lost fuel mixture and vacuum

[danielt]

911 engine experts,
Got a new challenge for you. While driving to work the other morning, the car began to stumble and run extremely rough while cruising at 3000rpm. It would not hold an idle and would die instantly. After leaning out the fuel mixture for >30%, I was able to get the car to run, but idle was now at 2200rpm (normally 800rpm) and still extremely rich. The car has no power and seems to get weaker with more throttle. I limped the car back home and pulled the plugs. All are carbon black. After putting the plugs back in and restarting cold, it would idle at ~1200rpm with manifold vacuum at only 5-6". Normal vacuum at idle is 12-13". I originally suspected that the vacuum line for the fuel pressure regulators snapped, causing both the vacuum leak and the overly rich condition. That checked out clean. At this point, I have not found an obvious vacuum leak after checking all the joints from the heads to the throttle body. I have checked the fuel return line and it is not blocked so the fuel pressure should be controlling properly.

Current guesses:
1. One or both of the cams has slipped and is off. I would expect this to screw up the vacuum, but would it make it rich, too?
2. It is demon posessed and will require a priest to get it running right again.

Any direction and help is extremely appreciated.

Current condition of the car:
Big bore 3.2L
cams reground to 964 profile
Intake from an 1989 Carrera
Electronic fuel injection from SDS-EFI.

no issues like this for the first 10,000 miles on the rebuild.

Thanks,
Daniel

[Rot 911]

Not sure what your problem is, but I seriously doubt a cam skipped a tooth on the chain. The 911 is an interference engine and by now you would have some bent valves or a hole in a piston if a tooth skipped.

[tab tanner]

Check the vacum boot, between the AFM and the TB

[danielt]

Tab,
I no longer have CIS on teh car. It is using an 1989 manifold with EFI.

Kurt,
I've 9.5:1 JE pistons with massive valve reliefs. When I did the mock up, I had a ton of clearance (>.15") What if the chain tensioners went slack or a chain ramp broke? If you can't tell, I'm really fishing before I tear into it...

Thanks,
Daniel

[danielt]

Still troubleshooting. New info:
compression check:
right bank - 150psi +/-5
left bank - 125psi +/-5

Sparkplug reading (will post pics in a few minutes)
right bank is dry black soot on all 3 plugs indicating a rich mixture. Have a gas smell.
Left bank is clean and wet with gasoline. Almost like they aren't firing. all 3 are the same.

If I unplug a plug wire from the right bank, the engine stumbles.
If I unplug a plug wire from the left bank, no change.
It is a waste spark ignition system (Like TEC, etc.) with 1 coil firing 2 cylinders.

I'm back again to question cam timing due to the whole left bank having a different compression pressure reading than the right bank. I don't know what else could cause that...

[danielt]

Right Bank:


Left Bank:

[James Brown]

Sound like a vacuum leak not mechanical failure. What EFI programmer are you using (motronic or aftermarket) Check with carb cleaner with the engine running around the intake and all vacuum lines, how are the brakes?

[danielt]

That was one of the first things I looked for. I sprayed the intake down with carb cleaner trying to find a leak. I am using a 1989 Carrera manifold with SDSEFI system. When it went bad, it was instantaneous. I was cruising down the freeway at 75mph, and it just died...
Only way I could get it to run was to lean it way out...
A vacuum leak would lower the manifold pressure causing the EFI to increase the fuel delivery so that is a potential for making it run rich. However, that would not explain the bank-to-bank delta in compression test....
Never hurts to check it again, so I'll add that to the tests for this week.

[James Brown]

The Simple Digital system has some fault lights but does not rely on a laptop to program. Wonder if something went haywire in the CPU? I know you checked it but you might want to check with SDS and see what they think as you said it happened all of a sudden. Might be a simple sensor.

[danielt]

Thanks for the feedback James. I have contacted SDS and they gave me a list of things to check on their side. I was suspect of the manifold pressure sensor for a while, but it checked out good. I was able to use a hand vacuum pump and the readings corresponded correctly. I've also opened up the CPU box to see if I had any blown/burned drivers for the fuel injectors, but they all look normal. No signs of overheating or overcurrent on the board.

[Porsche Head]

This is old school stuff I remember for working with my neighbor who was a stock car racer.

If you pull a plug and nothing happens then it means that cylinder is dead, usually no spark or bad compression etc. The plugs tell the same story, they look rich. Why would the one bank be rich is the question, either it is over fed or the spark is not getting there. Sorry if you checked but is there spark? Personally I have had bad exp with the EXP or mutli tip plugs, ran horrible sent them back.

Check the spark and replace the plugs.

Cliff

[danielt]

Cliff,
I pulled the plug and grounded it to the fan housing and I have spark. I agree with your assessment that it acts like a dead cylinder, the kicker is it runs very smooth for only 3 cylinders, if that is the case....

[Flat6pac]

Thats why when you jump time from a dropped tensioner you can still get home, half the engine will get you home.
Bruce

[danielt]

OK, that settles it. I've got a handful of things to double check, then the cam covers are coming off this weekend. Just ordered new gaskets from PP.

[Gerziebaker]

Was it a dropped tensioner?

[James Brown]

the hydraulic or mechanical cam chain tensioners. They keep the cam chains tight. If they fail, the chain slacks and cam timing get's out of wack.

[danielt]

Baker,
I don't know yet... I pulled a muscle in my lower back doing all the compression testing the weekend before. I've got the engine dropped down and about half way through removing the nuts on cam cover last weekend, then, I couldn't sit on the floor any longer. Spent the next 2 days in bed or a chair taking muscle relaxers... getting old sucks!
Feeling much better today (went back to work). I'm hoping another 48hrs of taking it easy, I'll be able to get back out there. My bigger obstacle this weekend will be I have a bunch of family coming into town for my son's Dedication at church this weekend.
I will post an update and pics as soon as I can, though.

[Gerziebaker]

The reason that I was wondering is that mine just did the same thing. I going to check mine this weekend. I'll let you know what I find.

[RoninLB]

[danielt]

Well, I got the cam covers off this weekend and here is how the tensioners looked:




So next I checked the cam timing. Get everything setup on TDC on cylinder #1, rotate 360 degrees, no movment. As I go just past TDC again, valve starts to lower. Cam timing was originally set at 1.0mm(0.040inches). To get the same reading I have to rotate the crank to here:

So left bank timing is off quite a bit, but I don't understand why...

Will check the right bank next.