Shark Attack

holy crap son, what are you feeding that thing?

Mrmerlin

How old are the spark plug wires? if they are older than 5 years it might be time to rewire your car, as previously mentioned it takes a spark at the wrong time to send a fire impulse thus if the wires are old they might pick up a signal that was being sent to the correct wire and thus starting the flaming glory, also check the distributor cap/s if there is a tracking trail inside the or outside the cap you may have a hairline crack that will also let the spark jump, and check the distributor rotor, make shure it doesnt have any excessive play

spinaker

Thanks everyone for your input. Sorry haven't been online to weigh in here but I just got back from a two day out of towner with my SO and mandated, no internet.

It sound like there is some consensus on the cause of this little problem. I guess I am fortunate that I only dislocated the plenum from the rubber hoses and broke a small piece off of he plastic intake. I have a set of new hoses that I have never put on and I suspect that with that as a week point it saved a higher pressure build up and dents in my hood. I'll do a more thorough check in the morning and then a call to Jim for replacement parts availability.

The plug wires, caps and rotors are three years old with about 23,000 kilometers on them. I'll check the caps for tracks in the morning as well.

I'm afraid the cams are beyond my skills. I think I could do injectors but it doesn't sound like that is the root cause...or would that help to some degree?

Should I expect that if I put it all back together, this would happen every time I tried to start it or is this to be a random reaction from here on in?

Thanks again for everyone's considered diagnosis.

spinaker

Bump.

heinrich

I have not heard of this happening with other than 85-86 cars. Therefore IMHO the issue may be related to one of the unique qualities of the model, such as that the intake has so many opportunities for horrible air leaks. I know when I replaced my injectors the issue disappeared BUT that very possibly could be a result of my checking the intake for leaks as I reassembled it. How we ignited the intake charge ... that is another question. Aggressive lift and duration on the cams? 85-86 cams are more aggressive than their S4 counterparts, but GT and really early cars lift as high. Maybe a combination of factors. I'm confident that my wires were new and caps / rotors good.

spinaker

Thanks Heinrich. I'm going to carefully examine everything this afternoon. I know for a fact that the intake boots are poor and I will install new ones I have on hand. Is there any harm in my trying to start it after I put everything back together (before new injectors) or now that this has started it will happen every time I start it?

Bill51sdr

I've been thinking along the same lines H. This problem is peculiar to the 85-86 32V cars. Camshafts are different, perhaps there's an overlap causing this? I'm wondering what changes were made to the 87-on LH & EZF computers that could be curing a "crossfire" problem. Sure sounds to me as if we are getting ignition in a cylinder with an open intake valve & obviously this is bad. All the wires, caps and rotors were new'ish on mine and were ruled out as a problem when it happened to me. I had no signs of leaking injectors. I removed a set of Autothority chips as a precaution and did reset the cam timing. Problem never recurred, with me at least. Someone in Las Vegas owns that car now, so who knows?

John Speake

There's no differences betwen 85/86 LH/EZ-F and >87 LH/EZK that I know would be related to this problem.

I think cam timing is the most likely cause.

Big Dave

Changing the cam timing takes some effort, but checking cam timing with PorKen's tools is a 10 minute job. I suggest you buy/borrow a set so you can find out if you need to fix the timing.

spinaker

Everything back together and everything runs fine. In fact, the idle is lower and smoother suggesting I had a vacuum leak.

I would be very grateful for the opportunity to borrow the required tool to check the cam timing. However, Edmonton, Canada is pretty isolated from the mainstream 928 communities and I doubt anyone nearby has one.

I am now considering selling this car not withstanding how much it means to me. I feel that, with limited time to work on it and limited mechanical skills, it might be best to see it in a new home where it will be better preserved. Being a 5 speed with a virtually immaculate interior, it should be preserved and improved as necessary which has always been my intent. I've had the timing belt and water pump professionally done and myself have done new shocks, motor mounts, electric cooling fans and much more. It has 993 wheels with new tires and a new battery as well. As with all 928s. I'm sure there is much more still which can be done. This car has always been reliable and I've put almost 25,000 kilometers on it over the last three years in just summer work commuting.

I'll keep all posted if I make a final decision to sell.

Thanks again to all for your input.

the flyin' scotsman

Doug..........I have Kens cam timing tool. If you feel like a drive and its perhaps a little too mechanical for you let me know.

PS; perhaps interested if the price is right!

spinaker

Malcolm,

I should have known you would have the tool. I'll think about the drive. I need to be in Calgary where we're celebrating out 25th. I don't know if I would be forgiven if I took time out to check the cam timing on the 928.

I also wonder if I should be driving it with this problem.

I'll keep you posted.

the flyin' scotsman

No worries...........let me know if you want to borrow or we could do it together down here. Drive down one aft., let her cool off overnight and we'll get her set the next morn.

You and the SO are more than welcome.