[DML] Hot exhaust - continued

["Nick" <nicholden@xxxxxxxxx>]

I will try answer all the questions below:

I have had the intake off several times and replaced O rings etc. I 
dont feel there is an air leak anywere and i have poured water 
around the intake port area while the engine was runnig to see if it 
sucked in anywhere and ran rough. It didnt.

I am aware that to much fuel would normally cause a cooler temp but 
i now have to look at the impossible as i seem to have ruled out all 
the possibles....The occasional flame out of the exhaust is what has 
me confused out of an engine that is reading correct mixtures and 
timing.
So how is that raw fuel getting into the exhaust if the timing is 
100% correct and mixtures reading OK? 
The exrtactors are very black inside when removed. 

Bear with me for a minute .... Just say for what ever reason i was 
not getting enough air into those 2 combustion chambers, is it 
possible that the fuel is not completely buring in the combustion 
chamber and sending raw fuel into the extractor and ingniting with 
heat causing the excessive extractor temp i am seeing?

>Nick, in my experience, flames out the exhaust or the intake is a 
>timing issue!  What are you using to control the ignition?
>on
I am running a Haltech computer and the timing has been checked a 
number of times by myself on each individual cyclinder and by the 
Haltech software engineer as we thought the same thing but it all is 
spot on.


>It is not too little air, it is too much air and running lean which
>gives the higher exhaust temps. Either add fuel or find the air 
>leaks.
>A final possability is a large amount of carbon build-up in the
>combustion chamber causing very high combustion pressures.
>David Teitelbaum
>vin 10757
The spark plug color is the same across the whole engine and is 
a 'Nice' color and would not indicate a lean or rich mixture. I have 
an O2 sensor on each bank (3 into 1 collector) and that also 
indicates correct mixtures.
The engine condition would not indicate excessive carbon but i had 
originally sprayed a 'carbon' spray into all the intake ports and on 
top of the piston. It getts excessively hot almost instantly. I will 
look harder for a possible an air leak but i dont feel i have one.


>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 am running a custom computer that controls all the EFI and duel O2 
sensors so i have no frequency valve. The computer enriches the 
mixture under boost. During normal operatin we are not running an O2 
sensor i have them in there for test purposes only as the mixtures 
are set right through the rev range on the dyno based on boost, load 
and ignition map etc.
The guy who wired the car and injectors has double checked his work 
and i have had the injectors tested and also swapped them on the 
affected cyclinders. Also as mentioned above the plug color and O2 
sensors would not indicate a lean mixture.
To remove any possible fuel delivery issues it is running multi 
point at the moment not sequential, this means all cyclinders are 
been delivered the same amount of fuel across the whole engine. 
I agree that it is something to do with the fact these two 
cyclinders are next to each other and not a coinfidence!

The reason this problem was detected was becasue on the dyno at 
around 400rpm it started to ping very badly and we had to shut it 
down. On invistigation i noticed that the ceramic on these 2 
extractors was very discoloured. I then tested them with a temp 
probe to see that they were 200 +deg C hotter than the others and 
this excessive temp i presume was causing the pinging/detonating.

Thanks for all the comments, i will eventually find this problem (I 
hope)....

Cheers, Nick - Sydney

























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