Trouble starting/rough running

akron · akron's Garage

My 1983 NA 944 was running great and suddenly has trouble starting. Once it starts, it runs rough and blows black smoke. If I pull the fuel pump fuse, it starts and runs normally and smoothly for about 30 seconds until the fuel is used. I have had this problem before and swapped a fuel pressure regulator from another 944 and it started and ran okay. I reinstalled the original pressure regulator and it ran fine too and has until now and the problem is back. Do fuel pressure regulators stick? Am I on the right track? Any ideas? If I get a chance this weekend, I will check the fuel pressure and post it.

Cocacolakidd · Cocacolakidd's Garage

Sounds like you are running very rich all of a sudden - could be a sticking/faulty fuel pressure regulator - could also be a couple of other things making the motor do this. The idle air regulator is a culprit often enough, along with the DME temp sensor. Check and see what the pressure at the rail is first, and go from there.

ZR8ED · 05-25-2012, 04:45 AM

Put a guage/tester on the fuel rail. I had a similar issue. Car would start right up for a few seconds, then die out. I checked the fuel pressure, and it was fine for a few seconds, then would spike to 100psi, and car would stall. In the days leading up to it, It had some hard starting/stalling. I installed a new fpr, and all was well.

akron · akron's Garage

Okay, slow going. House is painted and reroofed and, well the fuel pressure on the rail was 35-36 steady. I have another 944 that I will compare pressure with as soon as I get the lawn cut and the battery charged. If the pressure is less, I'll swap FPR's and see what the result is. I'll post results as soon as I can get TIME TO PLAY with my toys. I'm thinking you guys have pinned it down.

akron · akron's Garage

Checked my other car. It's fuel pressure on the rail is 30. Thinking fuel pressure regulator? Thought I might swap them, but maybe I'll just buy a new one and install instead of double the work! Thoughts?

Ky914Newbie · 06-05-2012, 04:44 AM

+1 on the FPR. But I would pull your spark plugs and see what they look like. I am in the process of fixing a rough running issue on my 951 and it turns out I was only running on 2 cylinders. I replaced the Distributor cap/rotor and plug wires because they needed it anyway and no improvement. I think my issue is the injectors are clogged. I just sent them out to witchhunter. 2 of my plugs showed really rich and 2 looked like they hadn't ever fired.

akron · akron's Garage

Swapped spare FPR in and have the same symptoms. I let the car warm up though, and the idle smoothes out once the temp comes up and the car then runs fine. I had checked the idle air regulator operation a little while back and it was pretty solid. I will hunt down the DME temp sensor and check that bad boy and post results. Thanks!

Cocacolakidd · Cocacolakidd's Garage

The DME Temp Sensor is under the J-Boot - in the head front part of motor. There are two temp sensors there close together, one is the sending unit for the temp gauge in the dash cluster, the other is the temp sensor for the DME.

akron · akron's Garage

Checked the DME temperature sensor and it read around 2.1K ohms which is in line with having had the engine running a while before, so the engine was not stone cold. I tried the same measurement on my other car and it was above 3K ohms; it was cold. Had to drop the progress and go to work.

I had tried this reading at the sensor and not at the DME. Being an electronic tech, I knew that I had to check at the DME to see if the reading was correct at the DME too. When I got home from work, I checked at the DME and it was the same and seemed right. So, I figured I would start the engine and warm it up and check the reading. Well, it started up and ran perfect!

I think that when I pulled the connector and reseated it on the temperature sensor, it cleared the problem. The connector is a bit loose compared to my other car. I will rework the connector with a new one and hopefully keep that problem at bay!

I am lit up...summertime in Alaska is way short and I gotta get as much of this car in as I can while the snow is not here! Thanks for the help guys! I will post more to this thread if it develops further.