[s-cars] Re: 80tq: Opinions wanted

[Bernard Littau]

Hi Javad,

> The power loss is quite abrupt, pulls fine up to about 5krpm
> where the power
> loss begins, shifting restores full power until 5k rpm is achieved.  I'm
> convinced the coolant loss is a small head gasket leak, just not
> sure if its
> causing the power loss or not.  Consensus seems to be ignition related.
>
> One think I failed to mention, the first time the power cut out
> occured was
> very abrupt, I had turned boost up to 18psi, running very hard, had just
> passed a highly modded S4tt and all of a sudden complete power loss, huge
> cloud of black smoke, like I had run out of fuel, pulled in,
> turned the boost
> down and the problem had been occurring ever since, maybe this
> was the first
> time the HG went?

I'm thinking you might have an issue with your blow-off valve.  That, or an
issue with some loss of charge air at high pressure and flow.

While a "leak" is unlikely, the symptoms are very close to what I
experienced at much lower boost levels when I plumbed in my new intercooler.
I had a hose clamp too loose, and the hose slipped at high boost and leaked.
As soon as the boost came down, it "resealed" itself and the car drove fine.
I remember the black smoke and the abruptness of the power loss when the
hose slipped.

I'm leaning towards the blow off valve being compromised under high heat and
high boost situations.  Once damaged, it likely lets go more easily now than
the first time.

The black smoke makes me think rich, which would be consistent with a leak
or a blow off valve actuating (or ignition cut out).  I would expect white
(coolant) if the head gasket is blown, or perhaps blue (oil), but I can't
see black being generated by a head gasket issue.  (If you leaked enough
coolant to quench combustion, to make rich, you would have other signs of
the problem.)

It might be interesting to try and rule in or out an ignition event as the
cause of the problem.  You might consider installing a relay on the main
wire to the coil, and controlling it with a switch in the cockpit.  Have a
passenger interrupt the ignition while you power through 5k rpm and see if
the visceral feel and physical evidence (black smoke) are the same as with
the on track event.

Best,

Bernard Littau
Woodinville, WA
'88 5ktq