2.7 CIS Only Running on left cylinder bank

brksb46041 · 10-13-2009, 01:44 AM

Hi, its been a long time since i've posted, have been very busy with work and school. I bought this car non-running and it had been sitting for about 20 years in a garage.

I finally got the MSD CDI box and coil hooked up. At first it didn't have a spark but after filing a little material off the points they are making contact and produce an excellent spark. It will start right up but it will die shortly after. I can tell that it is definitely not firing on all cylinders.

There is spark on all cylinders, and there is good compression on all cylinders. I have checked and there is power going to the cold start valve when the engine is cranked. It is not starving for fuel, i pulled an injector and let it run while letting it spray. The spray pattern was not the best at higher fuel settings (pushing on the flapper valve) but it seems good enough to run.

I pulled the spark plugs one by one trying to see which cylinders were missing but i couldn't reliably tell which one affected the running. I eventually pulled an injector (on the right bank, which wasn't firing) and sprayed it back into the intake while feathering the flapper valve and got it to stay running for about 90 seconds so that i could feel each header to tell if it was running. The whole right bank was cold and not firing. There was also fuel in the exhaust of the right bank after this. I later pulled a plug and it was dry though,,,

Any ideas on what would cause it to only run on the left bank? After reinstalling the distributor i lined upthe Z1 mark on the crank and pointed the rotor towards the #1 plug wire on the cap. Can these be timed 360 degreees off? I rotated the distributor 180 degrees to check and got backfiring through the airbox,,,,

This may be unrelated, but i noticed the throttle valve doesn't fully open, there is still about 20 degrees of rotation to go after it reaches the stop. Also, there is no microswitch (as described in the manual) that the throttle lever pushes against.

Thanks in advance for any help

Walter_Middie · Walter_Middie's Garage

We need to know what year the 2.7 is from as there are small differences in the CIS from year to year.

You didn't mention cleaning out the gas tank - are you using fresh gas? After 20 years, the gas in the tank will be too old to run.

T77911S · 10-13-2009, 05:36 AM

with the key on and engine off, raise the sensor plate and check resistance as soon as you lift it. there sould not be any play.

MURF · 10-13-2009, 06:12 AM

what type of spark plugs?if using bosch platnums [the cheap ones] replace with ngk's..fixed similar problem

gsmith660 · 10-13-2009, 06:57 AM

Got any noise coming from the chain housing on the side not running I had the nut come off the cam and release the cam sprocket and cause no cam movement on 1 bank hence that bank was dead gas poured out of the intake when I turned the motor over

Grady Clay · 10-13-2009, 07:29 AM

STOP.

If a 911 engine is only running on one bank, it is critically important to confirm that the cams are in time. While the problem may be with fuel or ignition, jumped cam timing can lead to major destruction in the engine.

To check, simply remove the intake valve covers, check that you have valve clearance on #1 & #4 intake valves and check the cam timing. If off, it will be WAY off. No subtle measurements here.

If the timing has jumped, further running can cause great damage. Search on my name and cam timing damage to these engines. We had one at the extreme. The owner quit driving (sorta) when a wrist pin broke a fan blade and wedged against the crank pulley.

Best,
Grady

brksb46041 · 10-13-2009, 11:39 AM

Thanks for the quick replies! The engine is a 74. There is zero play in the sensor plate and it is fresh gas with a new accumulator and filter. I can't hear any abnormal noises coming from the cam chain housing, and there is compression on that bank,,,

I will swap the plugs between the banks today and take the intake valve covers off to check timing.

dtw · 12:36 PM

Grady's advice is to be heeded, as anything is possible. The more likely scenario involves a plugged-up fuel system, though. All the injectors should be cleaned and pattern-checked. When resurrecting CIS systems, I have had about a 50% success rate with several dozens of injectors over the years. The fuel head could also be plugged up.

First thing I'd do, if it were me (and you don't have to turn the engine over to do it), is to put each injector into a separate flask, then lift the sensor plate. If you want to get super-fancy, there's even a liters/minute spec in the book somewhere. Still, this test would at least tell you which injectors (or ports on the fuel head) are weak. Obviously, any injectors showing weak should then be swapped to the position of a strong injector, to see where the problem lies (is the injector really weak or is the fuel distributor giving a weak supply to that particular line).

Any good local Euro service shop that works on BMW, Mercedes, Porsche, Audi, Ferrari, VW, etc. should have an injector spray checker. This is much safer to use than individually spray-pattern testing your injectors on the engine. Even if you are getting good flow from an injector, that doesn't mean you are out of the woods. Even after doing the tests above, you must still pattern-test the injectors. If they are sticking open, sticking shut, dribbling, or spraying a stream of fuel, the injector is bad (or needs a further attempt at cleaning, depending on how much your time is worth to you).

The injector must fire a nice fine mist of fuel if the CIS-fed cylinder is to have any chance of lighting off. If it gets a delivery of liquid fuel, the cylinder will just get washed and never fire. We had a case of this where a 4-cylinder VW engine would take forever to start and ran like crap at idle/low load. When at WOT, it ran like a champ, though - that's the only time all four injectors were firing properly. At low load, two injectors were dribbling liquid fuel that the engine couldn't light off.

