Fuel Injection issue - 84 A1 Scirocco

C

Campbell

New member
Need some help, my A1 84 Scirocco has had a dependable fuel injection system - the windage at idle has been fluid and smooth and it worked well through the rpm range.

My season has gotten off to a rough start, a new engine didn't work out so I pulled it and put the old one in. When I started it up it ran very rough and my fuel mixture gauge was black so I replaced the oxy sensor (the freq valve was buzzing). On restart the gauge worked but the fuel system was running at full rich, over 90 on the dwell meter. If I revved it to 3000 rpm it dropped to 50 cycles and worked normally. I went through the Bentley check: the water temp sensor worked fine, the oxy sensor checked out fine. I switched to my back up computer and it cycled at 50 cycles but it wasn't fluid, it would flick up a couple degrees and then flick back. When I took it to 3000 rpms it worked smoother and when it went back to idle it went to 90 cycles like the other computer did. Something has changed and it isn't clear what, any suggestions on what to check?

Again, with the engine not running but the fuel pump on all the Bentley checks were fine (inlet temp 78 cycles when jumped, 50 when not. When the oxy sensor grounded, 90 cycles, with the d battery - less than 20 cycles and the freq valve stopped) it seems with the car running, something isn't right. I am going to trace all the wires to make sure nothing has come loose. thanks
 
You need to get the fuel gauges to do differential pressure checks. That hydro-mechanical system is wholly dependent on differential pressures in the fuel distributor, and that's controlled by several factors. Without that you're pissin' in the wind... - GA
 
Check for each of the following that would put the computer into one of two open loop modes (assuming you want closed loop with a functional oxy sensor):

1) correctly wired and functional full throttle switch.

2) correctly wired and functional temperature switch.

If that doesn't help, post your computer part number(s) so we can see what they're *supposed* to do.
 
Thanks, I am going to check out the wiring tonight.. quick question, does the test port for the dwell meter give the cycles as signaled from the computer to the freq valve or the actual freq valve output? thinking I may need to swap the freq valve..

The full throttle switch was functional (when the car was running if I hit the full throttle switch the cycles would drop from 90 to 60 when released it would go back to 90, if I jumped the temp switch they would drop from 90 to 78 when unjumped it would go back to 90)

thanks
 
Hate to sound like a broken record, but you REALLY need to check your system and control pressures.

The frequency valve/O2 system was a "Band-Aid" add-on to the Bosch CIS injection system. That computer does nothing but control the frequency valve based on feedback from the O2 sensor, the temperature sensor, and the full-throttle switch (the latter two being nothing more than open/closed switches for going open loop on the freq valve). It was nothing more than a way to fine-tune the fueling in order to meet emissions regulations, and primarily at idle and partial-throttle. In fact, the CIS system will run perfectly fine without that; simply remove the computer and the car will start and run no problem; that's EXACTLY what the pre-frequency valve systems were.

However, the hydro-mechanical nature of CIS requires that system and control pressures be accurate. Simply put, the control pressure opposes and dampens the action of the fuel rod, which is itself also positioned by the flapper. Is these systems are not in good shape there is NOTHING that the frequency valve system can do to make it right.

Get the basics down before you start fighting the fine-tuning.

My WAG? Bad fuel pump, clogged fuel filter, or a bad control pressure regulator, but I certainly would not buy one without having done the basic checks in advance.

Greg
 
I have to agree w/ what Greg says, I'd also guess that it's a control pressure issue. A common practice is to relocate (and change) the full-throttle switch so that you could make the car run open loop whenever you wanted to. I've always found CIS-Lambda (CIS w/ an O2 sensor, K-Jet box, and a freq. valve) to be be more complicated than needed for a race car. For all intents and purposes, basic CIS FI is a mechanical system. The only electronic thing about it is, the thermal time switch that contorls the cold-start injector, otherwise, it's a straight hydro-mechanical setup.

As Greg said, all that stuff in there (CIS-Lambda) was there to help w/ idle and partial-throttle emmissions. Idle stabilizers, aux. air valves (which really have to be removed to comply w/ the rules), O2 (lambda) sensors, freq. valves, etc. don't do anything at all for performance, and IMHO can only introduce more potential problems.

Get a good FI test setup and go through the Bentley on how to check the control pressure. Or, you could just swap out some parts (control pressure regulator, fuel pump, fuel filter) and see if it fixes the problem.
 
