87 with very intermittent cutout

gr8fl4porsche · gr8fl4porsche's Garage

Saturday in St. Louis was beautiful! Almost 70 degrees with the sun shining. Finally got to wake up sleeping beauty and take her out for a nice 4 hour cruise.

Here's the problem. I have a cutout problem. Every once in a great while - maybe once every 3rd time I drive the car, I will loose all power for an instant, then its right back to running perfect. Normally happens under hard acceleration. The motor will be pulling very strongly then all a of sudden a total cutout, enough to slam one forward against the seatbelt, then come instantly back on.

I thought I had this problem fixed last year.
I have new plugs, cap, rotor, ground at motor is clean and secure,
previous owner has updated the cylinder head temp sensor, dme relay is new, fuel filter is new.

The obvious possible culprits are ground straps up front and at the tranny, bad cht sensor, possible o2 sensor, connections within the dme, and maybe the plug wires which are original with 86,000 miles.

Since the car runs so well 99.9% of the time - which problem area would one check first? Its hard to tell if the issue is resolved since it is so intermittent.

Anyone else have this problem?

Don Plumley · Don Plumley's Garage

I had a momentary, intermittent surge under load in my 87. Does not sound as severe as you describe, more of a hesitation than a cutout. Turns out it was a bad spark plug (and a fairly new one at that). Had to be diagnosed on some sort of ignition analyzer.

Sorry can't be more help...

gr8fl4porsche · gr8fl4porsche's Garage

Thanks for the reply Don.

This problem occured before and after new plugs.

Don Plumley · Don Plumley's Garage

When the wrench was debugging my problem (after I tested all the sensors, broke and replaced the AFM...), the first thing they suspected was fuel delivery, so they tested the fuel injection system pressure, etc. A cutout seems like a) loss of spark or b) loss of fuel. I've seen somewhere on this site a DME debugging list/fault tree. Will try to find...

Tim Polzin · 03-10-2003, 08:29 AM

My Carrera did exactly this. Mine turned out to be a broken wire at the connector to the CHT.

Tim

88911coupe · 03-10-2003, 09:21 AM

Mine did the same thing and it turned out to be an almost invisible cold solder crack in the DME unit. The Porsche Dealer here in Dallas was quite happey to replace it for about $2,000 but with advice and help from this board I fixed it myself. If you do a search you'll find more than one thread on this subject. The fix was not hard once I knew where to look. You could probably just remove the DME and take it to a local electronics place and then let them fix the solder if you are not comfortable doing it yourself. Bottom line...don't buy a new DME if you don't have to.
BTW, it could be your cyl temp sensor or a faulty DME sending unit, both of which are pretty easy fixes.
Good Luck

Rick Lee · Rick Lee's Garage

Could be your fuel pump is showing signs of dying. Mine died completely and suddenly though.

andyu911 · andyu911's Garage

I had the same problem as you guys about three years ago. Worse yet, it cut me during the bank in PIR. Replaced rotor, spark plugs, fuel pump... It turned out the DME defected. I had a Borsch technician repair it and never have any problem.
Andy
'87Carrera

jtratza · 03-10-2003, 10:30 AM

My 1987 was giving me fits a little over a year ago with a similar malady. Turned out to be a bad connection in the short wiring loom between the DME and the Mass Flow Sensor unit that the previous owner installed. I also recall having a similar problem several years ago that turned out to be the throttle valve switch. Cost for switch is minimal. Cost for new loom, all 7 inches, was $90.