Interesting Engine Cut Out Issue, Thoughts

[Dave Colangelo]

So I DD my 944, 22 miles to work every morning sometimes in a lot of traffic. I have been doing this for about a month now without any issues. Before that I was in college but drove the car at least every other day. Never super far but always without any issue. The car has run flawlessly for the past year that I have had it, I gave it regular oil changes, some other minor things were tended to but overall not much was touched. The car is completly stock with the exception of a PowerProm chip. Now to the issue, it all began this past weekend,

I was out on the shore for the 4th and I drove the car out there and parked it for the weekend. I got in it on sunday to leave and the engine turned over, caught for a second then died. I tried to restart it as this happens ever once in a while if there is not enough pressure in the fuel system. No Start. Tried for the next 10 minutes, no start. At this point I was getting scared something had gone wrong. Tried my spare DME relay, nothing. Jumped the fuel pump to make sure it was working and felt pressure in the lines as well as heard it pumping so that was not the issue. Pulled a spark plug out to check for spark and did not see any. Got kinda freaked out at that so I let the car sit for 25 minutes. Got back in and it started right up. I figured I must have flooded the engine and due tothe extreme humidity it just took some time for it to clear out.

Anyway I drove the car home and had no problems on monday getting to work. But then yesterday morning, going down the highway, sudden loss of power and I realised the engine cut out. I rolled over to the side gathered my self and turned the key. The car started right up no problem. I thought little of it so I continued on to work. Then today on the way the engine cut out at almost the same point in the drive. Ignoring voodoo forces and strange EM fields I was a bit curious this time. Today it would not restart as it did yesterday. I swapped the DME out for my older spare and it started right up. The relay was also very warm and Im thinking may have been the issue. Anyway about 1 minute later I was driving down the road and the engine cut out again, this time I down shifted and was able to bump start the car with out a problem. I continued the 40 minute drive to work with out any issues. This all seems very strange to me and I dont know what to make of it. maybe I just need to let the car warm up? Could it be a hot start issue? Could it be a cold start issue? Is it nothing to worry about and im just freaking out? Could it have been the humidity (its been very humid here recently)?

Anyway I decided to take some countermeasures but I can't work on the car untill this weekend so I have ordered a
- New air filter (not sure how old the current one is and it may just be clogged)
- Fresh Spark Plugs
- Fresh plug wires
- Note the PO put these high performance wires on the car that I never much cared for as they seemed fragile but I never thought to replace them.
- I will be running a can of seafoam through the system to clear it out
- Oil change if I have the time
- Check distributor (sand if necessary)
- Making a proper DME jumper to keep in the car
Will also be ordering a new DME relay


Post your thoughts im interested to hear some suggestions

Regards
Dave

[Ky914Newbie]

Intermittent issues like this are never fun to diagnose.

I hope it is something small that you are already planning on fixing. It could also be the plug to the AFM coming loose. It concerns me you didn't see spark the one time you checked for it. Are you certain there wasn't any spark?

Other things to consider are the speed and reference sensors and the DME Computer. Have you had to jump start the car recently? Jump starting the car is hard on the computer.

[jpk]

I'd look at replacing the engine speed and reference sensors. These are key to getting a good spark at the right time. The sensors themselves don't necessarily wear out, but the wire and connectors degrade over time. If the connection is at all marginal, you could have problems. Lindsay has a replacement harness that runs from the DME to the sensor connections as well

If you've 100% eliminated those as a potential cause of the problem, you might consider having the DME itself overhauled.

[John_AZ]

Dave,

Porsche sent out a TSB with your exact problem-really!.

But I cannot find it...

jpk's & Ky's suggestion is the top of the list. Sensors not set correctly, frayed insulation, plastic connectors falling apart.

If your spare DME/Fuel pump relay was an old, used replacement, get a new Stribel in addition the the 3 wire you plan to make.

I would wait on the SeaFoam until you correct the current flaw or you may add more symptoms to the problem.

GL
J_AZ

[Dave Colangelo]

The seafoam is just to clean everything out, I feel as though at this point it cant hurt. New DME relays are on the way as well. I checked the sensors when I had the first issue and the wires seemed to be in good shape and connected. Maybe some dielectric grease on the connectors will help. I know they are an expensive piece so that may be a last fix. I have an oscilloscope so maybe I will just check their output.

new Stribel DME relay is on the list of things to order.

Regards
Dave

[Gawernator]

I agree with John_AZ's thesis but why would Seafoam have any negative effects? (Used correctly)

[AKCJ]

I had a very similar problem on a different car but it used the same bosch afm. The fix involved working on the afm. That was before I knew about adjusting the sweep to get to a fresh track but I assume that's what the mechanic did.

It was an intermittent cut out - I could drive for 1 minute or 1 week, then it would just shut off. Sometimes it would not start. Just like your symptoms.