Does anyone know where I can get one of those banjo adapters that you put on the fuel distributor that allows you to check the fuel pressure? I think a longer bolt comes with them too. I checked with BSI and they don't have them. thanks
 
<$60 for one is pretty cheap. I have an actual Bosch unit that I got from a garage that was going out of business, and I think he said it was like $200 or $250 when he bought it.
 
The fact that the duty cycle goes to the WOT and cold warmup setpoints when the throttle switch and temp swithes are closed pretty much shows that the lambda box is working properly. The high duty cycle w/oxs connected suggests a lean correction to a rich signal. I assume that w/oxs disconnected, it goes to 50% duty cycle.
An easy way to access/check fuel pressures on CIS is to take the apporpriate banjo bolt and braze a test point to it made of 1/4 or 5/16 steel tubing. Drill a small hole thru the head of the banjo, say 3/16, then drill part way thru w/the appropriate 1/4 or 5/16 drill from top. Stand a short tube in it and braze it up.
You can put a guage on the large control pressure regulator fitting to check control pressure which should be about 52psi hot. A common problem would be to see full system pressure due to a sticking/plugged CPR which would be consonant with your symptoms.
and ps: CIS Lamda systems don't work very well w/frequncy valve diasbled and a big rich adjustment to compensate. (they are fine w/oxs disabled)
 
I went through all the wiring and did each of the Bentley meter checks - every electrical component checked out fine. I started it up and it ran it's programmed cycles (72 while cold) and went to 50 but ran poorly. When I accelerated to 3000 rpms it worked well and cycled properly. When it went back to idle it went up to the 88 cycles... however at 3000 rpm it backs off to 50 and works fine.

I think everyone is right on that it is either the control pressure regulator or fuel pump - I have 4 spare CPR's but I want to check the fuel pressure before I change the CPR out - I am in the process of getting a fuel pressure tester now.

Thanks for your help, I will let you know how it ends up.
 
Well I finally got to check the fuel pressure tonight.. the gauge set up is pretty cool! oh well, I didn't change anything because I wanted to see if I could find the source of the issue. Of course the fuel pressures were fine, when warm the control pressure regulator pressure was 50 psi and the system pressure was 68 psi. I couldn't get the car to act like it did 2 weeks ago - it still acted "jerky" and after taking the rpms to 3000 or higher instead of going to 88 cycles when I went back to idle it stayed around 70 cycles (when I went to 3000 rpms the cycles would drop to 45 and it had the correct windage - the pressure never changed from 50psi). When I closed the valve to check the system pressure the cycles did go to 88 cycles, similar to what it did before. Tomorrow I will change the fuel filter and put on another control pressure regulator and see what it does. So far every test on every component says everything is okay -- however it isn't right.
 
1) Have you checked your fuel distributor & injectors for equal flows and decent patterns?
2) Injector o-rings for vacuum leaks (also check air-shroud port if 84-up CIS)?
3) Where is the O2 sensor mounted and how many ports does it see upstream? Is it monitoring just half an engine?
4) You could also make sure that your cold start injector isn't leaking (or getting accidently activated), which would make 1 rich (or conversely 2-4 lean).
 
Well for some reason it is different, I checked the injectors and all the connections and started it again. It actually ran fine this time till I revved it passed 3000 rpm and went it went back it stayed in the 70 cycles. The 50 psi and 68 psi fuel pressures remained constant. I guess I will swap out the CPR and the fuel filter and the cold start injector and see what it does... If that doesn't work I will swap the fuel distributor. Something has stopped working and it isn't obvious. I hate it when this happens!!!! thanks for your suggestions.
 
Well, mystery solved. When I was looking at the spare fuel distributor to put in, I noticed the fuel return hose that came off the freq valve fitting but didn't recall it on the one in the car.. apparently when I had pulled the distributor out of the way when changing engines and let it back down the return hose got crimped under the freq valve which greatly reduced its flow. I think this caused the high pressure condition I first saw (interesting as I increased revs it increased gas demand reducing fuel return and allowing things to function). The hose opened a little which caused the condition to improve on subsequent starts. After I freed it up and got it straight, everything was fine. I don't think there was any damage to the fuel distributor.

Oh well through the process I checked everything else and know everything is working okay. I really thought as you all mentioned I had a pressure issue, I just couldn't find a component not working correctly.

thanks for your help, no matter how many times you pull engines - its funny on how the little things get you!
 
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