Idle and AFR issues
 

I am having issues that have not been able to troubleshoot or find info by the means of searches.

My turbo 3.6 has a hunting idle, the AFRs seem inconsistent (with the Oxygen Sensor Disconnected), and on high free reving the car will stumble. I do have a LWFW but this should not be an issue.

I was thinking accumulator but the condition is the same hot or cold. The other possibility could be the WUR?

I am kind of scared of going the fix the CIS path and end up spending 1K+. Might as well skip this whole process and go straight to EFI. I really do not know what to do.

I am kind of venting.

What the hell is an LWFW? I thought I had all the acronyms committed to memory, but it's late in the day and I'm tired already.

What are your AFR's reading at idle, etc. Hunting at idle is usually an easy fix with adjusting the mixture, but if you're also seeing a stumble at high rpms then something else is amiss. Need more info on what your AFR's are doing...your term "amiss" doesn't tell me squat. Did this just happen out of the blue one day, or has it always been there and getting progressively worse (you know, like you were blasting down the road one day on full boost in all 4 gears, burning rubber and just running like a bat outa hell, and afterwards the symptoms occured)?

Start with the simple stuff first, like plumbing. You may have an air or vacuum leak. Are other aspects of tuning spot-on (timing, cap, rotor, plugs and wires good, etc.). Stumbles and hunting usually are fuel mixture related, and with CIS there are several things that can mess with your mind.

Don't give up until you give up, 'cause EFI will cost you a boat load more than what is probably a simple fix on the CIS. CIS is dependable....when it wants to be. And when not, it can drive you to drink.

LWFW = Light Weight Fly Wheel?

Ahhhhh.....In the words of the great Grey Poupon commercials - "But of course".

I need to add that to the list of acronyms I started awhile back.


YouTube - Grey Poupon Original Commercial

Correct A930Rocket.

Mark, my car went to the mechanic for clutch replacement and in the process we put a light weight flywheel among other things. My mechanic found two of the plastic manifold spacers cracked. He replaced all and cleaned the injectors. Along with the job we decided to remove all the smog stuff. All vaccum lines were replaced, new ignition rotor, the cap, sparkplugs, filters, aluminum BOV, valves adjusted.

Before the above job, the car never had a hunting idle and would not stumble when reving the engine while stopped.

After the job was performed my mechanic told me of the hunting idle and that he had to raise the idle because the engine would stumble off.

Immediately I realized on my Zeitronix display the fluctuations on AFRs from 12.8 to 13.8. Also realized the car running overly rich making the car to hesitate underload at partial throttle and some black smoke on full throttle.

I leaned out the mixture fluctuating from 14.2 to 15.1 and I was still hitting the 9s on midrange boost and never more than 11.8 at peak rpm at WOT third gear. All in all, at this point no issues with engine not idling/dying at low RPM.

I used it for three consecutive week-ends.

So when did it start happening? Yesterday went on another group outing as the others and as always I hit the occasionaly 145mph+ and do a lot of 3rd and 4th gear pulls. So I did drive the car hard but not any different from my usual driving. On this day I realized that when I got to the toll booths the engine would die. Then on the highway I did a couple of tests pressing the cluch and watch the engine rpm drop and the engine die.

Got home and played with the mixture and got the car to idle again. Went out for a test and same idle drop issue again. I can't find any consistency that may aid the troubleshooting.

Any help appreciated.

This appears to be a sign of too rich a fuel mixture. Hunting at idle happens when the mixture is rich. At idle, I see hunting when AFR is in the 12 range. When AFR's dip below 10, at higher rpms the engine can bog down.

If the spacers were cracked and produced vacuum leaks, then fixing it would create a rich mixture.

My first thought would be to look for a dislodged O'ring at the intercooler. It may have be been leaking and about to go earlier, then after your last hard run it probably tore and the boost blew it out of place. Had that happen to me once; the car would not idle and would stumble and run pig rich with about half the power it should when on full throttle and building boost. If indeed you did have a leak earlier and attempted to adjust with the mixture screw, then of course you'll find your mixture wrong once you fix the leak.

