Fanatic

I have a 944 Turbo that experiences a hiccup or stumble that is very intermittent. I can drive almost a tank full before this happens and other times it happens more frequently.

I'll be cruising along on the highway at about 75-80 mph (around 3000 RPM) then all of the sudden the engine cuts out, I can see the RPMs drop a bit, nothing significant enough to kill the engine but serious enough to catch your attention and jolt the car. At one point I thought it only happened when I would hit a bump in the road but that turned out false.

I haven't experienced it at full throttle just at a steady cruising speed. On one occasion it actually dropped to idle and in order to get power back on I had to lift off the throttle and re-apply. If I tried to give it more gas it would do anything.

Have any of you experienced this? Is it the AF meter or DME? I've replaced the TPS.

Your assistance is greatly appreciated.

porshhhh951

fanatic i have the same exact symtom that you do! I am very intertested in what is causing this and how to fix it! does anyone know what is causing our cars to hiccup?? it only happens to me when i am crusing at low speeds never under load or accleration.....and its sparatic....sometimes i can go for awhile without it happening and other times it happens more often....does anyone have any idea's????

Fanatic

Well I've swapped out the AF meter and DME relay with no effect, still hiccups (stumbles) at hwy speed.

I'll try the DME next.

Danno

When this hiccup occurs, is there anything that happens right beforehand? Like you hit a bump or you change the throttle ever so slightly?

Fanatic

Danno, it does seem to happen more often when I hit a bump on the highway or when I go over the divider strips. But it has also happened when cruising along on a smooth road. The throttle is steady when it happens.

Peckster

bad ground?

crazyracer

I have the same and my wideband sensor is telling me that I am running lean. Get a guru or vitesse kit and make a dyno run or buy a wide band sensor and adjust the whole thing.

porshhhh951

i cant be running lean my air/fuel ratio is perfect .......according to the gauge and dave lindsey just got through tunning it

reno928s

I had a problem like this happen to me. It was caused by a lean condition. Check your spark plugs, just to be safe. When I checked out my plugs the #2 cylinder plug ceramic was cracked. Easy check. Reno

dmoffitt

yeah that sounds ignition related, check the wires going to the coil, and your spark wires, and plugs.

crazyracer

You are not running perfect. Too lean, believe me, I am having a wideband sensor and when you tune the MAF "perfectly" then you can only do so at WOT, ask your supplier how to tune half throttle or cruising on those fine units.

porshhhh951

hmmm i just had a tune up done.....i can check but all of the plugs are new(cool blue wires) if i was running lean wouldnt it come out on my gauge?? i will all the connections tomorrow but i am still getting the condition does anyone else have any ideas about what it could be other than running lean and bad plugs....!!??? i mean i have new everything.By the way this condition isint new.....its been like this since i got the car back in feb...so the cause cant be the new mods this was a pre exisiting condition...help if you can.

thanks in advance.

adrial

TPS? Probably not..but hey you never know...

Danno

Yeah, check the TPS. Hook up a digital voltmeter to the white-green wire coming out of the TPS. Fully closed, it should be about 0.50v. Then slowly open the throttle and full-throttel should be 3.75v. It should also increase linearly without any sudden jumps or drop-outs.

TPS-velocity triggers acceleration-enrichment and switching to the WOT/full-throttle fuel-maps. If somehow the DME was sensing you've stabbed the throttle, it'll dump in a tonne of extra fuel. However, if it's a false signal and you're still cruising along at the same speed with the same air-volume flowing into the engine, this extra fuel will cause a stumble.

porshhhh951

hmmmmm danno i think you might be on to something.I will borrow my fathers voltmeter and check it out.....i will post my findings.