Jfrahm

HI all. I am bringing my 87 928s4, auto trans, stock out of semi-storage and when warming it up it started to smoke from (I think) under the airbox, probably on the LH side nearer to the brake booster (USA left hand drive).
Smoke started to come out behind the dash also but I think the source is more under the hood.
At first I thought it was dust or some drips burning off but after 60 seconds or so I could tell it was plastic/electrical.

I shut it down, that did not seem to help, then went back and disconnected the battery at the toolkit. Needing to get in there FAST is a good reason to replace saggy hatch struts. Also the linesmans pliers in the toolkit helped me unstick the butterfly nut on the ground strap.

Shutting the car off and taking they key out might have been all I needed to do as it still smoked a good while.

Any ideas? Blower motor? Blower resistors? I do have Magic Blower Syndrome.

Thanks,
-Joel.

Jfrahm

Update:
I do not think it's a key-off problem. Key off, I see 1.4A with the dome lights on, 0.02A with everything closed up. The car does drain the battery if left for a couple weeks.
Key on, I see 10-12A, no smoke after a few minutes. The AC blower seems to work.

dr bob

One of your ignition systems has failed. The catalysts were overheating and starting to burn the undercoating.

Fix it before driving. Short engine runs only as you diagnose. Charged garden hose handy. Work outside away from the house so you don’t take the structure with you.

Jfrahm

I'll check that. It might also have been a plastic bag or something stuck to the exhaust. I think it was idling too smoothly to have been on 4 cylinders.
--edit-- It might have a stuck injector which I suppose would fire up the cat as well.

Thanks,
-Joel.

G8RB8

critter nest

Jfrahm

No critter nest. Car was indoors and I keep mousetraps loaded and ready in the shop.

Possibly some of the undercoating is roasted, I am not sure what that looks like. It's flooding out and not starting unless I pull the fuel pump relay so it's got way too much fuel. It runs a long time with no fuel pump relay (XX) so I think it's getting a puddle of fuel.

Temp 2 sensor readings seem correct, coolant is warm and readings are 0.9k ohms both channels. I'll check them again later to see if the resistance goes up as the engine cools off.

Thanks for the help so far. -J.

Mrmerlin

swap your MAF then the LH into another running car

dr bob

Running too rich (from a failing LH?) would do a similar deed on the cats, and it sounds like you are experiencing that. LH controller been rebuilt yet?

Expanding some on the burning-cats diagnosis: There are only a couple cables in the area under the booster, and those are the battery to starter, starter to alternator, starter to ABS primary feeders. Everything else is forward of the oil filter and alternator. You can inspect those cable sections pretty easily for melting and escaping-smoke discoloration.

The car idles and runs at low speeds/loads in 4-cyl mode almost transparently. If one ignition fails, the engine runs on every other cylinder in the firing order, with the not-firing cylinders feeding raw fuel into the catalysts. The extra fuel causes the catalysts to overheat, and eventually the heat makes its way around heat shields to the tub. Undercoating and paint melt and burn on the bottom, carpet and central electrical panel melt and burn after a short while on the inside. '89+ cars have an "ignition protection relay" that shuts down half the injectors based on cold exhaust temp under specific cylinders, telling us that the factory was aware of and concerned about the cars catching fire from ignition faults.

Oil on the headers would be another possibility except that oil has a particular fragrance when burning. Oil from a power steering hose has a slightly sweeter fragrance but it's still identifiable as oil smoke vs. the melting and burning PVC insulation odor that's similar to undercoating.


Do a visual under the tub around the catalysts, inspecting the primary wiring where it comes forward from the starter to the alternator. Look for oil and oil staining in the area, and for scarring in the undercoating above the heat shields that might tell you what was smoking.

Jfrahm

Good advice. I did some more testing:
1 - Fuel rail fuel pressure gauge - IMO these are a Long Beach BBQ waiting to happen but it's what I had. Also put a switch place of the XX relay
1a - Key off. pump forced on:
1aa - Fuel pressure looked normal
1ab - Dropped to zero fast when pump switched off
1b - tried to start, car was flooded right from the get-go despite never having been cranked since it was cleared and run out of fuel at the rail days ago
1bb - This suggests to me that it's a hosing injector as the ECU or MAF would have needed to be operating to flood the car.
1c - cleared the flood with the pump off and the car idled OK until it ran out of fuel

2 - Swapped in a known good, rebuilt LH ECU
2a - Switched on the fuel pump and tried to start
2b - Car ran as it did with the original ECU
2c - had to shut off the fuel pump to get it to idle and clear flooding
2d - Big one - The rail gauge's needle bent below zero - vacuum in the fuel rail.

So I think it's a stuck injector, which also explains why it'd idle for a long time with the fuel pump off when I had the rear wheels on ramps dealing with the ATF. Vacuum pulling fuel through the system.

dzaprev

What about bad pressure regulator?

dr bob

Vacuum in the rail -- comes from somewhere. Options are fuel pressure regulator or one of the dampers. Easy enough to check each one with a MitiVac on the vacuum port. If the diaphragm won't hold vacuum, it's leaking. The vacuum will draw fuel through the leaking diaphragm into the intake, explaining the apparent flooding symptoms.

Taguid

Yep, sounds like dampers or FPR. Check them with a mighty vac to see if they hold pressure or smell of fuel.

Jfrahm

Front damper is OK but you might be correct about the FPR or rear damper. I have not exposed them yet.

Jfrahm

OK wow that FPR is leaking a lot of gas. Like 12oz a minute, I shut down the hotwired pump (engine off) after 30 sec with half a beer can of gas to then dispose of. Dang.

I've gotten the FPR out and most of the fuel lines off for re-hosing, the one to the fuel cooler is pretty stuck or I'm doing it wrong. Going to research that.
[Update: Got it with a 17mm/15mm flare nut wrench with the unused 15mm side fitted to a 1/2" hex socket on a breaker bar. Plus war cry.]

Dampers seem fine, hopefully they'll last a while. The rear one is $$$.

Thanks,
-Joel.

Jfrahm

Resolution:
Thanks all for the advice and on-target remote diagnosis.
I got a new Standard/Intermotor FPR to replace the leaking one, $92 shipped. Happily in the box was a Bosch unit.
Replaced all the rubber lines up front with modern, appropriate fuel line. Hose barbs dulled and hoses clamped appropriately (IMO).
Injectors backflushed and cleaned, new O rings, injector clips very carefully checked. Oddball 5-0 motorsports lower O rings (16,5mm).
The plugs are probably black and I'm worried about the O2 sensor, but the car ran great after about 20 minutes of idling and running.
Not on fire, no leaks.
I took it for an emissions test and it passed with great numbers. Bought new plugs, I'll get those installed in a bit. Originally I planned to do the plugs before the smog test but it was running fine so I thought I'd give it a go.

I might write up the injector work, it's pretty weird in a 1987. One bank had O rings and the other had those strange seals that look like a chunk of fuel line. I kinda like those, the O rings are a bit iffy in the odd oversized S4 injector ports.
I added a small O ring on the shoulder of the injector to better support the injector in the event a clip is not installed correctly. With this (2mm cross section) ring in place the injector cannot pop down out of the rail and leak fuel.
A copper sealing ring might also work but the OD needs to be small, the copper washers I have on hand are too large OD.

Thanks again,
-Joel.

p.s. A better solution IMO would be to fire up the lathe and make inserts that fit the standard lower O rings and locate the injector positively.