johntorg

I have just run two PCA sprint races at Roebling Road and have one more race tomorrow. I have the folowing problem: The engine cuts out after right hand turns. this is pretty consistant and happens every lap in pretty much the same places, all on the exit of right hand turns. It happens even with a full tank.

For those of you who know Roebling, it happens as I track out of turn 2, on track out of the carousel (turn 7) and on the straight after turn 9.

Background: I had a massive headgasket blowout on Thursday, but didn't have any engine cutout during my runs. I replaced the headgasket last night and have had the cutout problem ever since. I'm not sure if they are related issues.

I have jumpered the DME relay, but it didn't help. The car is an 84 944Cup car with a stock fuel tank. Fuel pressure is good when idling and revving the engine under no load.

Has anyone had similar problems?

Any help or suggestions for diagnosing the problem will be greatly appreciated.

Bri Bro

Check the connections to the AFM, TPS and the injectors to makes sure they are well seated. If you have an original engine harness, the wires going to the injector plugs could be brittle. This could cause an injector to cut out as the wire moves under G forces. The wire is normally worse close to the plug since which is close to the headers. You might have cracked some brittle insulation while replacing the head gasket. Strip back the outer sheath a couple of inches back from the plugs and see if any bare wires show up.

TedA

I wish I could offer some assistance. I have experienced the same problem recently at VIR (84 944 NA), only on right hand turns. Three day event, no problem day 1, morning day 2...car shuddering hard on the RH turns. After lunch car runs normal again for the duration of the event. No specific problem identified. Gas tank was full.

The one thing that we did do was check all the vacuum lines associated with the J-boot. Disconnect/reconnect, car got better. I'm not convinced this was the problem.

Please post back if you get it figured out.

Bri Bro

One other thought, check the speed and reference sensor plugs. The plug that goes to the sensor will fail over time, the plastic just gets very brittle. The engine harness side seems to last. This problem tends to happen when water gets into the plug and effects the signal which is a very low voltage/current.

And take off the J boost and looks for a tear. All major vacuum hoses also should be checked. Look to see if the AFM flap has any rub marks and is binding. If you have a spare AFM, swap it out. Good hunting.

Rich Sandor

I'll forward this to IanM - I think he was having EXACTLY the same problem.

aelliott

A bit of a long shot, but in the interest of covering all the bases...

I had a similar problem this year caused by the battery-to-alternator cable grounding out behind the engine. The clamp holding it in place had worn through the insulation, and the cable would touch and short in certain (right hand) turns and cause stumbles.

Eventually, of course, this abuse burned the rest of the insulation away; I was lucky to avoid a fire or serious electrical damage.

Adam

johntorg

Wow Thanks or all the responses. I will check out all suggestions this morning. FYI the problem is not just stumbling, but a total cut-out, sometime 2 or 3 in the same corner. It felt electrical. The wiring is original and 24 years old. It was obviously disturbed during the headgasket replacement, so who knows. I will post an update tonight. Its costing me 1-2 seconds per lap and makes for some interesting corner exits.

84-944

I had the same problem, 84-944. Check the speed senser wires/connections behind the motor. Replace them if you can, sometimes they look OK but they just don't work properly anymore.

Pull the plastic cap off the fuel rail and check each wire closely, I've seen one wear and ground out on the fuel rail.

If you've spliced into a fuel injection wire for an air/fuel meter, check that connection closely or just redo it.

This seems to be an electrical problem that shuts off the fuel delivery when the motor and wiring sustain lateral forces in right hand turns. You're not alone.

TedA

This is exactly what I experienced. I am not sure I have it fixed. Please report back.

johntorg

Update: The good news is that I finished the race (13th out of 20). The bad news is that I still have the problem. In the morning I cleaned the plugs for the speed sensors, the TPS and the the AFM, using a product called de-oxit. I thought I found a ground wire with a bad crimp, so I crimped it with a pair of pliers (no crimping tool available). I then added fuel to the tank. I did a 15 minute warmup session without encountering the probem. Unfortunately on the 3rd lap (of 30) The problem reappeared and stayed with me until the end of the race.

Tomorrow, I will disconnect the possible bad ground wire and see if the engine dies. I will inspect all the injector wires and go over every area that was disturbed when I replaced the head gasket.

What is weird is that the engine cuts out after I exit the corner, not while I'm in it. The carousel is a pretty long right hander that generates a lot of G force and yet its only when I accelerate out it that he cut-out occurs.

I guess the other good news is that my late night headgasket job seems to be holding.

IanM

Well, I think I have some good news for you. I had the EXACT same problem, and successfully solved it. It ended up being similar to Adam's problem as described above, except for me it was the power cable where it bolts onto the starter solenoid. The insulation just behind the connection was worn off, and it would ground itself against the body. The car would cut out momentarily after sharp right hand corners on the race track and at autocross.

That power cable comes very close to the body ("bellhousing" area behind the motor) right where it bolts onto the starter. Be sure to disconnect your battery before you do anything. Then disconnect that power cable from the battery and see if the insulation is worn through. Use heatshrink tubing to repair. Try to reconnect in such a way that the cable will not continue to hit and rub against the body.

Your symptoms are so similar to mine, I'd be surprised if you don't find this is your problem.

Good luck.

bgiere

Take the gas tank out and remove the "sock" inside. How hot is the fuel pump after a session?

RedlineMan

Indeed;

You need to be careful not only with the aged cable insulation, but it's proper routing. You will find many cars these days that have not had all the cable holders (near the block ground connection and on the bellhousing, for instance) reinstalled after major mechanical work. The factory does EVERYTHING for a reason, and these Adel clamps and other cable routing devices are quite purposeful.

The later cars had a number of revisions and updates for the proper routing of cables (mainly from the battery to the starter). It was found that high voltage interference was quite possibly interrupting the faint signals transmitted by the crank sensors, which caused all kinds of intermittent driveability problems. Cracks in old insulation can make this even worse!

Do you hear any "moaning" sound coming from the fuel pump area, or is it warm as Brant siggests? For what it is worth, it does sound very much like a starvation/cavitation problem that I have suffered for the last 3 years, intermitantly. Although my system is totally different than your stock one, the symptoms are identical.

Don't assume that this has anything to do with your head gasket situation. It might be totally incidental, and unrelated. Cars like to F with you like that.

M758

Yep,
I had the same issues on my 84 944 years ago. Pulled the sender and found a white plastic circle thing in the bottom of the fuel tank. It was actually part of the fuel filler neck and had broken off. It was I suspect plugging the hole to the small surge tank in the bottom of the steel tank. Anyway once removed the problem never came back.

BTW.. my car would run out of gas on corner exit. then come back after straighening the car out. I still had all electricals.

johntorg

Thanks for all the insight. The fuel pump is quiet and the pressure is good under no load. Unfortunately I didn't remember to look at the tach when the problem occurred (something about trying to catch the car when the engine cuts). I did change the starter a month ago, but I ran 3 track days without any problem since then. I am very sure that all the cable clamps are not in the original positions.