16v cis motronic low on power.

[zracer22]

I've been chasing this power issue for a while.

Here's the symptoms. In first and second gear, there is no problem...the car pulls hard and quick right up to 7000 RPM. In third gear it starts to faulter around 6000 rpm, and in fourth gear it is a dog anywhere above 5000 rpm.

This screams "not enough fuel". Here's what I've checked.
Fuel filter: it was fine, but I replaced it anyway.
In tank pump: working fine.
In line pump: Pegs my 100 psi fuel gauge when not running and holds at 95 psi while car is running.

I'm almost convinced that the problem lies within the fuel dizzy assembly. Should I mess around checking or testing, or just replace it all? Is there a rebuild or cleaning procedure for it?
Thanks in advance for your help, Mark

[msogren]

You may want to check the actual timing at 4000 and above. Sometimes the knock sensor might not work and the timing goes way too far. The symptoms are the same as you state.
Check the knock sensor , by tapping with a small hammer, next to the sensor, while watching the timing light, on the mark. You can watch at the cam wheel also. The timing mark should move, as you tap the block. The 16v dont like a ton of lead, IMHO. about 26 or 28 total at 5000 and above. That is about 8* at idle, all hooked up. Some of the race cars cant run the vacuum line to the knock box. The timing goes too far. I dont know why, some computers are ok with the vacuum on and some are not. Both of my race cars have no vac line hooked up, to keep the timing less than34*( 8V)
The pressure sounds a little high @ 90#. Most of mine read about 82+-3 , running, measured at the fuel inlet, (with a fuel pump check valve fitting). Do the plugs all look black??
I am sure that you have checked all of the easy things, like exhaust, cam timing, etc. MM
Also change out the the control pressure reg, if all else checks out.

[Lael Cleland]

my vote is knock sensor....

[shwah]

Run fixed timing, and see if it's better. Then you will know.

[zracer22]

The knock sensors are brand new and there is no knock box, it's motronic. Would the aluminum knock sensor insulators help? Is it possible that I have the wrong knock sensors, are there different ones for different years of VWs? maybe I was sent the wrong ones?

[msogren]

Unplug the knockers to To set the timing at a steady #. It may start hard . MM
I would try it without the vac line and the dist turned back some.

[zracer22]

There is no vacuum line to unplug, Motronic doesn't use one. Can the timing in motronic be set at a fixed setting?

[shwah]

could jumper from hall sensor to ignition module. will have to reset timing - it will be way advanced.

[msogren]

Unplug the knock sensors and try it.
FWIW, I have had very few bad computers in over 25yrs of VW. 98 out of 100 problems are fuel delivery or temp sensors. The pressure reg is the most prone to prblems. MM

[zracer22]

Update****

Just got back from the shop. Here is what I've tested and fixed.

Fuel pressure: System, secondary and residual pressures are perfect.
New fuel filter.
On the dyno, the car runs a little on the rich side 11.0 - 12.0
A ground wire on the harness one of the Knock ground wires was broke. Fixed and tested it. Also, the parts supplkier sent me the green plug sensors for the 88-89 16v instead of the blue plug sensors for the 90-92. I didn't realize this until the other day. I'm not sure if they are different or not.
Car passed all tests listed in the bently shop book.


How's it running?
I started car, let it warm up and set timing to 6 BTDC at 1000rpm. As it rpms rise, the timing advanced to 13 or 14 BTDC, and then leveled off. There was no timing advance beyond 4500 rpm.

I swapped the chipped ECU for a stock ECU, and it was basically the same result except it leveled off around 12 BTDC.

Put back the chipped ECU and unplugged the knock sensors, and it ran exactly as it did with the knock sensors plugged in.

My next step is to ditch the 88-89 green plug sensors and get the propper 90-92 blue plug sensors.

[msogren]

Did the timing stay the same with the knock sensors unpluuged?? It should go to a low advance sweep.
The ttotal lead should be a little over 32*, unloaded(out of gear) with a timing light on the crank mark.
They seem to run the best at 28 or 29 for racing, at 4000 and over. for me
The 13 * noted is not correct, that might be the unplugged tiiming sweep.
There is a marked difference in the running , with knockers unplugged, if they work!!! If you check the timing at the cam, and you can with a twist/ advance light . The cam is half of the speed of the crank , of cours, so the timing mark has to be watched, with an advance light, and be exactly straight up.
So far, the timing is not enough. This has never occured in any of my 16v cars. most have too much advance for track work. I swap the 2.0 and the 1.8 blocks and sensors around a bit and have not noticed any real difference in the advance or the computers. The 87 is supposed to have more rpm chip tho. I do have to reset the timing some for each computer, about the same as the small ignition modules changes.
MM

[zracer22]

Did the timing stay the same with the knock sensors unpluuged?? [/b]

Yes, it made absolutely no difference if they were plugged in or not. I've ordered a pair of blue plug sensors. Hopefully it makes a difference.