Fuel Injection --- HELP!!

M

Mark LaBarre

New member
Oh wise and knowledgeable VW guru's, please offer your kind assistance to a lowly ITC driver trying to get his new ITB Scirocco running. The patient is an 86 8 valve Scirocco. The problem is the fuel injection is not quite right. After to much time wasted, I've found the wiring diagram in the Bently for 85 and 86 Scirocco's is not the correct one for my car. After looking at the control unit plug, I've found it matches the 87 wiring diagram. So, I've tried to use that as a guide for troubleshooting. The frequency valve test plug (near the ignition coil) Shows 100% duty cycle no matter what I try to simulate. If I disconect the freq valve, I can get some reading changes that match the manual on the brown/blue wire to ground. I've tried connecting another valve (very used) with the same results. The valves ohm out to the stated specs. I'm thinking that the valves are both bad, but the wiring diagram for the test plug has got me confused. It appears that there is no electrical path from the freq valve back to the control module.

Any one? Please? Pretty Please???

Thanks,
Mark
 
Mark,

Do you have a CIS with Lambda or a CIS-E?

The CIS control receives input from the tempeture sensor which resides in underside of the coolant pipe between the #3 and #4 cylinders. Until the engine reaches tempeture the Control box will operate in a full rich cold start mode. The control also receives input from the full throttle switch, which again activates a full rich response. Finally, the control receives input from the oxy sensor which is the primary operating input. Based on what the control box receives from these inputs it controls the frequency valve "duty cycle" or fuel richness adjustment. I believe it is a one way signal to the frequency valve, the box doesn't receive any kind of "return" response from the frequency valve.

I suggest you:
1) make sure of your grounds are good
2) check the signals from the temp switch, full throttle switch and oxy sensor
3) be sure your air sensor arm/richness adjustment in the distributor isn't way out of wack (the 3 mm screw adjustment)
4) be sure the frequency valve is operating correctly
5) if all of the above check out try another jetronix oxy control box.

Most often it is a ground problem, the system is pretty simple really.
good luck
 
Originally posted by Mark LaBarre:
The problem is the fuel injection is not quite right
Click to expand...

What is wrong with the fuel injection? Is it just that the duty cycle seems to be 100%?

The duty cycle (freq valve) test terminals on my 83 Rabbit GTI are on the pass side, in the same wiring bundle as the o2 sensor wire and 5th injector sensor wire. Make sure you're using the proper wires.

Also make sure you have the multimeter hooked up correctly, some meters have different plugs on the meter for the + terminal, when testing voltage or resistance, as opposed to duty cycle or dwell. Ask me how I know.

PJ

------------------
83 Rabbit GTI - future ITB
 
The car is running really lean, sputering and hesitating etc. The freq valve duty cycle never goes below 100% at the test plug. If I disconect the freq valve and measure at the connector, I can get varying signals (when I hit the full throttle switch, disconect the OXS temp switch). With the freq valve pluged in, just 100% duty cycle. The car runs the same with the freq valve unpluged. All grounds have been double checked.

I'm begining to miss my CIS from the 80 Scirocco. No electronics.
Mark
 
A lean condition cam be very easily caused by vacuum leaks. Make sure you don't have any, and that the auxiliary air regulator is working properly by pinching the hose when the car is warmed up, if the idle changes, it's stuck open. Pull injectors to check spray, etc. basically follow troubleshooting procedures in the Bentley. Maybe ask the previous owner if he did any 'tricks' to the FI.

PJ

------------------
83 Rabbit GTI - future ITB
 
Mark,

The test plug should be showing what the signal is coming from the computer, not what the frequency valve is doing.. I don't think checking the current at the frequency valve tells you anything. I assume the valve is "buzzing" or "clicking" which means it is working.

Actually what you are saying makes a lot of sense - again I assume you are determining a lean running condition from a fuel mixture gauge running off your oxy sensor. If you are running lean of course the computer would tell the freq valve to run full rich! it is doing what it is supposed to.

Check for vacuum or air leaks as PJ mentioned and the injector spray as well. I think your problem is with the air flow sensor adjustment - if it is to lean the computer can not compensate for it and you will have a problem. Get a long handle 3 mm allen wrench and adjust the air sensor adjustment screw to increase the fuel mixture. In doing so the computer will back off the frequency valve duty cycle. It sounds like you may close to having it working correctly. good luck
 
Well, I'm just plain stuuuuupid! For whatever reason, I mistook the Bently when it said that an increasing duty cycle meant a lean condition. I thought that meant 100% duty cycle was CALLING for full lean. DOH!!!
Gonna get out the propane and start looking for Vacuum leaks tonight.
Thanks guys!

Mark
 
In case it may help some one else.
The Bently was wrong again. There were 2 connectors on the right side of the car that were SUPPOSED to be for the cruise. Once these were attached to ground, the Lambda system worked fine.

Word of warning; THe Bently manual for the 85 and up Scirocco's has MANY wiring mistakes.

Mark
 
You must log in or register to reply here.
Back
Top