930 just wont run right.. please help!

[air-cool-me]

i have a 79 3.3L with sc cams and 8-1comp its in a 77 with only the CIS pump up front..

it was rebuilt 6000miles ago.

at idle and part throttle under no load cyl # 5 fires intermittently.. sounds like a exhaust valve not seating but the heads were rebuilt.

also i have cold start issues, the car will start on only a few Cyl at first, and idle at 700rpm.. then a slowly climb to 950 as other cylinders come on.

the weird thing is 1 in 10 starts it will jump right to 1200 and be firing on all six.. sounding wonderfully... but after a minute or two it will drop to 900 and start coughing again..

i have\had..

mixture at 13.5 idle and 10.9 under boost,the fuel distributor rebuilt, fuel injector checked(not GREAT but ok), fuel lines switched,Don Jackson's went over the fuel system, spark plugs changed, plug wires swapped, leak-down 3%, control pressures checked, vaccume leaks checked\fixed

adjusted valves last 4000 miles ago(my first time.. my mechanic is now re-adjusting them ito see if i screwed up.. )

Any ideas why it breaks up at idle and when under no load? i need all the help i can get..

-nick

[dyerkes]

Nick,

My recommendation would be on the fuel system. Has your fuel filter been replaced recently? Although I don' t think it would impact you at idle, but I would be concerned about running only one fuel pump when under load. If this is a '79 car it should have had both fuel pumps...right? I'm assuming that your fuel pressure was verified and check out ok. Lastly, if your injectors are questionable, I'd replace them. At idle your running less pressure, such that if you have partially clogged injectors your likely to be running too lean on those cylinders that have the worst injectors. You might want to also try posting on www.rennlist.com .

Good luck,
David
1986 911 Turbo

[air-cool-me]

already posted on rennlist's turbo forum

fuel filter was replaced when the motor was rebuilt less then a year ago.

the fuel pressure was just fine and checked out within specs with only one fuel pump.. the car was a midyear so it did not come with a second fuel pump. I have not spent the 500$ on a new second\turbo specific fuel pump.

the Injectors were checked out by Don Jackson enterprises on a bench tester. Cracking pressure was fine and i was told they were "OK". They are a professionals and i assume that they would have recommended replacement if that was necessary?

thanks for the help David. i need all i can get on this puzzler!

[air-cool-me]

Thank you all very much for trying to help! i am totally baffled by this!


i pulled the plug lead to number 5 and i think thats the cyl that is misfiring because pulling it has very little effect at idle... the idle sounds the same but it starts to backfire..

that was the only cylinder that i did the compression and leak-down on. I cant remember the compression numbers but the leak-down was 3%.

I had don Jackson enterprises (in Phoenix) pull the injectors and bench them. the cracking pressure was fine and they said they were not great.. but sprayed "ok" not enough not to cause a problem. I will get back on the phone with them and get more info. I do not know how to test the injectors on my own with the metal lines... with plastic on my early SC i was able to pull them all out and aim them into a bucket!

i have not checked the fuel accumulator for holding pressure. or i might have and cant remember (i have been working on this for a LONG time) i will check the record of what i have done tonight.

the fuel head was rebuilt by Fuel Injection corporation. It was rebuilt when the motor was.

During the process of troubleshooting i cracked the #5 injector line (the banjo fitting)at the fuel head to see if i had fuel pressure and it did not "spert" like the rest of them when i cracked the line. Also there was no change in idle(indicating a dead cyl) so i sent it back to FIC and they put it back on the bench.

i was called by there "senior tech" and told that there is nothing wrong with it. So i put it back on the car and nothing changed...

it will be so nice if i can solve this... when holding it at 3000 when warm you can just hear the slight misfire.. 3 months of attempted diagnosis is driving me nuts!

[hobieboy]

I think you want to first isolate the problem & make sure you are attempting to fire all cylinders at all times - check your ignition stuff first (wire/distributor/vacuum hose/...). If the system is attempting to fire all cylinders then get to the fuel system.

[air-cool-me]

i pulled all plug leads individually and got the S* shocked outa me.. only #5 didnt have an effect on the sound of idle.. although it did start to backfire.. but there was no RPM drop and roughness like when i pulled the others..

and i have spend hours looking for vacuum leaks.. in addition to the guys at Don Jackson's looking for them..

plugs have been changed(a few times)

any more ideas?

i looked over my notes.. the system help fuel pressure for 2 hours so a check valve isn't a problem

thanks for the help-nick

[alwaysflat6s]

If I understand, this is all 3.3 engine, right? FIRST, I fear you are simply going to chase your tail until you have the fuel system correct to spec. This means getting a proper set of fuel pumps in the car. It is possible it will not help your problem. I PROMISE you that even if the current problem you are noting gets fixed you will damage your engine if you USE it like a 930 is intended. I know it hurts and it is quite expensive but you jumped to a 930 and you knew you were getting into the top of the food chain. The expensive of making a proper fuel system is nothing compared to what running a lean mixture on boost is going to cost. SO I urge you to fix this FIRST.

Then, based on what your have been saying, I suspect you will disover you have a problem with your fuel distributor.

BUT these things have gotta be right and in spec or you will end up destroying an expensive engine.
Good luck

[air-cool-me]

the permanently connected wide-band i have in the car says im richer then 11-1 as soon as the boost comes on... 13.2 or better before then. fuel pressure is to spec. i don't think i will have a problem with running lean and i don't see how that is a problem?

but im open to anything at this point... the front pump on an SC is the same as the front pump on the turbo... it will take me a bit of time to find the $550 to spend on a factory second pump.

and ideas in the meantime?

the fuel distributor was rebuilt when the motor was.(<7000miles) sent back at 3000 miles because i thought the very same thing.

Fuel injection corporation is the name of the company..

should i send it to them for the third time?

thanks for the help
-nick

[beepbeep]

Check for crack in phenolic intake spacer on cylinder #5. Spray carb spray around and look for leaks.

Cheers!

[air-cool-me]

Alright.. i will re-check valve adjustment and look for a leak at #5

[air-cool-me]

alright... i checked for vacuum leaks around # five and found none...


static compression numbers were around 120# if i remember correctly..
i did a dynamic compression test as the good Dr. instructed(porschePhD on rennlist)... this is what i found..


95psi on every cylinder except #5

#5 was 80psi.. there was 3% leak-down on this cylinder so I am guessing this is a valve adjustment problem? I adjusted the valves not to long ago but i will take it apart and have a 40 year veteran of 911's adjust them for me..

thanks to PorschePhD and his dynamic test....I might have to buy something at imagineauto!

[john walker's workshop]

dynamic test? 3% is great by the way.

[air-cool-me]

i was just about to call you and and ask your opinion Mr Walker..


well.. he said to leave the tester on and start the car up and let it idle... instead of pulling the fuel relay and just Turing it over..



he called it a "dynamic test"? i talked to a few other people and they said it was "old school"?

i hadn't heard of this till he said i should do it..

thanks.. I'm really glad its 3%

No, Bosch recommends dynamic as apposed to static. Pull the pull and place the compression tester in the hole. Start the car and see what the gauge does. You will be surprised what happens when running and under pressure. Compare those numbers across the board

Starting the car and it running with the compression tester in it is dynamic

Bet most have not even heard of this!
__________________
Stephen

[air-cool-me]

alright... the valve adjust is SPOT on....


i have used a ton of carb cleaner looking for a vacume leak and found nothing...whats next? i have no idea where to go!
HELP!
-thanks-nick