strange power loss problem need help

krichard · krichard's Garage

Last Friday on the way to work as I was accelerating to highway speed there was a sudden but quick loss of power that lasted about half a second then everything was normal. I was in 5th gear and almost to 3k rpm. I after nothing else abnormal happened on the way to work I thought I imagined it. Well today I was out driving and I'm cruising at 3k rpm in 5th and the exact same thing happened. sudden power loss for about half a second then back to normal. I was at constant speed this time though. The weather was similar to Friday, misting and mid 50s. The car is an '88 completely stock. I don't even know where to start so any help you can provide as to where to start would be a great help. Thanks.

kstylianos · 08:37 PM

It sounds like an ignition or fuel issue, both regulated by the DME. I was helping a friend troubleshoot this exact same problem with his 964. If you search the Rennlist forums for these symptoms, you'll see alot of references to a faulty DME relay.

krichard · krichard's Garage

anyone else had or heard of this issue?

Jeff · 11-10-2003, 11:02 AM

Kerry, Had the same thing happen to me. Turned out to be my Cylinder Head Temp Sensor. You can test the sensor using a multimeter (don't have ohm range in front of me, but I can look it up later if you need it) but, if you have the one wire (instead of two) sensor still in the car it should be replaced.

scottb · 11-10-2003, 11:08 AM

If the DME relay and cylinder head temp sensor have not yet been replaced in your car, I'd replace them both right now. DME relays will fail, it's only a matter of time, and the old style CHT sensors have been replaced with a more reliable unit. Replacing both will most likely solve your problem, and upgrade the car in the process.

krichard · krichard's Garage

I have a spare DME relay and will change it out. As for the CHT sensor is this the right part number for the one with two wires : H-606-915-00? That is the one that pelican sales.

donnieknoxville · 11-10-2003, 11:22 AM

Definately replace the temp head sensor first, and then the DME. I spent $1,000 in labor diagnosing this EXACT problem on my 1987 Carrera Cab. Worst case is you spend $45 on a DME relay and $80 on a temp head sensor that will eventually go bad anyway.

In my casem, they strapped it to a dyno and did every electrical test imaginable. It wasn't until a Pelican participant suggested the temp head sensor that I demanded my wrench try that. Just before ordering the part, they were able to recreate the failure on the dyno in the temp head sensor. Once replaced, it ran like a champ.

Don

scottb · 11-10-2003, 11:37 AM

I don't know if that's the right part number, but the new style CHT sensors are two-wire units. There's a tech article on replacing it. It's a bit of a PITA, but worth doing.

As for replacing the CHT first....I'd do both if I were you, especially if the DME relay has never been replaced on your car. It's a cheap part, which makes it cheap insurance!

Jay07 · 11-10-2003, 12:05 PM

I have had simular problem. I had a loss of power at about 5,000 rpm. by a process of elimination I have worked out that it is the fuel that I use.
Try a fuel additive before you try anything else!

Jacob
'87 Carrera

ChrisBennet · ChrisBennet's Garage

Like everyone said, the DME relay and old head temp sensor are likely culprits. The test of the head temp sensor isn't reliable because the failure is usually intermittent. I think the old sensors ground through the engine and the new kind have a dedicated ground wire. If it is the old 1 wire style you should replace it unless you want to wait until it strands you. I think it a good idea to replace the DME relay before it starts giving you trouble. Put the "known good" one that you remove in your glove box or tool roll for an emergency.
-Chris