6.9 Stumbles when reved

[Mr6.9]

Back to work on the fleet of 6.9s after acouple cold months. My last post was about oil circulation issues. That issue resolved itself and tank refilled with oil. Now onto the stumble. Engine starts and dies after about 5-10 seconds after a couple attempts it stays runnings. I let it warm up. I go to check if its at all responsive, just slumbles. If i feather the gas its more responsive. If i just press the gas it comes real close to stalling and sometimes backfires out the intake. Smells a tad rich, not real bad though. Any thoughts?

[daantjie]

First start with vacuum leaks. Triple check all vacuum hoses and rubber connectors. Any vacuum leak will cause runability issues.

[rumb]

There are so many components in this system, you need to work thru them and verify they work correctly.

I would start with the AAV.  When the car is running is your throttle speed air adjustment screw turned all the way in? if so your AAV is not working and needs cleaned up.  several posts on how to do this easily. When you start the car is the idle higher and then drops after about 3 minutes?

Second I would check ignition timing.

Then I would adjust the fuel screw just in front of the fuel disti, be very careful here, make small adjustments only.  mark your original spot. Make sure the access hole is plugged shut or at least put some duct tape over it when you are done adjusting. If you dont, then a lot of air will be sucked in the hole.

[UTn_boy]

Rumb, a lot of the CIS engines don't have this mixture adjusting screw.  It can certainly be added, but isn't really necessary if all is well, and the air plate is properly positioned.

Mr6.9, Rumb and Daantjie are spot on.  There usually isn't one thing that causes your problem, and there is no magic screw you can turn.  If you're mechanically minded, then buy a book, pressure gauge test set, and a vacuum gauge.  Follow the procedure to test the upper and lower chamber pressures, and note the pressure differential when hot and when cold.   

One other area I recommend having a close look at is your fuel tank.  You mentioned these cars sat for several years. Make sure the tank is clean on the inside, and that your filter isn't clogged up because of a dirty tank. 

[Mr6.9]

UTn_boy is correct. There's no  mixture adjusting screw. But I don't think the issue is injection system. At least not the main issue. I believe it's a bad gasket. Possibly one of the injector o-rings I installed. Looked at the tailpipe. One side dry the other side is wet. Also hooked up my vacuum gauge. When I first get it running, gauge reads 8-9" of vacuum. After running about 10 minutes, it's at about 12-13" of vacuum.

[UTn_boy]

You should be at 15-17 in HG after warmed up. 

[Randys01]

Assuming you have got 8 good consistent sparks, I would be suspicious of 1, 2 or 3 partially clogged fuel line circuits; which includes injectors.
This is not easy to diagnose so before tackling this, make absolutely certain your delivered spark is spot on. I had this problem  for 18 mths and every genius in town had a crack at it. It was just by chance I discovered the wrong rotor button had been fitted and as it swung past no7, she didn't make contact coz it had the wobbles at a certain speed.

[Mr6.9]

Assuming you have got 8 good consistent sparks, I would be suspicious of 1, 2 or 3 partially clogged fuel line circuits; which includes injectors.
This is not easy to diagnose so before tackling this, make absolutely certain your delivered spark is spot on. I had this problem  for 18 mths and every genius in town had a crack at it. It was just by chance I discovered the wrong rotor button had been fitted and as it swung past no7, she didn't make contact coz it had the wobbles at a certain speed.

I really hope its not the fuel system. So far in the last 8 months, i've cleaned the injectors, installed new orings, replaced the fuel filter,  purged any stale gas out, and rebuilt the fuel distributor. Did notice one of the ballast resistors are cracked but doubt that would allow the engine to run better as it warmed up. New ballast resistors have already been ordered in case your wondering.

[rumb]

Have you had your WUR checked out?  and what about the questions I asked concerning the AAV and idle screw. Is the idle screw screwed all the way in?

[Randys01]

Can we assume you have the kit and familiar with  the basic CIS pressure test regime which have all checked out A1 OK?
Yes?.  Continue
NO?.    Go no further until you have done this.

[Mr6.9]

Have you had your WUR checked out?  and what about the questions I asked concerning the AAV and idle screw. Is the idle screw screwed all the way in?

haven't checked the WUR yet. I need to find the correct fittings for the fuel pressure tester. Also have to figure why the gauge on my harbor freight tester won't release pressure till it's unhooked. Haven't checked the AAV yet. Got my fingers crossed hoping none of the tubes break when I remove it. The idle screw is not adjustable. It's just a stop screw.

[Mr6.9]

Can we assume you have the kit and familiar with  the basic CIS pressure test regime which have all checked out A1 OK?
Yes?.  Continue
NO?.    Go no further until you have done this.

haven't not done that yet. I have a crappy fuel pressure tester from harbor freight. It doesn't have the correct  fittings to hook up to the WUR. Only been able to hook to the main fuel line. Made nearly 100 psi, but the guage isn't releasing pressure properly. Thinking there's an issue with the shradder valve.

[Randys01]

You can't expect to sort out one of the most complex cars ever made, now 40 years old, with test equipment that is dodgey and not fit for purpose.
The Bosch CIS has a 1000 moments of truth after this age and can only be sorted out with a systematic test regime. Hoping to snag a fix is the road to despair.
This is not a simple little  Austin A40: which is why 40% of 6.9's have been left to rot in junkyards and paddocks. Simply too hard to diagnose and too dear to fix!

So please start afresh.

Get a decent CIS test kit and sort out the first principals.  ie fuel flow & volume..system pressure..cold and hot control pressures etc etc. You need to be dead set certain these are all in- range before embarking on any other crusade.
Trust me....I've been around the world 5 times on this thorny topic ,culminating in building my own test rig. Amazing the home truths this throws up and illustrates how fragile the relationship is between all the components if you want it running properly.

Of course, it could be worse...it could be D jetronic

[rumb]

/quote]

Look at the HF website for the preasure tester and read the reviews.  there is an issue with the schrader valve and someone explains how to fix it.

Their website is down temp for maintenance so I cant look right now.


http://forums.pelicanparts.com/porsche-911-technical-forum/838021-harbor-freight-cis-fuel-pressure-tester-review.html

[Mr6.9]

/quote]

Look at the HF website for the preasure tester and read the reviews.  there is an issue with the schrader valve and someone explains how to fix it.

Their website is down temp for maintenance so I cant look right now.

http://forums.pelicanparts.com/porsche-911-technical-forum/838021-harbor-freight-cis-fuel-pressure-tester-review.html

I'll check the website. I remember others having issues with the schrader valves, but thought it was a issue related to flow. Already found a couple issues. Pulled 4 of the injectors yesterday. Since the left tailpipe was wet i assumed weak or stuck open injectors. Installed on my pop tester today and the spray patern is terrible on 3 of them. 2nd issue: It appears as though i have the wrong injectors. Injectors read 0 437 502 010. The other injectors ive pulled out of the parts car read 0 437 502 047. Auto parts stores gave the same number. Wondering if this is the reason why opening pressures were off. Originally thought i just had a inaccurate pressure gauge