diesel gurus....please help!!!
Submitted: Wednesday, Apr 18, 2007 at 22:56
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S&N
i need help. if you KNOW what you are talking about regarding diesels, not just what has worked for you, please read and tell me your thoughts!
i went to a "REPUTABLE" diesel workshop in bayswater, asked about putting more boost in my 89 gq 4.2 turbo diesel. it has an aftermarket denco system. the mech lifted the bonnet and straight away tells me that my patrol doesnt have a boost compensator. and further, that it would be this that ione of the problems with my vehicle, as the fuel wont adjust with the boost. he then takes me for a drive in it and says its very sluggish and this would be because of the lack of a compensator. he takes me back to the office and shows me some info that he wrote and was published in a 4x4 mag. he also said that the tappets were noisy and the injectors needed to be done. (even though the guy i bought it off 2 years ago, is a diesel mech and he said he did the injectors just before selling to me) so all up, for injectors, fit boost compensator, increase boost to 10psi, and "tune for 10psi" i was quoted $2650. then that night i went to the berrimah diesel, diesel myths web-page and they state that you dont need one, and that there is very minimal gains to be had for spending $1000-$1800 on a compensator. they say it can be tuned without the compensator. i also read a comment that said if a compensator was needed, then why dont denco, mtx etc fit one as part of their package?
So.............. do i need to go spend the $2650 and have it done by them, or..... should i fit a boost guage, egt and manual boost controller then have it "tuned" (fuel matched to egt) on a dyno and that willl be fine?
please help as the $2650 can be spent elsewhere if its not a necesasary job!
thanks guys!
Reply By: hiab - Wednesday, Apr 18, 2007 at 23:34
Wednesday, Apr 18, 2007 at 23:34
reinholt at berrimah and his son andrew, are very good diesel men, the old fella can be a bit stubborn at times and set in his ways. i believe a fuel compensator, not a boost compensator, is a good thing, once the fuel pump is timed it cant be moved other than recalibrating, when the man you bought it off said it had new injectors did he say new, or just put nozzles in, inside the injector body are springs, shims, etc. he may have just put new nozzles in. if
the springs are worn they will open before they should and over fuelling will occur, result , black smoke. injectors should be done as a rule of thumb every 100.000 ks, noisy tappets will just be valve clearances, about 30 mins to adjust. the 4.2 is a strong robust motor and i think 10 pounds of boost is conservative, you could safely take it to 14/16 . and have the fuel adjusted accordingly, by the way, did the dude take the injectors out and
test them? i guess not. you have to
test them and look at the spray pattern.i would not go back to that workshop for anything. have your injectors tested at a good place like hy-flo or a place that is recommended to you by someone you trust. get them tested, have your valve clearances done, set your boost at , i dont know the ks of your motor, at say 12 , and i think you will be happy.
AnswerID:
234362
Follow Up By: hiab - Thursday, Apr 19, 2007 at 19:47
Thursday, Apr 19, 2007 at 19:47
sorry , i meant 12/14, talked it over with the guys at work at smoko and a great debate followed, we eventually agreed that 12 is about the optimum. 16, what was i thinking, you would have been picking up pistons off the road. one of the apprentices is the nephew of les siviour the off road champ and he ran a 2.8 with huge turbo and heaps of boost, went like the proverbial but was very fragile.
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Reply By: Snowy 3.0iTD - Thursday, Apr 19, 2007 at 01:57
Thursday, Apr 19, 2007 at 01:57
S&N
For high levels of boost a boost compensator is good. If you turn up the boost and turn up the fuel pump, you will get a good air/fuel mix at full boost but at low boost levels the motor will overfuel. If you don't turn up the fuel pump then at low boost levels the air/fuel ratio will be good but it will then run lean (& hot) at high boost. Having said all of that 10psi is fairly conservative and fitting a boost compensator is not necessary, even up to say 12psi you could get away without one, beyond 12psi it would be something I would recommend. As for the injectors as somebody has already stated every 100,000km is a reasonable service period, you just need to
check what was done to them. And as what most people do when spending this sort of money,
shop around and get a second or even third opinion.
Cheers
Snowy
AnswerID:
234386
Follow Up By: furph - Thursday, Apr 19, 2007 at 08:07
Thursday, Apr 19, 2007 at 08:07
Snowy.
For your
information a diesel running "lean" runs cool, not hot. It is exactly the opposite to a petrol engine.
furph
FollowupID:
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Follow Up By: Member - Matt Mu (Perth-WA) - Thursday, Apr 19, 2007 at 19:26
Thursday, Apr 19, 2007 at 19:26
Heer Heer Sowy!!
How sick are you of hearing that statement!! Lean in a diesel is 'Less' throttle so less power!How the hell does that make it run hotter???????
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Follow Up By: Snowy 3.0iTD - Thursday, Apr 19, 2007 at 20:43
Thursday, Apr 19, 2007 at 20:43
Happy to be corrected where I am wrong. I must not have been paying enough attention in my thermodynamics classes all those years ago when they were going through combustion theory. It was my understanding on just about all combustibles; gas, liquids, gels solids etc burn hotter when the the air/fuel ratio is higher, thats why the add oxygen to acetylene. The hotter the combustion process is the more efficient it is, the problems comes from the fact that the metal components of engines can only tolerate a certain temperature level. Like I said happy to be corrected though, I will have to dig out the text books and read up on the Otto cycle.
Cheers
Snowy
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Follow Up By: Go-N-Grey (WA) - Friday, Apr 20, 2007 at 00:42
Friday, Apr 20, 2007 at 00:42
Dont know about diesels, and could be convinced either way, but every piston engine pilot will know that you lean the engine to peak EGT (least fuel flow before losing power) and then enrichen 50Deg for best economy (to preserve the exhaust valves with cooling from the extra fuel which goes straight out the exhaust) and 75deg below peak EGT for best power.
On a 300HP fuel injected engine this makes a difference of 1-2 gph on the fuel flow.
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Follow Up By: Ian from Thermoguard Instruments - Friday, Apr 20, 2007 at 16:51
Friday, Apr 20, 2007 at 16:51
Hi Gents,
For my two-cents worth on the diesel EGT/'rich'/'lean' issue, you might like to have a look at this ExplorOz Tech Article.
There are also follow-up articles on turbocharging, intercooling and diesel injection systems. One on diesel injection control techniques is in the pipeline.
Hope this helps.
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