I don't get how the afm could cause these symptoms. I would think as the arm hit a bad spot as it was sweeping, the engine would momentarily sputter? Not just stop all together. And how would bad spots on the resister plate cause the car to not start at all? Again, it doesn't make sense to me, but I guess it's worth looking in to.

[Dave Colangelo]

Interesting,

well the problem persisted on the way home today. Was in the car for 2 minutes, merging on to the road and boom nothing. Then it would not start right back up as it had before. I swapped in my other DME relay and the car started right back up and ran fine all the way home. So this is what I think.

Either my car has a 2 minute driving omen.

The DME relay is over heating and something is happening.

Somewhere in the warm up curve there is an issue and it cuts out at the same temp every time

There is a problem with my temp sensor somehow

I will be ordering 2 new DME relays and replacing them. I think I will also put a small heat sink on the side of one to see what affect it may have. I will also clean up the AFM with some contact cleaner.

Regards
Dave

[Dave Colangelo]

So it was the DME relay...

Today on the way to work it cut out again about 5 minutes into the drive. Got out swapped relays and went on my way. 30 seconds later it cut out again. At this point I realised my worst fear I not only 1 but 2 intermittent DME relays. I fashioned a very dirty jumper with some wire I found around the car. Got it in and got the car started. At this point I needed a relay so I went to the only place I figured may have one in stock, the dealership. I pulled in right as they were opening and went to the parts department. I asked what the chances were thaty they had a DME relay for a 944 the parts guy kindly responded with "slim to none but ill check". Luckily the 933 uses the same relay so they happened to have one in stock. Any one want to guess what it cost me...

98.76

Yup, 4 times what it would have cost me here but I needed it as I rely on this car every day and had to get to work. Reluctantly I bought it and low and behold the car started and ran issue free all the way to work. It was a stressful morning but a least I know I can run more or less problem free for the time being. I have 2 more on order and will keep them in the car as spares.

Regards
Dave

[AKCJ]

Glad you got it sorted out.

I've only had the DME relay fail once and it was on the way to work.

[John_AZ]

Originally Posted by Dave Colangelo

So it was the DME relay...

Today on the way to work it cut out again about 5 minutes into the drive. Got out swapped relays and went on my way. 30 seconds later it cut out again. At this point I realised my worst fear I not only 1 but 2 intermittent DME relays. I fashioned a very dirty jumper with some wire I found around the car. Got it in and got the car started. At this point I needed a relay so I went to the only place I figured may have one in stock, the dealership. I pulled in right as they were opening and went to the parts department. I asked what the chances were thaty they had a DME relay for a 944 the parts guy kindly responded with "slim to none but ill check". Luckily the 933 uses the same relay so they happened to have one in stock. Any one want to guess what it cost me...

98.76

Yup, 4 times what it would have cost me here but I needed it as I rely on this car every day and had to get to work. Reluctantly I bought it and low and behold the car started and ran issue free all the way to work. It was a stressful morning but a least I know I can run more or less problem free for the time being. I have 2 more on order and will keep them in the car as spares.

Regards
Dave

98.76

That is about 2 gallons (8/5ths) of Johny Walker Red in AZ!!!!

Glad you have it sorted.

John

[VirginiaF1]

Originally Posted by Dave Colangelo

So it was the DME relay...

Luckily the 933 uses the same relay so they happened to have one in stock.
Any one want to guess what it cost me...

98.76


Dave

Glad you're up and running but for how long is the question, ya?
Not to dowse your joy, but previously your car ran well for a short time before failing again, no?
Was the dme relay from the Porsche 933 or the 993?
Hoping your solution sticks mate.
GLWR

[Gawernator]

He meant the 993(911). Glad you figured it out man. I've never had a DME relay fail (yet) but I ordered one from Rennbay to fill up an order and sadly I got a URO relay from them. I swapped it in and it works fine so far, I still have the original relay in the glovebox.

[Dave Colangelo]

Originally Posted by VirginiaF1

Glad you're up and running but for how long is the question, ya?
Not to dowse your joy, but previously your car ran well for a short time before failing again, no?
Was the dme relay from the Porsche 933 or the 993?
Hoping your solution sticks mate.
GLWR

My mistake I did mean 993(the last air cooled 911) since it shared the same style ECU it shared many of the electronics. Porsche often did this and its why some the electronics in the cars seem wonky or backwards. As for the short time, this was all a result of the DME relay. I had been swapping it out with my old one that happen to still be in the car and was intermittent. The actual issue was that I had 2 intermittent DME relays and in this case
.5 + .5 != 1
On any note I think the root of the problem is actually heat. The past few days have been very hot and when I opened my fuse box yesterday it was quite toasty. I think the relays were simply overheating which is why I mentioned putting a heat sink on them. I will post a pic later of the emergency jumper I made on the side of the highway its quite comical.

Words of wisdom for all: Carry at least 2 spare DME Relays at all times! And a well made jumper!

Until the next issue...


Regards
Dave