CIS problem
Thread Starter
Addict
Lifetime Rennlist
Member
Lifetime Rennlist
Member
Joined: May 2001
Posts: 3,966
Likes: 47
From: New Jersey
CIS problem
I'm sending this out to a few different list to see if anyone has experienced this issue with their CIS system.
Background:
Car is a 1980 928 EuroS w/5.0L motor, track only. Puts about 305hp to the ground (when running right!). I'm using a stock CIS system and had the A/F tested at 13.4 during a dyno run a few months back.
A few weeks ago I was at a Watkins Glen DE and had a issue the second day. The car seemed starved for fuel on the back straight. Was having a hard time making redline in 4th. The day before it was fine and flying!
I noticed the fuel was low when this happened, so I went back into the garage area to fill up and go out for another session about an hour later. Had the same problem, but it actually seemed a bit worse. It appeared 3rd gear was OK to redline, but that started to have issues also. I can only describe it as an old 4 barrel carb. opening it's secondaries and doing nothing for performance but making noise. You back off the throttle and it's better with no increase in speed.
So the first guess was that the 23year old fuel pump is going(filter changed last year). Ordered a newer style Bosch with a bigger output and pressure rating. Installed it, but that didn't help.
Car seems to run fine in the driveway until it's fully warmed up. Then it will start having a bit of a miss when the engine is reved to 4K. Idle is fine.
Here is the testing so far:
> > Control pressure did a slow rise as the car warmed up. Finally
> settled
> > at 37psi during idle (43 with car off). Leak down was fine. Held 43
> > after 30min. Would jump to about 40 with a rev and then back to 37.
> > This is with the vacuum line of the warm up regulator connected to
> the
> > motor. The closed pressure was 74psi.
> > Did no other testing with or without the vacuum line connected.
> > The car started to break up a bit when reved to 3-4K. Almost
> sounded
> > like a miss.
> > I then hooked up the gage to #1 fuel injector line. The fuel
> pressure
> > was pulsing from 35psi to 43psi. Almost the same frequency of the
> miss.
> > I also checked the voltage at the fuel pump. It was 10v with the
> relay
> > or with a jumper. I did apply 12V to the pump, but the fuel system
> did the same thing.
Any ideas? I'm leaning towards rebuilding the fuel distributor.
Thanks!
Background:
Car is a 1980 928 EuroS w/5.0L motor, track only. Puts about 305hp to the ground (when running right!). I'm using a stock CIS system and had the A/F tested at 13.4 during a dyno run a few months back.
A few weeks ago I was at a Watkins Glen DE and had a issue the second day. The car seemed starved for fuel on the back straight. Was having a hard time making redline in 4th. The day before it was fine and flying!
I noticed the fuel was low when this happened, so I went back into the garage area to fill up and go out for another session about an hour later. Had the same problem, but it actually seemed a bit worse. It appeared 3rd gear was OK to redline, but that started to have issues also. I can only describe it as an old 4 barrel carb. opening it's secondaries and doing nothing for performance but making noise. You back off the throttle and it's better with no increase in speed.
So the first guess was that the 23year old fuel pump is going(filter changed last year). Ordered a newer style Bosch with a bigger output and pressure rating. Installed it, but that didn't help.
Car seems to run fine in the driveway until it's fully warmed up. Then it will start having a bit of a miss when the engine is reved to 4K. Idle is fine.
Here is the testing so far:
> > Control pressure did a slow rise as the car warmed up. Finally
> settled
> > at 37psi during idle (43 with car off). Leak down was fine. Held 43
> > after 30min. Would jump to about 40 with a rev and then back to 37.
> > This is with the vacuum line of the warm up regulator connected to
> the
> > motor. The closed pressure was 74psi.
> > Did no other testing with or without the vacuum line connected.
> > The car started to break up a bit when reved to 3-4K. Almost
> sounded
> > like a miss.
> > I then hooked up the gage to #1 fuel injector line. The fuel
> pressure
> > was pulsing from 35psi to 43psi. Almost the same frequency of the
> miss.
> > I also checked the voltage at the fuel pump. It was 10v with the
> relay
> > or with a jumper. I did apply 12V to the pump, but the fuel system
> did the same thing.
Any ideas? I'm leaning towards rebuilding the fuel distributor.
Thanks!
Last edited by John Veninger; Jul 16, 2003 at 10:38 AM.
Drifting
Joined: Jul 2002
Posts: 3,348
Likes: 0
From: Los Angeles, CA
Sounds similar to when my fuel distributor died.
It seems like when it gets low on fuel, or the fuel pump or filter dies, then it can get metal particles or sediment inside, which screws up the delicate nozzles, etc...
I found that it slowly got worse and worse.
Either way, it seems like a good idea to replace the filter first anyhow.
If that is plugged-up, it could be causing some of those symptoms.
If that does not do it, you may want to look at other things, like the
fuel pump, and other systems, before dumping the time and money
into a rebuild of the fuel distributor.
It seems like when it gets low on fuel, or the fuel pump or filter dies, then it can get metal particles or sediment inside, which screws up the delicate nozzles, etc...
I found that it slowly got worse and worse.
Either way, it seems like a good idea to replace the filter first anyhow.
If that is plugged-up, it could be causing some of those symptoms.
If that does not do it, you may want to look at other things, like the
fuel pump, and other systems, before dumping the time and money
into a rebuild of the fuel distributor.
Instructor
Joined: Jun 2002
Posts: 247
Likes: 101
From: Milwaukee, WI
John,
Jean-Louis had this exact same problem with his 83 Euro racer last year. He is not quite sure what ultimately fixed it, but he took the entire fuel distributor system out and cleaned it and rebuilt whatever he could. Then when he got it all back together it was fine. You may want to email him and see if he has any more insight. Email me at ckkwas@wi.rr.com and I will give you his email address.
Jean-Louis had this exact same problem with his 83 Euro racer last year. He is not quite sure what ultimately fixed it, but he took the entire fuel distributor system out and cleaned it and rebuilt whatever he could. Then when he got it all back together it was fine. You may want to email him and see if he has any more insight. Email me at ckkwas@wi.rr.com and I will give you his email address.
