86 930 very rich black smoke and missing

[unclebilly]

I tried to take my 86 930 for the first drive of the year tonight.

It started up really well and idled nicely as I went and locked the house (we do this now). Then it stalled.

I got a 1/4 mile from my house and it started to run super rich, black smoke, missing, and would not rev up.

Oddly, if I start it, this is how it behaves but if I shut off the ignition, it runs perfectly until the ignition cuts.

I’m thinking my fuel pressure regulator is haywire from sitting over the winter even though I started it periodically.

What are your thoughts?

Currently my 11 year old son is towing my back home with our quad.

[gsxrken]

Check your 2 red fuel pump relays on the front fuse box.

[unclebilly]

The red relays didn’t seem to do it.

[356911930]

Hi Billy,

It could be the "piston" in your fuel distributor has had the gasoline turn to varnish and it is stuck allowing too much fuel. You can pull the top off of the fuel distributor and you can clean the "piston" with acetone or similar. The "Piston" is very highly polished and you would not want to scratch it at all; even with the finest sand paper. When you take the top off the fuel distributor the piston is able to just fall out so be sure to not let this happen.

Best of luck,

Rahl

[gsxrken]

Originally Posted by unclebilly

The red relays didn’t seem to do it.

My guess is one of your fuel pumps dropped out, thus the red relay quick check. I had exactly what you described once, and it was due to my fuse box cover (that never stays on, dammit) had slid down and pulled one of the relays halfway out. They’ll run with just one pump, but super rich b/c the lower pressure provides less resistance to the fuel piston that the other poster mentioned. Rich is ok while it’s warming up but then not OK.
Checking cold and warm fuel pressures is always prudent when there is any issues with these cars, but if it starts and then shortly goes pig rich, whether it’s a fuse, a wire, a stuck pump, or a bad relay, it’s a good idea to make sure both pumps are running.

[RarlyL8]

^^^
First thought is fuel pump but you need to verify the fuel pressure to be sure.
If you have an AFR meter it is good to also verify that the AFR and fuel pressure are coordinated. Typical culprit is the relay or the fuse. The relay doesn't have to be hot, it could simply be dead. You can jump it to test.

[unclebilly]

I have a set of CIS gauges from when my 77 had carbs.

Is there a troubleshooting procedure somewhere? I have a 930 shop manual supplement somewhere but can’t recall if it covers this.

[T77911S]

remove the connector on the rear of the AFM to make the FP's run with key on and engine off.
turn key on. remove one relay at a time and make sure each pump runs. it should get noisier.

check for power to the WUR connector.

stuck piston as suggested.
with the FPs on and engine off check for pressure on the sensor plate. there should NOT be any play. you should also be able to push it down and hear the injectors. (i would start it after doing this so raw fuel is not sitting in the cylinder.

make sure you have no air leaks, especially on the pressure side if it is running rich.

[Zuffenwerker]

Originally Posted by unclebilly

I have a set of CIS gauges from when my 77 had carbs.

Is there a troubleshooting procedure somewhere? I have a 930 shop manual supplement somewhere but can’t recall if it covers this.

Here are fuel press. specs for the 86 turbo usa! Check your system pressure, control press. cold, and control press. warm. Whichever spec is off points you in the right direction.

Daniel

[tasturbo86]

Never hurts to put a new O2 sensor on it.
I never stalled, but it ran poorly until I change mine.

[mark houghton]

The only other thing that hasn't been mentioned would be a failure of one of the intercooler o'rings. If your charge air is allowed to escape, you will have a very rich condition that only gets worse as you raise the rpms. Try going on boost and you'll not only have a flat response, but you'll look like a diesel truck from behind.

[T77911S]

see post 8

[mark houghton]

Originally Posted by T77911S

see post 8

Ahh...so you did in your final sentence. I missed that.

[T77911S]

its ok
i miss a lot more stuff than i use to.
mineries does not help

[unclebilly]

Ok. Finally had a chance to monkey with this tonight… both fuel pumps run with the engine running. Will check pressures next and remove piston form the dist if necessary.

It’s crazy that it runs perfect when you shut it off.

[T77911S]

It’s crazy that it runs perfect when you shut it off ???

[unclebilly]

Originally Posted by T77911S

It’s crazy that it runs perfect when you shut it off ???

Yes. In the 2-3 seconds between when you shut it off and the ignition cut, it runs absolutely perfect.

[patina]

Have you tried simply adjusting the mixture at the fuel head? 4MM Allen key inserted into the plunger. In your case I’d try about a 1/4 turn counter clockwise.

[tasturbo86]

Sounds like too much fuel pressure.
I believe the pumps shut off when the key is turned off, but ignition has a slight delay?

[T77911S]

Originally Posted by unclebilly

Yes. In the 2-3 seconds between when you shut it off and the ignition cut, it runs absolutely perfect.

mine idles up and seems to idle better when i turn it off.

i have tried adjusting the mixture for best idle, but it still does it.