o2 box problems

[j8tg]

I have been chasing a rich on boost condition for about a year and the mechanic has isolated it to a bad duty cycle on the bosch sensor'(pt # 930.617.103.00). So far I have had a rebuilder send two boxes up that didn't work. The problem is resolved when we switch boxes with a customer car in for service.

Can anyone point me towards an available box or someone who can repair mine?

Thanks,

Tom G.
1986 930

[9dreizig]

I can't help but wonder if it will go away when the o2 unit is unplugged?

[j8tg]

The tech tried that, as well as attempting to bypass the entire unit without success. He has also replaced the wur and the cold start valve-----runs great until it hits boost then pukes fuel through the exhaust, mild at Denver altitude but it can't be driven at anything over 7000 ft.

[mark houghton]

You should be able to unplug the O2 sensor, then re-adjust the idle mixture via the screw on top of the fuel head to something close to 3% CO and just run without it forever. Very simple. If your "tech guy" did just that and it still won't run properly on boost, it still reeks of a bad WUR or a serious air leak (where some of the already metered boosted air would escape, causing a rich condition). But with such a leak, you may also experience a lean condition at idle and rough running...depending on the size of the leak. CIS is a weird thing. WUR system and control pressures check out ok?

But you did say that it works just fine with somebody else's box installed (did your guy do the O2 delete with the borrowed box, or with your suspected bad one)?

Something isn't ringing true here. If you haven't pulled the intercooler, turbo up-pipe, and associated hoses lately to check seal integrity, then it certainly can't hurt.

Don't feel alone...I've been puting off checking my seals to fix a weird problem that occurs only after a hot shutdown and sits for a couple of hours, restarting and and finding that my AFR's go pig-rich at mellow non-boost throttle beyond about 3200 rpm's. Minimal non-measurable boost onset, air leaking past an O'ring most likely, going rich. Stone cold starting in the morning and I can run all day with no problems until I shut her down and everything gets heat soaked.

[j8tg]

He replaced the wur without any improvement so switched back to the original. Pressures all check out fine. Good question on which box the o2 disconnect was tried on, cold start and idle both cold and warm are spot on. Inter-cooler o rings were checked.

The whole issue reared its head at the same time the car was repeatedly failing emissions and adjustments were being made to compensate for the lack of a cat converter.

One year later and about $2000 lighter the fight is still on--getting a bit discouraged.

[9dreizig]

One thing to try is while under idle, spray around with carb cleaner,, if there's a rise in rpm you've got a leak.. that's where my money is betting.

[scmguru]

Is the frequency valve working? I had a problem where the ECU was actually disconnected at the fuse block in the engine compartment.

I ruled out vacuum leaks, incorrect WUR pressures, O2 sensor issues and after about 6 weeks (and 2 P-Car specialists) of effort, determined the ECU wasn't 'on', therefore the frequency valve wasn't working and the O2 sensor output was irrelevant.

[mark houghton]

Originally Posted by scmguru

Is the frequency valve working? I had a problem where the ECU was actually disconnected at the fuse block in the engine compartment.

I ruled out vacuum leaks, incorrect WUR pressures, O2 sensor issues and after about 6 weeks (and 2 P-Car specialists) of effort, determined the ECU wasn't 'on', therefore the frequency valve wasn't working and the O2 sensor output was irrelevant.

IF the frequency valve isn't working (i.e., not energized) the engine will run extremely lean. That valve makes a noisy buzzing sound and you can hear it run by forcing the fuel pumps on by pulling the blue switch connector that's connected to the contol arm at the top of the fuel head.

I did that just for kicks a couple weeks ago, to see if I could tune the car without the freq valve operating continuously. Very lean mixture resulted, which couldn't be tuned around.

[j8tg]

The frequency valve was also replaced. Good idea on spraying carb cleaner to find a vacuum leak---where would the key areas be to spray?

Thanks,

TG