[DML] Re: Hot Exhaust - continued
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[DML] Re: Hot Exhaust - continued


Your project looks cool! See my comments embedded below.

-Joe Kuchan

--- In dmcnews@xxxxxxxxxxxxxxx, "Nick" <nicholden@...> wrote:

> From a dead cold engine extractor 1 & 2 is getting 200deg c hotter 
> after just 2 minutes of running at about 1500 rpm.
> Could a lack of air to those two cyclinders be causing excessive 
> temps? 

Comment: No. If anything, too much fuel would make them run cooler.
BTW, the PRV intake is held on by just four puny 7 mm bolts, and the
individual intakes are sealed by o-rings that can easily come out of
place when installing the intake. A loose or stripped intake manifold
bolt on the passenger front part of the manifold could allow it to
admit unmetered air, most of which would go to cylinders 1 and 2. An
out-of-place o-ring on cylinders one or two would also prevent the
manifold from seating properly. These kinds of defects would likely
have been caught by a smoke test, which you said you have done, but
not necessarily by a leak-down test since that is done with both
valves closed. When you did the smoke test, I assume that you pumped
smoke into the intake. Is that correct? Did you watch for smoke
leaking out under the intake in the area of cylinders 1 and 2? I can't
help but think that the fact that these two cylinders are adjacent is
a clue to the problem.

Extractor 3 was also slightly dis coloured but not showing the 
> same excessive temps when running. The way the air enters my manifold 
> it may be possible it is mainly been directed to the other bank and 
> starving 1,2 &3. I am at a point now that i have to look at everything.
> The plugs on 1,2&3 would indicate it is not a fuel problem but it did 
> occasionally blow a flame out of the exhaust on decel. that would 
> indicate raw fuel in the exhaust. 

Comment: A flame is pretty extreme, but remember that when the
throttle plate slams shut on rapid deceleration, the air flow is cut
off nearly completely almost immediately, leaving fuel nowhere to
complete combustion except in the exhaust. This is the cause of the
cool "popping" sound you hear from performance exhausts during
deceleration. A flame indicates excessive fuel in the exhaust, however. 

> My theroy is that due to a lack of air in Cyc 1,2 the fuel is not 
> burning correctly and in the combustion chamber and igniting in the 
> extractor. Cyclinder 3 is not geeting as hot becasue it is still 
> getting a small amount of air as it is the first cyclinder on that 
> bank.
> Any other thoughts and comments are welcome!

If several cylinders are running too lean for some reason (bad
injectors, wiriung harness problems to the injectors, flase air, or
whatever) the lambda probe (O2 sensor) will see that and attempt to
make the mixture richer using the frequency valve. Since the DeLorean
has just a single O2 sensor watching the ENTIRE motor (Is that still
true on your car?) a couple of lean cylinders will make the ECU try to
enrich mixture. It can only enrich ALL cylinders, with the result
being that if all cylinders EXCEPT 1 and 2 are running normally, then
1 and 2, which are running lean will cause the rest of the motor to
run rich.

Have you done anything to provide enrichment under boost? If so, what
have you done?

I think you have an air leak into cylinders 1 and 2. I think the O2
sensor sees this as a lean indication, and is trying to enrich the
mixture. The result is that all cylinders except 1 and 2 are running
rich, which explains the flame from the exhaust and the higher temps
in 1 and 2 than in othger cylinders. What were your temp readings
again? If my theory is correct, then all cylinders except one and two
will actually be cooler than normal, and while 1 and 2 may be hotter
than the others, they will probably not be as hot as they might
otherwise be if the lambda circuit were inoperative.

Good luck!

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