Hesitation and black smoke when boosting

[Motte]

Hi all,
Have an issue when car is on boost that I hope someone can help me diagnosing.
I recently installed a mint Andial short neck IC and removed all the smog equip from my 86 930/68.
Now I experience hesitation and black smoke when on boost around 3000 rpm. Its not a hard face in the dash cut off, but hesitation and especially in 3-4 gear.
All other is stock except a Rarlyl8 Hooligan muffler installed a while ago (with no issues except dramatic change in power and sound - awesome).
I already reinstalled and retighthen the IC and checked the o-rings and bands.
At the same time I replaced the O2 lambda sensor, just to find the old one disconnected. Installed new one anyway. When connected it started up smoother (normally starts up rough) and ran a nice smooth idle. But the hesitation was even worse when driving at speeds, so disconnected sensor again.
Any advice on what the problem may be?
/M

[bpu699]

If you dont have an AFR meter, get one. absolutely mandatory to diagnose most anything with these cars...

Black smoke usually means you are running rich... if you had a boost leak that would do it. I have the same intercooler, and despite putting in new sealing rings, I am not convinced its air tight. How many o-rings do you have? The location where the intercooler meets the intake is supposed to have 2...

Also, putting in a larger intercooler may have altered your air-fuel ratio. You could try playing with the idle mixture adjustment, turning it clockwise a couple degrees to see if it helps...

Other option is to put the original intercooler back on, to see if the problem goes away. If it does, its a boost leak or air/fuel ratio issue.

Good luck!

[Rich76_911s]

I had this same issue. My work around was installing a boost controlled solenoid valve offered by Brian leask. Adjustable 930 WUR Website

This I found to be a workaround that improved the cars performance significantly, but I wouldn't say I fixed or located the root problem.

My hypothesis is that it has something to do with the lamda system and its relationship with the frequency valve. But I'm fan from an expert.

[Motte]

bpu699 : By "intake" I assume you mean the connection to the Intake by-pass assembly (Diverter valve) right? I have 2 (orange) o-rings on this. I will try to go back to original intercooler and see.
Rich76_911s : I heard about the Leask RPM CSV - will look into that option.
Thank you both for your insight. Others please chime in if you have opinions.

[bpu699]

Originally Posted by Motte

bpu699 : By "intake" I assume you mean the connection to the Intake by-pass assembly (Diverter valve) right? I have 2 (orange) o-rings on this. I will try to go back to original intercooler and see.
Rich76_911s : I heard about the Leask RPM CSV - will look into that option.
Thank you both for your insight. Others please chime in if you have opinions.

Mine had 2 orings where it attaches to the throttle body...

I could never find installation instructions, so its not clear to me where else they intended double o-rings...

Plan to pressure test my system this weekend (I have been thinking about doing it forever)... Lately I havent been hitting full boost...

[Rawknees'Turbo]

As others have mentioned, what you are experiencing is a very rich, full throttle (boost) condition - if you had an AFR meter on board, it would show AFRs in the 9s (should be in the 11s - 12 under boost) . . . anything much below 10 and rich misfiring starts to happen and is worse the richer it goes.

Since this just happened when you made intake component changes, you've likely introduced an air leak that causes the air metering arm to travel down farther than it actually needs to, under boost, and thus, excessive fuel is being sent to the injectors.

If no air leak(s), then the full throttle enrichment control pressure is too low and not putting enough resistance on the air metering arm/piston, causing to much fuel to reach the injectors. You would need an adjustable WUR to correct that, though (along with an AFR meter).

The lambda 02 sensor is not a factor during boost - the throttle position switch takes it out of the equation and the frequency valve goes into a "non correction" duty mode then.

[RarlyL8]

At the same time I replaced the O2 lambda sensor, just to find the old one disconnected.

If the Lambda sensor was disconnected the idle mixture should have been turned up to compensate. If so then you would run rich when the loop opens (boost).