Pull the IC, take a look....it can't hurt and doesn't take much effort. Look especially at the O'rings from the up-pipe from the turbo, most common failure point. Also make sure that all IC and turbo mounting points are secure so everything stays lined up properly and doesn't move when the engine torques.

Thanks Mark, I actually took the IC out, checked the orange ring and all the other connections (AAV, BOV, turbo neck, and vacuum lines under the intercooler) plus the two fuel pumps and all looks normal and still having the problem.

I am scratching my head on this one, as I am writing this, I thought maybe the BOV (although it is an aluminum one) is getting stuck open. Currently I am at work, so that test will have to wait but it is highly unlikely. I will do a re-inspection of IC/turbo/vacuum connections and if this fails I fear it could be the WUR gone "loco".

BTW, I don't think I have O-rings on the up-pipe from the turbo, my car is a C2 turbo, it uses the goose neck hose. Am I correct, or are you referring to something I am not aware of?

One question, I just said my orange O-ring is in place, but I have to ask, the IC goes on fairly smooth, almost no effort and it has always been this way, could it be a worn O-ring letting air leak around it or is this normal. Gonna have to get the Carb cleaner out again....

I keep getting bit by the C2 thing lately (of which I'm not familiar). Thought we were dealing with a 930. Sounds like you've checked and confirmed all the obvious stuff. Do you have the gauge setup to check control and system pressures on your WUR, or know of some kind soul that would let you borrow a known good one? Gotta take that possibility out of the equatin, one thing at a tine.
The only other thing I can think of would be to do the "squirt flammable sfuff all over the place" test, to look for vacuum/air leaks.

Well, I explained the conditions to my mechanic and he insists it is the WUR without putting any pressure gauges, thinking about sending my WUR for refurbishing and making adjustable.

CIS control pressure gauge is one single pressure gauge with a ball valve in the hose after the gauge that is hooked up in series in the control pressure line .

nobody can diagnose K jetronic fuel injection without it, you or they can only make educated guesses that may be wrong.

the inlet fitting on the CIS control presure gauge and hose set will also screw onto the fuel line going to the 930 rear fuel pump so with it attached and the ball valve closed you can check the fuel pressure from the front pump with it.

Troubleshooting 101: Ask "what has changed?"
Your mechanic stripped off the smog stuff. How much? Be more specific. Did he remove something he thought was unnecessary or irrelevant, but wasn't? Are all the myriad vacuum lines correctly routed (and how are you verifying? Workshop manual diagram?)

We have seen some aluminum BOVs that are open at idle, and some that leak. That's worth checking.

1. Check WUR fuel pressure.
2. Lean under boost can be a boost leak. Fortunately there's not much between the turbocharger and your injector blocks: gray charge hose, intercooler's fittings, o-ring above & below throttle body, a few manifold fittings, and injector blocks and gaskets.
If you or your mechanic have access to a diagnostic smoke machine, that's extremely helpful for finding leaks: fill the system with smoke, pressurize it up to a few psi.
FWIW, I find vacuum leak testing with propane is helpful, too; easier on the O2 sensor and paint than carb cleaner.

It's possible for the WUR to have failed, but spontaneous failure of the WUR while the engine is out and apart... I would be skeptical.

I'll be the first to admit that the learning never stops with these cars, but my understanding with CIS systems is quite the opposite. Air leaks under boost cause rich conditions. Since the fuel flow rate to the injectors has already been set by the amount of air moving across and deflecting the metering arm attached to the fuel distributor, any volume of that pressurized air that is allowed to escape after that point and before reaching the cylinders will result in a rich conditon.
Now, that's CIS and please correct me if I'm wrong but....does the C2 use CIS or EFI? Probalby EFI, in which case....NEVER MIND my comments!:)

I sit corrected. Typed that backwards.
Boost leak = pressurized air, that is already been metered and a commensurate amount of fuel delivered. That air leaks out before making it into the cylinders, and the engine is rich.
(Careful typing tech advise when bleary tired.)

Been there done that more than I care to admit. Good that we're all on the same page.

