another strange behaviour - '86 930

[albinski]

hi Pelicans,
the saga of getting my emission control system working properly continues ...
after solving the issue with AFR going pig reach on idle (addn'l grounding added to the brain), now during test drives it appeared that when cruising at ~2500rpm, it feels like the car is slightly getting held by something. It is really hard to explain that, but again it is not cruising smoothly.
i appreciate the description above is poor (to say the least) but hope it gives a clue of what we are trying to fight with here

perhaps worth adding is the fact that if oxy sensor gets disconnected, the issue disappears and car cruises flawlessly so clearly there's an issue with the way emission control system works...

a pic of my beauty below

[Roby466]

could it be timing? I had a similar with the SC I had before the 930. It had been setup by the shop with the Ox sensor disconnected and when I plugged it in the distributor issues started showing up. I ended up needing a new distributor and re-timed myself as per spec and all was perfect.
I think some perhaps disconnect the Ox sensor and run a bit rich with more advance and it masks other small issues... but it's not quite right.

[Jeff NJ]

Do you have an AFR gauge hooked up? Your description kind of sounds like what mine felt like when it was too lean.

[bpu699]

My car went pig rich randomly too. Search my threads from years ago. I also found it to a ground. But it wasn't perfect. Put in the msd ignition and problems went way...

These cars are fun, eh?

Which part of Poland you in? My parents were from gronkowa...

Bogdan

[T77911S]

how old is the O2 sensor
you could still have computer problem.
when you disconnect the O2 it goes open loop mode, also goes open loop about 3500.
when it does this the frequency valve goes to a set freq and AFR is basically set based on the CP setting and the mixture setting.
in closed loop AFR is still based on those settings BUT the AFR is adjusted by changing the duty cycle of the freq valve.
there is also a throttle switch that tells the computer when It is idling and WOT.

you really need to see what the AFR's are doing at idle, 3k rpm and WOT.
I would also check the FV. check to see if it is working and the duty cycle.

if nothing else, get it running good without the O2. set the mixture to spec, connect the O2.
if you still have an issue then look at the electronics.

[albinski]

Thanks for all the answers.
@Roby466 - your suggestion re timing is hard to reconcile given the fact it drives fabulous without ox sensor connected. don't wanna go easy here and just ride with ox disconnected.still trying to fight the beast.

@Jeff NJ - no, don't have AFR hooked up. looking to put sensor to the muffler and see what comes up on the dial.

@Bogdan - fun seems like an underestimated word i am from Bydgoszcz:https://www.google.pl/maps/place/Bydgoszcz/@53.125811,17.898098,11z/data=!3m1!4b1!4m5!3m4!1s0x47031386764ebd6f:0xe49ee 48c4b65f30e!8m2!3d53.1234804!4d18.0084378

@T77911S - o2 sensor is new. it was a first thing that got replaced when observed issues with ox system.

AFR at idle, w/o sensor connected is set to high 12's. have not checked yet what is the reading at 2.5-3k nor WOT.

as for FV - it does vibrate when ignition is on, so it works (not sure if it works properly, though!). any way i can test it? how do i measure its duty cycle?

thanks again all!

rgds
Krzysztof

[Roby466]

Understood. I agree it doesn't seem to make sense. Mine was going well with ox disconnected running slightly rich but timing seems to affect afr and drivability depending on how rich you run.
I would first set timing as per spec, (I think it calls for vacuum lines to dizzy disconnected and plugged) check the system pressures and if all ok, set idle mixture with ox disconnected by reading voltage on ox. (As you don't have AFR) Then plug everything back in and see how it goes.

[tasturbo86]

My '86 ran poorly with an old O2 sensor.
Maybe try another one just in case the new one is bad?
Check the distributor advance mechanism. After 30 years it may may be sticking.
Fuel pumps ok? You have 2 of them.
Fuel filter ok?
Yell if I can check anything on mine.
They are wonderful cars. Don't even think about selling it. (Unless you sell it to me)

[T77911S]

what are your CP's

you really need to know what the AFR is doing at 2500.
if you cant do it driving check it parked at 2500.

you can try disconnecting the O2, set the mixture to spec, then reconnect the O2.
if still bad you may have some bad electronics under the seat.
start with the O2 sensor relay. make sure the O2 is getting power.

[albinski]

Again folks - thanks for all valuable advices.
Afr measurements - all done:
Idle w/o oxy - 12.3
Idle w/ oxy - 14.7

2500rpm while driving/cruising - 14.5 with oxy, 13.3 w/o oxy

So seems oxy is clearly pulling the mix towards stochiometric no at all rpms.

Distributor has been completely taken apart, cleaned, lubed abnd put back together. Looks like new inside-out.

Freq valve vibrates.

Two new oxy sensors have been in the car -both work the same.

Oxy gets 12v, that has been checked too...

All the leads gived here have been pretty much checked and no progress made by even an inch...

I am close to take a pass for now, pull out the plug and just enjoy driving.
Perhaps will come back to it sometimes later with fresh mind

[mark houghton]

Unless you're a glutton for punishment and just absolutely must have everything original, then unplug the damn O2 sensor and tune around it. It's not needed and makes a world of difference without it ... unless you are forced in to emissions testing to get licensed.

[billjam]

I was about to suggest the same thing as Mark. If you can do it without incurring any licensing problems, just yank all that crap out of there.

My wiring diagram here shows all the devices and wiring that can be safely removed.

[flightlead404]

I bet its a bad ground or relay somewhere, but who cares, disable it like the others say.

[T77911S]

he has to leave the FV and the controls for it unless he gets the fuel head modified to run without the FV.

[T77911S]

he has to leave the FV and the controls for it unless he gets the fuel head modified to run without the FV.

[mark houghton]

Originally Posted by T77911S

he has to leave the FV and the controls for it unless he gets the fuel head modified to run without the FV.

True. All that I offered was to unplug the sensor and tune around it, not affecting the hornets nest freq valve from buzzing its heart out.