Did you mess with the BOV plumbing at all? Verify the bypass valve vac line is plugged in.

[kevin930t]

I had a similar problem not long ago,and it turned out that i was missing the second o-ring that goes into the manifold making the car run rich especially on boost. Rawknees smart fellar

Sent from my SM-N910T using Tapatalk

[Rawknees'Turbo]

Originally Posted by kevin930t

Rawknees smart fellar

Sexy, too!

That was really cool to be able to help long distance, troubleshoot via phone text/pics - happy it worked out!

[Motte]

Hi all (and thanks for all the suggestions). Still have the issue.
I replaced the Andial with the original IC but no change except I felt less power. It still blows black smoke when I hit full boost around 3000rpm, still mostly in 3-4th gear not so much in 1-2nd. So guess the Andial is not the culprit at all but adds significant power.

Brian - I only removed the big rubber elbow on the BOV when I removed the smog pump equip, but that's before pressure. Did wiggle the downpipe to the Turbo a bit when installing the IC. Will try to take it apart and check if it sits tight.

Just for the hell of it I checked if both fuel pumps are functioning and they are - tried starting with both pumps individually and switched the relays and seems to be working fine.

Regarding AFR - which system do you guys prefer?

[RarlyL8]

If you hit full boost at 3000rpm now I'm going to assume that part didn't change, you hit full boost at 3000rpm before the swap as well. If so then if you do have a boost leak it is small. Check the turbo to up-pipe O-rings as they can pinch and become sliced very easily. When that happens they can seal fine until full boost is hit, then seal back up off boost. That up-pipe can also push off the turbo if the pipe is not clamped down well. Nomatter what you must verify the system is sealed before troubleshooting other possible culprits.

[Motte]

I will check this.

Does anybody have an idea why it is only in 3rd or 4th gear I get the smoke?

There's a minute hesitation in 1-2nd at 3000rpm and I can continue to redline, however if I lift off when on boost in those first gears, car jolts a bit and backfires on decel.

In 3-4th the black smoke kind of chokes the engine.

[Rawknees'Turbo]

Originally Posted by Motte

Does anybody have an idea why it is only in 3rd or 4th gear I get the smoke?

The 3rd and 4th gear deal is due to the load placed on the engine in those gears/speeds (much greater load, and need for fuel, than the same RPM in 1st and 2nd gear).

[RarlyL8]

There's a minute hesitation in 1-2nd at 3000rpm and I can continue to redline, however if I lift off when on boost in those first gears, car jolts a bit and backfires on decel.

Can you verify the ignition is not weak or breaking down? How do the plugs look?

[Motte]

How can I verify this? I checked the cap and rotor and everything is clean inside dizzy. Cap/rotor and wires was changed 10k miles ago in 2011.

Reinstalled the Andial. I cleaned downpipe and seals/o-rings and put things carefully back together - things improved quite a bit. More power now and feels more linear on boost. Signs of the hesitation/smoke is still there but now much less and now pretty much only in 4th.

[RarlyL8]

Pull your plugs and clean, they are likely coated from the previous issue. If so you are good!

[Motte]

Update:
Found out the remaining smog spider piping was not plugged properly and was also leaking through small holes near the nozzles. Removed the spider and plugged the air injection holes. Now the boost hits hard and fierce.
Thanks everyone for your help!!

[Airkooled]

Glad I found this old thread, I will chime in and second the boost leak problem RarlyL8 suggested. One day my 1987 930 began to hesitate under a load between 3 & 4k rpm, and only in 3rd and 4th gear at less than wide open throttle. I pulled the intercooler, reseated the up pipe, tightened the clamp down again, added a second orange o ring to the intake, thanks kevin930t, and viola, all good again. Worth noting, the car pulled fine at WOT, makes me think a small leak is all it takes to mess things up. Who knew there was such precision in the old CIS. Thanks Pelican Forum!