medicis

Hi all. Although I've been a member for about a year this is my first post. So I'm bound to say something stupid. I've learned a great deal from this list and information from it has helped me put on a timing belt and porKensioner, install motor mounts and many other smaller tasks. (Roger has also been a big help) But in my current situation I need some advice.

About five days ago while driving about town, my 1986.5 simply quit abruptly about eight times. Each time, it restarted easily and kept going and then seem to be okay for a while. It didn't do it during the next day and I had to lend it to my son to drive to school for two days (he was very pleased) while I used our truck in the process of fixing his '93 Saab 900 Turbo rag top so he'd be able to drive it today (Saturday) to visit his girlfriend in Charlotte. Now I didn't see the Porsche for two days because he stays with his mother on those days and when he returned it to me it was running pretty terribly (apparently missing on a cylinder or two with very little power and, oddly with the headlights not working!?). He's only been driving for a couple months and frankly, was pretty clueless that anything was wrong.

After reading a number of threads on the list I decided to first check plug wires and coils (I redid the wiring when I did the timing belt) but I did find a connector under the left side of the air filter assembly where the wires had frayed (and I'm not sure yet which connector that was) and fixed it. Also checked the MAP I and it looked okay (previously I had cleaned it). Because we had had a bad run of gas in Morganton I also decided to replace all the plugs and refresh the gas. Well, I got it running and it seemed to be running on all cylinders though not as smoothly as I might like and while trying to drive it up my steep driveway the power in the engine was very reduced-it was a struggle to get up it versus the usual zooming right to the top.

So now I'm in the position of looking at the fuel pump and filter. I did the voltage checks at the relay and at the pump after cleaning all the connections and get about 11.70 V at the pump with the car not running and over 13 when it is running -- I don't understand that and maybe somebody knows whether that's normal or not. And I have yet to tackle the fuel filter. Some folks on discussions regarding the fuel filter think it may make a substantial difference and others think not. So I'm wondering if I should just replace it or if there is a way to clean it out a bit just to see if that is the problem. But my main question at the moment is about the compression. I did a compression check and got the following readings from the back forward:
#4: 170 #8: 178
#3: 179 #7: 180
#2: 169 #6: 175
#1: 180 #5: 178

Now, I'm used to working on Austin Healey's, Triumphs, Jag XJ-6's (I had only one other Porsche and that was a 912 back in 1973) and the normal miscellany. and the discrepancy posed by #2 does not seem so outrageous. But a good friend of mine who has raced in the past and workedon many more cars than I have expressed the view that #2's compression likely signals a valve job needing to be done. Now you can imagine, that I really don't want to do a valve job especially with winter coming on and me with no garage at the moment. I'd really like to put that off for a while if I can and don't really know whether it will really be needed anytime soon.

So, any help with advice is surely welcomed. And any thoughts about why the power overall would be so reduced as well as advice regarding the compression ratios would be most helpful. It seems like most of the folks on this list are pretty savvy and know far more than I regarding this beast (this word is used lovingly) as I am such a novice with this complicated, yet gorgeous and exhilarating Porsche.

(Oh, and mysteriously, the headlights started working today... ??! ..by the way, I did fix the Saab and my son is right now down in Charlotte with his girlfriend ... So I can feel successful about something .... :-)

James Bailey

You realize that you have two ignition systems and if one has an issue like a bad coil wire the car will run on 4 cylinders....two on each bank. It will be somewhat rough and only have 1/2 its normal power. If your car still has cat convertors driving it that way can set the car on fire. If a cylinder is NOT firing but still getting fuel it can wash down the cylinder walls giving a somewhat lower compression reading. As long as you have over 100 lbs compression most engines will still run.

Mrmerlin

ad some water absorber to the fuel and or drain the tank from before the pump and see if there are contaminates.
You compression readings are great,
dont touch anything if all were close to 170 and one was 80 then i would worry

Mark SF

Yeah I had an XJ6, an 87. Compressions were 120-130 across the 6 cylinders. I certainly wouldn't be worrying about 175. In fact, 175 to 180 is a very tight variance and indicates an engine in excellent shape.

medicis

Thank you all for your welcome information. At least I don't have to worry about doing a valve job....whew! The last time was 8 years ago on a F150 six cyl. And, frankly, I'm sort of afraid of the 928 complexity.

I exchanged my fuel filter for one I had on our '82 928 and it ran a bit better - with all cylinders firing (at least most of the time) but power was still really low and I could barely make it out of my very steep driveway (it usually roars to the top). I had put some Lucas additive in the gas and filled from a half tank to full with premium. No luck.

What are the odds on the pump vs fuel regulator?

WICruiser

Check your fuel system pressure at the front end of the passenger side fuel rail.

Given the intermitent nature of the problem it could be that your fuel pump is choking on something that causes it to stop pumping, or not pumping enough fuel resulting low pressure and therefore low fuel delivery when the injectors fire.

Landseer

I think there is still an electrical issue.

How did you address grounds? Two critical ones are at the back top of valley, and an obscure one located on right fender well just exactly below the 14pin connector for grounding the ignition amps.

Did you remove and clean CE panel?
Lightly clean inside each distrib cap?

We've seen two MAFs be taken-out completely via cleaning with MAF spray, BTW. I'm very leary of doing so. One of the MAF rebuilders cautions against it also.

cpayne

Had something similar happen the other day. Landseer came over and we did this.
Get in a very dark place no light. Shroud your eyes and look for blue strobing at each coil and plug wire. If you see it then replace the wires. or possibly coils.

fraggle

Does 86.5 have the same throttle position switch as 87+? The wire under the airbox sounds like that or the crank position sensor. If the cps was (is?) Intermittantly shorting to the block, you can get random stalls. I did!

Landseer

Yes to TPS. And we've seen frayed maf wires and frayed cps wires take the car down randomly.