Eric Vaas

Hi guys,

Newbie here, but been reading this forum for a while, have not posted much. You guys are wonderfull sources of information thanks! Forgive me if this question has been discussed before, but I have a question about CIS system fuel pressure. I'm working on an '80 928S Euro 5-speed with CIS injection. The engine idles but does not rev up. I can see that the air sensor plate is not moving but I can press it by hand and it revs. I measured system fuel pressure, and it's to high, reading 6.8 bar when it should be ~5.5. Control pressure is good, at 1.5 bar. I recently replaced the fuel pump and filter. My question is will the pressure regulator allow this much adjustment? Looks like I need to adjust it a good 1.5 bar. To much? Or do I need to do something about the pump?
Thanks,
Rick

86.5 928S Auto
80 928S Euro 5-sp
96 BMW 318i
90 Anniversary Supercoupe
Various Mustangs
Buell

michael j wright

opening the throttle by hand should alow enough air flow over the sensor plate to move it and alow the engine to "rev" up. the first thing I would do is look for any vac leaks to see if you are sucking air from places other than the air flow sensor area. also might try adjusting co a little at a time. another area to look at would be the wur- if stuck might me under full enrichment- but you said that the controll psi was o.k. so may not be the problem, but I find mine runs better with vac lines disconected and pluged mine also has had some what of the same problem(but still revs-just not as good) the j shaped hose part# 928 110 177 02 at aux air reg was sucking air and causing a flat spot on accel - hope this helps and good luck!

jpitman2

When you say wont rev up, what happens when you open the throttle? Does it go lean or rich? Is there black smoke at idle? When you say airplate doesnt move, do you mean it doesnt move when you open the throttle? Is it touching the side of the casting and sticking?Cold control should be down around 1.5bar, but as it warms can come as high as 3- 3.5bar IIRC - 45-50psi. If it gets higher than 55psi, it wont rev .
Get a copy of Ben Watson book on Bosch Injection, it covers CIS well. Usually failure to rev is caused by high control when hot, and high control is mostly caused by a blockage in the WUR, or its return line. Has the car been sitting for long periods? If so, run some Techron through it to try to clean out crap. High system could be caused by a blocked return line. Here's a way to test for problems causing high pressure -
bridge the fuel pump relay, with pressure gauge installed; VERY carefully, with an extinguisher handy, crack open the closest joint in the return circuit (on the fuel distributor?) and see if pressure drops; if it does drop, the problem is down the line further; if it doesnt, the problem is back up the line. Each time it DOES drop , close the joint up, move to the next one - hose to body on RHS, then the tank return fitting hose.
Failure to rev can also be caused by low delivery rate - this should be ~1350ml in 30 seconds, at the return line on RHS engine bay.
hth
jp 83 Euro S AT 50k

Eric Vaas

Thanks for the replies.
I rechecked the setup last night, and (sorry) I had the gauge hookup not quite right. I had bypassed the WUR altogether. Now the gauge is in the control line source only. The problem is still there. My system pressure is to high (7 bar). But when I check the control circut, it is also to high, the same 7 bar. This suggests the return circut is blocked (maybe the WUR itself?). I took apart the pressure regulator, and dont see anything wrong with it. Its clean, and moves ok. I will do those checks next. To answer the questions:
1) When I flip the throttle, the motor just dies.
2) I think its to rich, as the exhaust smells rich, no not black smoke, just a strong smell.(although I dont yet have a way of measuring CO). Not sure.
3) The air plate is not against the housing. I beleive its in the correct spot for idling. It moves ok by hand, just (I think) to much pressure against it.
4) I have the Probst book on Bosch engine management systems, its been really helpful. I will keep on studying it.
5) Yes, the car has been sitting a long time (10 years?) I drained the tank, put a new fuel pump and filter, cleaned out what I could, and it fired right up. Initially it was reving ok, but since I have been running it longer, this problem has arose. Maybe residual dirt/gum in the system showing up. The reason I took on this project is the car is a Euro, and only has 40k miles, so I think it'll be nice if I can resurrect it.

Thanks
Rick

jpitman2

pROBST IS GOOD FOR THEORY OF OPERATION, imho WATSON is better for diagnosis. Do the above tests for blockage, working from outlet (return) from WUR back to distributor to isolate the blockage. High system will give a bit rich, high control will prevent extra fuel with extra air. Some people try to clear old crud by bridging fuel pump relay, adding techron or similar to fuel, and just letting the fuel circulate around and around to try to flush the system. If you isolate the blockage to the wur, do a search for a document I wrote with pics of internals of WUR. If remove wur, you will find fine gauze filters in there that may be blocked with crud. If you have access to compressed air, maybe you could blow the crud out CAREFULLY. I cleaned mine out some by pushing carb cleaner BACK through it with a syringe. If you removed the electrical parts you could soak it in a solvent?
jp 83 Euro S AT 50k

SMTCapeCod

OK, I'm rusty again. Why aren't we thinking sticking/inop system pressure regulator @ the FD?

928FIXER

Check to see if it has a add on DOT fuel control kit for EPA regulations for importation.If you have it,it needs to work or be taken off before checking fuel control pressures and even if it works it can make for some funny control pressures at times.

Don Carter

I was going to mention the filters in the WUR. I think a lot of people just remove them as I did.

Sounds like you are working through similar issues as I am with my euro that's been sitting 10+ years. I tried carb cleaner in the fuel distributor but it's no better. Recently the tank started leaking so I put something to catch the gas. When I sucked the leaked gas into a glass jar a few days ago, I was amazed that the gas was a black as coffee, and it was riding on top of an inch or so of WATER!!!

That's the problem with moving so slowly on a project, I have in my mind that I did drain and clean the tank, but in reality that was like five or six years ago. Time to do it again.

Eric Vaas

Grendl,
I have the pressure regulator out, and its clean. The only two things I have fooled around with are replacing the pump, and taking the WUR apart. Perhaps the newer pump I got is putting out the wrong pressure, and/or maybe I assembled the WUR incorrectly (or it doesn't work right!); I couldn't see anything wrong with it at that time. I suspect the WUR. I'll check it this weekend. The checks for return blockage sound like a great thing to do also. I'm away from the computer this weekend, so thanks for the help to everybody.
Rick

jpitman2

Rick, the pump, as long as its meant for injection, should be ok if its new. Mine had an S4 pump on it for years, worked fine. Pumps deliver volume, pressure regulators control pressure. Remove the WUR filters, check pressure again. High control will stop the plate moving and give the symptom you have.
Here is a link to my doc on WUR..
www.landsharkoz.com/images/pdf/wurfix.pdf
jp 83 Euro S AT 50k

928BC

JP's WUR doc. rules!!