944 NA stops at 4K RPM
09-12-2018 | 09:29 PM
#1
Thread Starter
4th Gear
Joined: Sep 2018
Posts: 4
Likes: 0
944 NA stops at 4K RPM
Alright, so I’ve got an issue with acceleration at 4,000rpm.
1988 944 NA
The symptoms:
car starts, idles and drives fine. But when accelerating it will not go past 4-4,200rpm and when it hit that point it falls on its face like it hit a rev limiter. And this problem has no affect on throttle position whether half open or wide open. It will only stall at 4K. Also it will accept 5-5500rpm if you downshift into it. Also, coolant temp is jumping around wildly after car has warmed up. (Don’t know if that is relative or not)
What I’ve done:
replaced all vacuum lines, J boot, have put two AFMs on it, new position and reference censor and gapped to .8mm. New DME rely, new DME temp sensor, had all injectors rebuilt and flow tested, new ignition system (plugs, wires, cap, rotor, coil, everything). Have pressure checked and flow checked fuel pump. Fuel pump filter is new. New O2 sensor.
1988 944 NA
The symptoms:
car starts, idles and drives fine. But when accelerating it will not go past 4-4,200rpm and when it hit that point it falls on its face like it hit a rev limiter. And this problem has no affect on throttle position whether half open or wide open. It will only stall at 4K. Also it will accept 5-5500rpm if you downshift into it. Also, coolant temp is jumping around wildly after car has warmed up. (Don’t know if that is relative or not)
What I’ve done:
replaced all vacuum lines, J boot, have put two AFMs on it, new position and reference censor and gapped to .8mm. New DME rely, new DME temp sensor, had all injectors rebuilt and flow tested, new ignition system (plugs, wires, cap, rotor, coil, everything). Have pressure checked and flow checked fuel pump. Fuel pump filter is new. New O2 sensor.
09-13-2018 | 02:24 PM
#4
Thread Starter
4th Gear
Joined: Sep 2018
Posts: 4
Likes: 0
The cars cat has been removed so that should be a non factor. The timing has been checked. I’m leaning towards broken valve spring or bad DME.
Any good trobleshooting or ways to get a good DME? Or overhaul exchange?
Any good trobleshooting or ways to get a good DME? Or overhaul exchange?
09-13-2018 | 06:49 PM
#6
Rennlist Member
Joined: Aug 2012
Posts: 1,794
Likes: 182
From: Discovery Bay, CA
Trending Topics
09-14-2018 | 06:57 AM
#8
Drifting
Joined: Jan 2012
Posts: 2,883
Likes: 348
From: New York & Indiana
[QUOTE=Eschirtzi12;15288152]
I’m in Knoxville TN. So if anyone local has one I could slave on.
I want to take a peak at the springs but was trying to gain more insight before I took the cam housing off and the timing belts again.
Check all the connections to the ECU. The square spring connectors to the AFM, Throttle Position, Reference Sensors. Etc are known problems, do not fit tight or engage tight. Wiggle each one, side to side, up and down, and push and pull to determine potential issues. If it is loose, then do a fix to prevent it from being loose.
Another source of problems can be the ECU ground connections on the bell housing. The bell housing us Al and the connector is Cu, large delta on periodic table causes corrosion, also the ground braided strap from body to bell housing. Remove and use abrasive paper to remove corrosion and add dielectric grease between bell housing and connector to mitigate corrosion.
I chased a no start issue for 2 days at a race weekend at Watkins Glen and the "experts " all said reference sensors when the symptoms pointed to something else. It was an plug engagement issue to the AFM, loose and causing one pin not yo engage. Engine started the fastest aftet securing the plug but anecdotal believe clesning the grounds also helpef
I want to take a peak at the springs but was trying to gain more insight before I took the cam housing off and the timing belts again.
Check all the connections to the ECU. The square spring connectors to the AFM, Throttle Position, Reference Sensors. Etc are known problems, do not fit tight or engage tight. Wiggle each one, side to side, up and down, and push and pull to determine potential issues. If it is loose, then do a fix to prevent it from being loose.
Another source of problems can be the ECU ground connections on the bell housing. The bell housing us Al and the connector is Cu, large delta on periodic table causes corrosion, also the ground braided strap from body to bell housing. Remove and use abrasive paper to remove corrosion and add dielectric grease between bell housing and connector to mitigate corrosion.
I chased a no start issue for 2 days at a race weekend at Watkins Glen and the "experts " all said reference sensors when the symptoms pointed to something else. It was an plug engagement issue to the AFM, loose and causing one pin not yo engage. Engine started the fastest aftet securing the plug but anecdotal believe clesning the grounds also helpef
09-14-2018 | 11:20 AM
#9
Burning Brakes
Joined: Jul 2014
Posts: 1,137
Likes: 8
All good advice given. I see you've checked fuel pressure and flow. Before you drive yourself crazy, I would suggest driving the car with a fuel pressure gauge taped to the windshield. Fuel pumps do strange things and best to check pressure under load.
One thing you haven't mentioned will it rev pass 4200 in neutral? If you think the valve springs are weak it won't make a difference whether you're in neutral or in 1st to 5th. Weak valve springs will cause misfire, backfire, poping through the intake/exhaust. Weak valve springs can be checked with a vacuum gauge.
As far as the temperature gauge fluctuation, on my early car it was cause by cold solder joints on the printed circuit board. I reflow the solder joints and the problem went away.
One thing you haven't mentioned will it rev pass 4200 in neutral? If you think the valve springs are weak it won't make a difference whether you're in neutral or in 1st to 5th. Weak valve springs will cause misfire, backfire, poping through the intake/exhaust. Weak valve springs can be checked with a vacuum gauge.
As far as the temperature gauge fluctuation, on my early car it was cause by cold solder joints on the printed circuit board. I reflow the solder joints and the problem went away.
09-14-2018 | 12:16 PM
#10
Thread Starter
4th Gear
Joined: Sep 2018
Posts: 4
Likes: 0
Ok - I’ll try to go wire by wire again on the AFM and associated parts.
Im going to take apart the ECU and look at the solders and resisters. See if there is any water damage.
The car will not accelerate past 4/4200 rpm in any gear, N - 5th, wether it’s 5mph or 90mph.
Im going to take apart the ECU and look at the solders and resisters. See if there is any water damage.
The car will not accelerate past 4/4200 rpm in any gear, N - 5th, wether it’s 5mph or 90mph.
09-14-2018 | 01:42 PM
#11
Rennlist Member
Joined: Apr 2011
Posts: 3,432
Likes: 154
From: Elizabethton,TN
You stated that the coolant temp was erratic. You might want to swap out the sensor, to eliminate that possiblity. they're pretty cheap 20.00 bucks or so. I think I'd do that before cracking open the ECM..and letting all the gremlins out. Could also be a broken wire between that and the ECM. A bad coolant temp sensor can cause all kinds of hair-pulling...
