RE: [DML] Hot exhaust - continued
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RE: [DML] Hot exhaust - continued



Nick,

See my comments below.

-Joe Kuchan


>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.

The water approach is not the best idea. Hydrolock is not fun! Use carb 
cleaner instead. (i.e. something that will burn rather than lock up those 
cylinders.) or propane. (Be careful!)

>
>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....

Don't look for the impossible. The impossible is just that. You haven't yet 
ruled out all the possibles. You just don't know what it is...yet.

>The occasional flame out of the exhaust is what has
>me confused out of an engine that is reading correct mixtures and
>timing.

When you say it is "reading" correct mixtures, what do you mean? How was 
this measured? Are you still using a single O2 sensor to monitor the entire 
engine? Did you use an exhaust gas analyzer? How was this confirmed? In a 
case like this it is important to REALLY know what you think you "know"! Be 
aware that a single O2 sensor is going to monitor the entire engine, which 
means it will be "happy" even if SOME cylinders are too lean and others are 
too rich. It will see the average of the entire engine. Modern setups 
monitor banks of cylinder separately and give you a finer degree of control 
and better troubleshooting information when they detect anomalies. What does 
you car have for O2 sensors? I believe that flame you're seeing is an 
indication that some of your cylinders are way too rich, but not cylinders 
one and two! The knocking under boost and higher temps in 1 & 2 most likely 
indicate a lean condition in those cylinders. You need to find out why. 
Perhaps those injectors are sluggish and at higher rpms they are not passing 
enough fuel. Or perhaps you have an air leak. They are NOT running too rich. 
If anything, OTHER cylinders are running too rich as the engine controls 
attempt to keep the mixture correct while those too cylinders are too lean.


>So how is that raw fuel getting into the exhaust if the timing is
>100% correct and mixtures reading OK?

See my answer above.


>The exrtactors are very black inside when removed.

Which extractors? All of them? Just 1 & 2? All except 1 & 2?

>
>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?

Possible I suppose, but that is NOT consistent with the knocking. Also, for 
that to happen there would need to be an exhaust air leak for the fuel to 
burn where it is burning. Without air to burn, that fuel will drip out of 
the exhaust pipe before it would burn just outside the head. Do you have an 
exhaust leak there? A lean condition is consistent with the knocking. A lean 
condidtion in just those two cylinders would cause the knocking AND the 
flame as the other lungs run rich in an attempt to compenaste for 33 1/3% of 
your engine (2 out of 6 cylinders) running too lean. Have you moved those 
injectors yet to see if the problem moves withthem? If not, do that. Have 
you used an oscilloscope to confirm that waveforms AT THE INJECTORS (not at 
the Haltech) are correct? If not, you may have a harness issue.

>
> >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.

At what RPM? If you do not test this at the problematic RPM, you still don't 
know for sure that all is well.

Good luck!

>
>
> >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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