robmeister951

The head is off (bent valves...don't ask) and I'm looking at the piston tops and see that the carbon build-up pattern seems strange. (See pics!)

This car has always had problems when starting when hot (i've had it since 1998). Cold start is fine. Hot start after being off for 15 mins or less... No problems. Try to start after leaving it for over 30 mins and less than 2-3 hrs! It would take 4 times as many turns to start.

It seems to me that the injectors have been leaking? Anyone agree with this diagnosis?

Thanks

Rob
86 944NA

Bill.e1

Rob,
Injector leaks effect startup and idle mostly and these are short-duration events. If there as enough fuel to clean the pistons, I'd expect to seen evidence of poor cylinder lubrication on the adjacent wall- discoloration and vertical scoring that is light and consistent. You may even see some aluminum erosion e.g. the "dead Vega syndrome."

I've seen similar on cars with bad head gaskets- antifreeze cleans carbon like no tomorrow.

I think the motor was just running very rich or burning oil and the last two were leaner or cleaner. Most unleaded burning, computer controlled cars have much lighter color deposits.

Hope this helps,
Bill

Zero10

I've seen similar on almost every 944 engine I've opened up. I have various guesses, but nothing concrete.

robmeister951

Hi Bill,

I had a bit of a think about the carbon deposits on top of the pistons after I wrote the post. I have used Techron Fuel Injector and combustion chamber cleaner on this engine for the last 5+ years (one bottle every 9 months or so)and I think it might have had a role in removing some of the carbon.
The engine has just under 250,000 km on it and the head has never been off.

The piston on #1 cylinder (the one with the least amount of carbon) I suspect may have had a leaky injector.

That's the theory for now.

I plan to get them all flow tested and serviced in the next week or so.

Rob

robmeister951

Zero, I'm glad to hear that. I was worried about the one piston that was a lot cleaner than the rest. The cylinder walls look very healthy so hopefully there is no problem.

The head is a different story, all valves and guides are being replaced and the head is going to a machine shop soon for a service.

The engine was not burning much oil, less than a quart per 1000 miles.


Cheers

Rob

Peckster

My car had the cool start problem but it eventually went away as I replaced parts that needed replacing for other reasons. Still not sure what the magic bullet was, if there was one.

I think a professional injector cleaning was the biggest factor.

That stuff you use while they're in place didn't do a thing that I could tell.

gtroth

Hot start problem for me was solved with new FPR (fuel pressure leak down was way too quick w/ bad one). I'll bet a bad injector could also leak down.

robmeister951

I will put that (FPR) on the list after I get the engine together. Dropping of the cylinder head with new valves, guides, seals to the machine shop this arvo, can't wait to get it back.

BTW, anyone have recommendation as to how to get the carbon deposit off the pistons?

Thanks

Rob

86 944 NA

gtroth

Yeah, when you get it all back together, if you can , put a fuel pressure guage on your fuel rail before you swap out the FPR and test according to clarks- just so you know for sure.

robmeister951

Hmmm, I' don't have a fuel pressure guage, I might have to just replace the FPR and be done with it.

The injectors were professionally cleaned by PO just before I bought it(1998).

Replaced the fuel filter, fuel check valve, engine temp sensor, spark leads, dist cap, rotor, spark plugs, all that made no difference to the hot start issue.

I will do the FPR and the O2 sensor(already have it) after the whole thing is back together and running.


Rob
86 944NA

Bill.e1

Rob,
I'd listen to the people with 944 experience before me. It sounds like your deposits are fairly typical of the breed. A "quick and dirty" check for FPR/injector leaking is to shut the car down, wait half an hour, and loosen the fuel rail end cap. Spec is some number after twenty minuts so if you get a vigorous squirt, your system holds pressure. If you get nothing then a little dribble once the cap is really loose, then you have leakage- either at an injector, the FPR, or the pump check valve. THe mid-time hot start issue is a classic symptom of leakown.

A wise man once said 3/4 of all carb problems are ignition problems. This was especially true during the points plus carbon wire days. I'd change that a bit today and say 3/4 of all fuel problems are electrical- sensor, ignition, corroded connections, old capacitors.

Last but not least- a fuel pressure gauge is cheaper than an injector. Buy one. I find nagging concerns like whether the pressure is right can suck the joy out of an old carl. Like the bank robber in Dirty Harry said- " I gots ta know."

Have fun,
Bill

PS- I converted my FPR to adjustable:

http://home.comcast.net/~eastmanb1/9...944-mods4.html

Good idea? Probably not but if I don't use the machinery occasionally, my wife will want them gone.

Tom Carson

a similar problem with mine a few years ago…turned out to be crank sensors

cleaned & reset…no more starting problems !

robmeister951

Thanks guys. I will make a note to test for fuel pressure and also crank angle sensors. Got a whole heap of work to do before that.

Cheers
Rob