-----Original Message-----
From: Jim Lill [mailto:jpl@vectorbd.com]
Sent: Wednesday, August 26, 1998 3:20 PM
To: John Goodyear
Subject: Re: Peugeot geniuses Help A StarQuester.
who makes the ECU and injection?
-Jim Lill http://www.vectorbd.com/users/jpl
On Wed, 26 Aug 1998, John Goodyear wrote:
> Fuel Injection Gurus,
>
> The Hot topic of the 87 Starquest fuel cut has surfaced again with, a new
> twist. Scott Lambson posted this asking for comments. I ask you to
> consider it as a possibility and comment. Please also take a look at my
> other message on fuel cut that went unmentioned.
>
>
> SCOTT:
>
> Clark posted a question as to why he was not experiencing the proverbial
> fuel cut in his 87. I have conversed with him about this before to which I
> had no idea why
> he has not been experiencing fuel cut. But, it got me thinking. I have
never
> had it in my 87 either.
>
> Now, I have been on these Starquest BBS about 4 years now and have had my
87
> for longer than that. I had never heard about a fuel cut until I got
Topends
> catalog and I bought it about the ECU needing upgraded but I could not
> afford to have my car down for 2 weeks. So I waited and asked some
> questions. Everyone
> on the boards kept telling me that the 87's had a fuel cut somewhere
around
> 14.5psi and the 88-89's was set somewhere around 18psi. I believed them.
> And, I
> proliferated that information.
>
> I have been searching the manuals for anything concerning something about
> the fuel cuts. I have found NOTHING. I have manuals for the 84's and 87's.
> (If you
> know of something please direct me to the page.)
>
> Which got me thinking even further. How would the ECU know when 14.5psi is
> met?(retorical) Anyone who still believes the stock boost guages is actual
> pressure
> or is even accurate, I can produce the schematics to prove them wrong. The
> boost guage is based on two sensors. Mainly the counts coming from the Air
> Flow
> Sensor(AFS). Secondary is the engine speed sensor. So as more air flows
> through the measurement tube more boost is shown. In stock configuration
> this can be
> fairly accurate. Unfortunately most of us modify these cars.
>
> You can get around the fuel cut by modifing the AFS but you also make the
> car run leaner. According to what I understand of the ECU operation, fuel
> cut is actually
> determined by pulses coming from the AFS or more specifically frequency of
> the pulses. At some set frequency the ECU initiates the fuel cut. Fuel cut
> should occur
> like this. Timing starts retarding, fuel trim stays the same and boost is
> cut back. Unfortunately, the ECU has no control over boost pressure other
> than to adjust the
> timing. The DSM's use a boost control solenoid the drop the boost when
> excessive knock or fuel cut is reached.
>
> Everyone that claims to have reached fuel cut explains it as a sudden
surge
> of non-acceleration which quickly corrects itself. In order for this to
> happen fuel would
> have to be cut. Most likely done by the ECU by not opening the injectors
or
> cutting the frequency driving them. This seems like a really bad thing to
> design into an
> ECU. But it is possible.
>
> The other thing that I would like to propose is that there is no fuel cut.
> O.K. this may be a shocker but I am starting to think we have all been
feed
> a line of bull. My
> hypothesis is this. Somewhere around 80% duty cycle, most injectors reach
> saturation or they will not cycle accurately anymore. This is due to the
> fact that there
> simply is not enough time left to open and close. Our injectors are a
> slightly different breed. My understanding is that they are run on a
50%duty
> cycle continuously
> but the actual frequency that they are driven at changes.
> _________ ________
> _| |_| |_ normal injector @ 80%
> _ _ _ _ _ _ _
> _| |_| |_| |_| |_| |_| |_| |_ Our injectors at saturation
>
> Our injectors reach saturation when the frequency gets high enough that
the
> time on and off does not allow the injector to open and close. So, what I
am
> proposing
> is that 'fuel cut' people are experiencing is not actually fuel cut but
> rather injector failure. Contrary to popular belief the stock injectors
will
> not get you over 250
> horsepower at stock fuel pressures.
> According to everything I have gotten from the experts the combined total
of
> the stock injectors will flow around 1250cc/min of fuel. Go to
>
> www.rceng.com
>
> There is some good explainations of fuel injector theory. And even though
> their site still says they sell injectors for the StarQuests they should
> tell you they won't.
> Maybe, a good pestering will bring them back.
> Anyways, the formulas there will tell you the stock injectors are a little
> weak even for the 250 horse range.
>
> I personally am running two things to correct the fuel problem. 1. A BCFPR
> which raises the stock fuel pressure at boost. This gives you some
expanded
> fuel
> capacity when you need it. 2. Larger injectors from RC Engineering.
> According to my calculations this should get me close to 275.
>
> I have talked to Topend about their 87 ECU and have not been able to get
any
> concise information. My assumption is that what they are doing is to add
the
> 88-89
> fuel maps and ingition curves. What they do physically is to add a
> daughterboard. If anyone has any proven info. let me know.
>
> Maybe I am way off base here but I figured I might as well post my
concerns
> as I would like to see a disertation as the the reality of an actual ECU
> fuel cut. I
> welcome any corrections.
>
> New Message:
>
> : Sorry about the ASCII stuff. It did not come across to well. Just
assume
> the top of the pulses are line up with the next line. The nomal injector
> should have big spaces on the on pulses and small spaces the off pulses.
>
> : On Off
> : _|-------------------------|_|------------------------|_
>
> : _|--|_|--|_|--|_|--|_ Ours
>
> : Heres another site at greddy.
>
> New Message:
>
> : At saturation
>
> : : off.........on...........off
> : : _|-------------------------|_|------------------------|_
>
> : : _|--|_|--|_|--|_|--|_ Ours
>
> : : Heres another site at greddy.
>
> : http://www.greddy.com/injectionsizer.html
>
>
>
> What Do you guys think? Is he way off base or could it happen?
>
> Below is A Question I posed back:
>
> : Scott,
> : A quick thought, Lets say topend was putting in the 88/89 fuel map in
the
> 87 ECU conversion. If your theory was correct, wouldn't the richer 88-89
> fuel map driving the unchanged 87 injectors cause them to fail even
sooner?
>
>
> Thanks All,
> John
>