nocomment

Hello, I have a 944 that runs and drives great. Most of the time. The issue: when the car is cold it starts right up, idles perfectly at 1100 RPM, and pulls good up to about 3500 RPM(where I stop since the engine is still cold.) No signs of power loss or flat spots. When the engine gets warm the car pulls hard all the way through the rev range, and still idles perfectly, so the problem doesn't appear to be engine temp related. But slowly but surely I start losing top end power. I exponentially lose more the longer i drive. First anything past 5500 rpm sputters, then 5000, then 4500, and that's where the problem generally stops. The car will sputter and misfire and sometimes won't accelerate at all past 4500. The car idles perfectly during all scenarios, and this only happens when car is under load, revs just fine all the time.

If I use partial throttle i can get the car up to redline. I haven't checked the fuel deliver system but the car gets all it needs before the problem so that seems fine, unless the FPR could be failing as i drive it, could that be an issue? I pulled ECU and checked solder joint, all appear to be OK. I pulled DME relay and checked solder joints, appeared to be ok, but i re-soldered them just to be safe. No change.

I cleaned and re-sealed TPS, and checked AFM. Both work great and contacts are super clean.

I replaced the spark plugs since age of current ones were unknown. Problem got better, car takes longer for power loss to show up.

So air and fuel appear to be good, could this be a ignition issue? My plug wires have quite a bit of rub wear from no separators from PO but I've been using them since i first got the car about a year ago and this just now started happening. Dist. cap and rotor also appear to be good, and a faulty ignition coil would mean no spark, right?

Sorry about the long read, you guys are awesome. If you need any more information or i was unclear on anything please ask.

*UPDATE* I have noticed that the fuel pump gets louder as i drive it, when i start the car in the morning it's inaudible over the idling engine. 40 miles later the whine is very noticeable. Is this fuel pump or FPR related? But can a FPR be heat sensitive? Can a fuel pump be heat sensitive?

*UPDATE* Last time the car started to lose power I turned it off for about 5 mins to make a jumper for the DME relay for the heck of it. I then drove the car for 40 miles without any issues. Overheating DME relay seems highly unlikely to be a problem, but i've ordered a replacement anyway.

*UPDATE* I've ordered new DME relay and ignition coil, will replace and see if that fixes issue. If not next is distributor cap and rotor, and then FPR.

944Ross

Coils can be heat sensitive, I've had ones that would run for a mile and then quit; one that ran for 3 - 4 hours then would become erratic. Basically the windings would short out and reduce the number of active turns, reducing output.

nocomment

but would that cause gradual failure? Coil keeps getting hotter and hotter making problem worse and worse? Also, was your coil fine when it cooled down? Thanks for your reply

944Ross

In one case, my truck, it would start and go fine for about a mile, then start firing randomly. When the turns short, the power draw goes up and the coil would get smoking hot. (lower resistance)

Jerks and sputters usually point to spark, smooth but lack of power to fuel. Fuel filters that are nearly plugged can do some funny things.

nocomment

I'll replace my coil then and see if that helps, since fuel delivery isn't an issue when the car is cold or has gotten hot, and i replaced the fuel filter when I replaced my transmission. Is there anything else that could be getting hot and causing issues?

968workaholic

Swap out the cap and rotor to rule them out. Even though they can look fine they are notorious for causing odd issues. Sounds like a heat/load issue, which would point to ignition imo. What's probably happening is that spark is getting blown out at high load, that's my .02 at least. Good luck with it

nocomment

Thanks, i forgot to add that it only happens under load. It's probably time for a ignition overhaul anyway. Thanks for the help, when i get parts I'll share how it goes.

konakat

Could be the injector driver circuit in the DME overheating. Try borrowing a good DME and see if the problem goes away.

nocomment

wouldn't that cause issues throughout all rev ranges or the system to completely shutdown? Loss of power is relatively smooth, and point of loss gradually decreases. I'm new to the Porsche scene, but I'm planning on getting involved in my local PCA starting this weekend and maybe there will be a 944 guy who will be willing to let me try his DME.

Jacob AbuKhader

Ever solve this? My just started doing a similar thing. Feels like the engine is fighting something.

walfreyydo

Exhaust or intake restriction? Still running original catalytic converter? Could be clogging up your exhaust - worth a check.

Did you ever test the fuel pressure like we had asked in your other threads?

Jacob AbuKhader

When I got home from work I started running a couple very quick checks, and noticed the exhaust was EXTREMELY hot. Also had noticed a bit of rattling from under the car, I ran it to my friends shop to have him check the cat, and it was completely shot. So my car is on an impromptu cat delete. Completely fixed the problem and then some. My car throws me back into the seat now, and revs freely and powerfully all the way to redline.

When the cat was pulled it was the rattle and some nice BBQ charcoal came out when tapped.





Still need to actually check fuel pressure numbers, i just need to order the gauge kit from Lindsey. Needs to be verified in order to rule out something else that killed that other pump, and could potentially be the cause of this failure as well, as this catalytic converter was less than 10 years old.

Jfrahm

I recently dealt with a friend's car that would run fine for 10 minutes or so and then slowly fade. Turned out to have suspended flakes of something (old gas?) in the tank which would gather up on the tank sock over time and starve it out.
It's possible that E85 will dissolve this stuff but might take out the old rubber fuel lines in the process (which you might want to replace anyway). The tank sock might or might not survive.