PRV Hunting - response.

["mgutkowski@xxxx" <webmaster@xxxx>]

Hi All

Here's a collection of points written by Darren in response to mails I
forwarded to him off the DML, and general chatting with regards the PRV
hunting. There's some other info in there about how to set up the fuelling,
and also a reply to Bill identifying his engine. I hope it's interesting
and not _too_ long.

Martin
#1458
#4426

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My opinions will probably keep the guys across the pond "cussing" for ages!
At the end of the day I know what works and when I build an engine it has
to run perfectly, and they always do, or else a running fault could cause
premature wear of the new engine (probably the reason the engine wore out
in the first place). Many of these guys with opinions have cars that
hunt......That is the case for the defence your Honour :-) Shain makes the
most sense. I am beginning to believe it is a problem with vacuum leaks;
perhaps we are getting too deeply into the fault and it is nothing more
than 20yr old rubber O rings are no longer sealing properly when cold. I
know that when I strip a PRV the inlet manifold O rings are squashed and
turned from rubber to hard plastic.

To the guy who suggests disregarding the Renault manual; the Renault k-jet
manual is written by Bosch and it does cover Lambda vehicles (Switzerland)
as it is written for european vehicles but I can see how he comes up with
that idea not having seen the Renault manual.

There is no way a variation in cylinder pressures or spark plug variations
would cause an engine to hunt, in fact one running on 5 cyls would not
hunt, it would idle slower which would then be corrected by the idle valve
and then held steady by the valve if set up correctly. I suspect that even
someone who has been working on DMC's for years would not know the correct
setting proceedure as it is not in the DMC manual and they would be
unlikely to get hold of a Renault manual as Renaults are not sold in the US.

It appears that DMC didn't want unskilled people messing with the settings
but Renault had no proplems with giving the dealers the info to set them
up. To set the idle you clamp off the pipe to the idle valve and set it
with the brass screws as per engines without idle system, ie remove and
clean the screws, refit them and screw them all the way in. Back off the
two front ones 2 turns and then set the idle with the back screw to 900
rpm. It is absolutely critical that the control pressure is correct (3.4
bar) and that the pressure from the pump is correct (4.8-5.2 bar). The only
thing you can't do on the DMC is set the co which should be 0.7-1.0 before
the cat. The idle should not vary when cold and the manual gives all the
testing proceedures and values of electrical sensors etc.

A simple way to set the mixture screw with out a co meter is to bridge the
fuel pump relay with the engine off, pull out an injector and put it into a
container and put a washer (about 0.5mm-1.0 mm thick) under the air plate
stop to hold it in the same position as at idle and turn the mixture screw
untill the injector "cracks" which is the point at which the injector
starts to spray. Then set the idle...

The K-jet system will handle more than 140 hp,the standard Volvo 760 is 170
hp in european spec without cats. The Renault 5 Turbo 2 (mid engined) used
the PRV metering head and produced upto 350hp from 1400cc in tarmac rally
spec! I also used to prepare a Golf GTi 1.8 with K-jet that put out 190hp,
although the idle had to be set at 2000rpm because at low speed the pulses
that came back up the inlet manifold upset the flow plate, that is the only
problem with k-jet when the cams get wild. The pulses push the flap shut as
the pulses going in are trying to push it open when you run cams with alot
of valve overlap resulting in no air movement which equals no or very poor
idle. Obviously the active idle speed valve was not designed to operate
with toblerone shaped cams with big overlap, it was designed to give a
steady idle dependent of engine load with standard cams.

-------

(Bill's engine)

Ah, The Renault 30TX is alive and well and living in a DMC! The injection
system Bill describes is Phase 2 R30TX. I have actually got a factory
bulletin from Renault advising how to retro-fit this system to a phase 1
30tx that has running faults (phase 1 had the same as DMC). The metering
head is alloy, not cast iron, the fuel lines are solid steel pipe and it
has a conventional fuel pressure reg as well as a k-jet pressure reg to
improve throttle response. As to a lack of power, it should produce more
power, as in the Renault it gives 144bhp from a 2664cc PRV. The lack of
power could be down to the distributor not giving enough advance if it has
a DMC dizzy.If he wants a Renault dizzy I have them in stock, but he needs
to get the advance checked first. The supplied engine number for Bill show
140 which is a Renault 30TX engine out of a phase 2. It may lack torque off
the line as it is only 2664cc! Sounds like he needs an engine building to
2849cc..... 

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