Internet diagnosis is a dangerous thing but I can give some observations.
- Car ran fine originally.
- Mechanic removed and changed CIS / smog equipment, ran bad.
- You tuned mixture ran good.
- Ran car hard now runs bad again.
It seams logical that the tuning you did after the CIS equipment was disturbed compensated for that disturbance. It could now be that once the engine went through a long hot cycle the disturbed items have become loose and are leaking metered air.
Have the phenolic blocks been re-tightened?
Was the EZ69 checked out and functioning properly?
The -164 WUR on the C2T is much more complicated that any of the 930 WUR's. If signals to any of the vac ports were disturbed during the CIS/smog trimming there may be imbalances and quirkiness resulting; something to check. When we modify one of these cars both the fuel head and WUR are swapped out for modified 930 units and all the electronics defeated. Result is a simple system like the early 930.

what's the chance that you're getting a bad electrical connection at the WUR? Thus, causing the 'engine heat' alone to heat the WUR element... thus, causing the WUR to intermit between cold and warm pressure settings...

maybe try swapping the WUR connector with the AAV connector [or, AAR - whatever it's called].

Don't know if you're car had one of those...

As said by Brian , it is really not easy to give advice through internet .


You mention trouble at idle and under partial throttle.


You should verify the throttle 3 position switch . This switch is known to failed with time. It can fool the Kjectronic enrichment function as well as the EZ69.


Just a 2 cents idea....


;):)

I apologize for my disappearance after all the dedicated input here. I was putting long hours at work. Anyways, I will go through all troubleshooting recommendations and report back. If it turns out to be the WUR I am leaning to just go straight to EFI.

Well, started troubleshooting and have targeted the area of the problem among other questionable things.

Started by spraying carb cleaner all over the manifold area and nothing.

Disassembled the BOV and saw that it might be missing an O-ring. I assembled it and I can blow through it although barely. Still, swapped with the old Bosch unit which I could not blow air through. No changes to behavior anyways.

Checked the AAV again by clamping the hose going to the IC and no change in idle. Still, decided to remove the hose going to the IC and indeed, the AAV is leaking air but I am not sure if it is normal for it to leak some air since it is completely mechanical and the little door closing I don't think is leak proof. I put my thumb on the hose going to the AAV and can feel the suction. In order to eliminate this as the culprit, I proceeded to put temporary caps on the IC and the AAV and again, no change in behavior. Could someone put your thumb on your AAV an see if you can feel a normal suction on it when it is supposed to be shut?

So in my frustration I started bathing all possible areas with the Carb cleaner, I know it is not the best thing but remember that by then I had inhaled lots of carbon dioxide and unburned fuel. FOUND THE LEAK OR VACUMM!! (Excuse my screaming), I sprayed the turbo to IC neck until it would drip down and voilá, car quits. So must be one of the connections to the turbo (Air intake or compressor output) or the thick hose that runs close to the two.

I am letting the car cool down so I can get my hands in there. I guess I may have no excuse to move to EFI at the moment.

Thanks again for all the input and I will post back the final diagnosis/solution.

BTW - Thanks to one of the vendors who made me a very kind offer to send me a 3.6 WUR free of charge for testing. I would mention the name but I am not sure if I can or should. When EFI time comes, I will be giving them a call.

Ok, car cooled down, started inspection and found out the problem was the goose neck IC hose was cracked at the turbo end. I cut the bad part, about 1/4 of an inch, and put it back on. Problem solved. Car is much faster and it can transition like it should. I had to adjust the mixture towards the lean side about a full turn, that's how much the mixture was compensating for the leak.

I did another carb test and all perfect in the turbo area, but, I sprayed around the throttle body and the idle changed a little, so I have a minute leak somewhere there and I think it is a worn orange O-ring. That said, I will take care of it but the car is back to normal.

I always thought that the mix control screw had 1/2 of a turn range... slight turn should make significant differenc on the CO level... but regardless, glad the car is back to normal.

Excellent excellent excellent! So glad the "squirt and find" worked for you! I just love doing these internet diagnoses....they seem to cycle from the simple - to the extreme - to the downright scarey OMG it will never run right again - back to the simple. Glad in your instance it was simple. Now go out and rod the hell out of her!!!