After you know your injectors are all firing properly, and that your fuel head is not plugged up, you have to check vacuum. Common injection air leaks on an old, dried-out CIS 911 are: injector o-rings, injector mounting block and/or seal, intake manifold boots (upper) and gaskets (lower), and then all the various vacuum hoses and hardlines.

On the last CIS engine I resurrected - '76 911 asleep for 20 years - I just pulled the entire fuel injection assembly and went through everything. It was a lot easier than trying to troubleshoot everything piece-meal.

brksb46041 · 10-13-2009, 07:45 PM

Quote:

If they are sticking open, sticking shut, dribbling, or spraying a stream of fuel, the injector is bad (or needs a further attempt at cleaning, depending on how much your time is worth to you).

Well this is good news, my time isn't worth anything to me!

Any tips on disassembling an injector to clean the tip?

dtw · 10-13-2009, 08:18 PM

Quote:

Originally Posted by brksb46041

Well this is good news, my time isn't worth anything to me!

Any tips on disassembling an injector to clean the tip?

To my knowledge, CIS injectors are not serviceable. You can ultrasonically clean them, or spray solvent through them (using the injector test rig, not just a can of Brakleen...you'll just make a mess and waste money doing that), or both, until you can't take it anymore.

Sometime the injector 'comes back', and sometimes it doesn't. My experience has been, that if they're going to come back, they do it pretty early on - extended diddling usually doesn't bear much fruit.

Eagledriver · 10-14-2009, 06:21 PM

Do you know if the engine ran successfully 20 years ago? If it was rebuilt it's possible that one cam was installed 180 degrees out. To check you need to see that the intake valve on number 1 and number 4 open 360 degrees apart and not at the same time.

-Andy

brksb46041 · 10-17-2009, 10:12 PM

Update: I had one injector that wasn't spraying so i cleaned it up and got it spraying good. After a few tries it fired and stayed running for about 15 seconds and it ran very smooth. It sounded like it was running on all 6 cylinders but after it died i felt the exhaust and the right cylinder bank was cold. I tried starting it again but this time it wouldn't start at all, though it was firing a little. It also backfired and my friend said he thought he saw the flame below the airbox,,,,

I took the valve covers off and at TDC there is about .002-.003" of play in the #1 intake rocker and the #4 intake rocker has zero play (it is just starting to open). This contradicts what grady clay said above (i think) but seems to be correct according to some other threads i was reading. Can anyone confirm this (or can you elaborate grady)?

Lastly, i have been reading some other threads regarding the fuel pump and relays and i think that my fuel pump relay may have been bypassed. When i turn the ignition on, i can hear the fuel pump in the tank running. Is this normal? The wiring is sort of a mess on this car,,,, The injectors spray fine when the plate is lifted,,,,,

Thanks again for all the help, I have experience working on lots of other cars, trucks, and bikes but this 911 is a whole new can of worms. I am completely lost on this thing.

brksb46041 · 10-17-2009, 10:45 PM

Also, this airbox has no pop off valve. When the airboxes blow, where do they break? Is it easy to tell?

w21055 · w21055's Garage

Quote:

Originally Posted by brksb46041

Also, this airbox has no pop off valve. When the airboxes blow, where do they break? Is it easy to tell?

The only one I have seen blown blew at the seams where the top and bottom came together. You could tell with it off, but I don't think you could have noticed it on the engine.

dtw · 10-18-2009, 05:57 AM

Oftentimes, if they start then die, it is a vacuum issue. The car starts on the cold start injector and runs for a few seconds. Then the lack of vacuum fails to lift the sensor plate, and the car dies. Time to sort out vacuum...

gsmith660 · 10-18-2009, 06:13 AM

You said the exhaust was cold on the right side after running for 15 sec. did you check each exhaust or at the collector? So whats common to that side and nothing else? I would not think a vacuum leak would make 3 cyl. on 1 side not fire. Have you looked at the rubber sleeves that connect the airbox to the runners on the right side? Are they intact and connected?

Walter_Middie · Walter_Middie's Garage

Quote:

When i turn the ignition on, i can hear the fuel pump in the tank running. Is this normal?

Yes, this is normal for an early CIS. When the ignition is turned on, the fuel pump runs, and the fuel is pumped in a continuous loop using a return line from the fuel distributor to the tank.

I don't think you have a fuel pump relay.

brksb46041 · 10-18-2009, 11:20 AM

If I get a chance to tinker with it today i will check the intake boots and report back.

I have tried manually raising the plate while someone else starts it but this has little effect.

Also, i checked the exhaust at the cylinder after it was ran.

Does anyone have a picture of a blown airbox? Also, i am thinking that maybe a mouse got up in there and plugged the exhaust on the right side, i am going to try removing the exhaust later to check.

Thanks again

gsmith660 · 10-18-2009, 12:12 PM

When I started my motor after installing the turbo I blew a mouse nest out of the muffler and the rest of it burned out over about a hours time.

Tooth911 · 10-18-2009, 12:55 PM

Blown air box will show separation at the mid seem as mentioned.Ive been through lots of cis grief with my 77 911.If a backfire has happened through the air box and caused it to split the car will not run.Take a picture of it and post it.also do a search here on cis and blown air box.Also a bently manual is a must.Cheers Chuck