of goodies.