2.0 16v motronic problems

[zracer22]

Here's the deal. This winter I rebuilt my 1988 GTI race car from the ground up. The engine is a 2.0 16v with Auto tech cams, euro intake, header w/ open exhaust. I also converted from CIS-E Jetronic to CIS Motronic using harness/ecu/sensors/throttle body from a 1991 Jetta and 93 Passat.

It sounds and runs great sitting in the shop. I took it to the dyno yesterday and some problems surfaced. It ran fine thru 1st, 2nd, 3rd, and into 4th but when under load running up 4th for the dyno pull it would cut in and out for a fraction of a second.(like it was shut off and back on very quickly). The dyno results were horrible. It climbed nicely to 100HP at 3500-4000 rpm, but then leveled off all the way thru 6500rpm, with a peak around 108HP. Any ideas?

I will be checking the air/fuel mixture this evening by installing a gauge.

[Eric Parham]

First of all, it doesn't sound very much like a legal IT car, so it might help you to clarify. Although 2L 16V GLIs were made/sold from 1989.5 through 1992, only 91-92 are currently classed. Thus, your 88 is a year too early to run the 2L in IT even if it did have the stock cams (and even if someone did bother to get the 89.5 and 90 model years added).

As for your problem, it could be spark, vacuum or fuel. Do you have a AFR guage? Also, since you "converted" from CIS-E to CIS-Motronic, keep in mind that almost everything in the fuel system is different even though many parts look identical. Some can be made to work but require mods or extreme adjustments, others just can't for racing purposes. Personally, I would have stuck with the CIS-E.

[shwah]

His signature indicates he is running NASA GTS challenge. Or - anything goes. He can put a 2.0tfsi in there if he wants.

It sounds like fuel to me. What did the AFR do when the issues occurred? Can you map spark timing with the dyno setup you are using as well? This might shed light on any ignition issues.

[Eric Parham]

Ah, missed that. Well, the fuel pump and injectors should be interchangeable. The fuel accumulator might not be, and I'm nearly certain that the fuel distributor won't be. The fuel distributor itself might be able to be adjusted, but it's more than just the mixture screw. Also, the fuel pressure regulator that's usually attached to the fuel distributor is different between CIS-E and CIS-Mot, and that alone could make all the difference. Oh, and make sure that the throttle body came from a manual trans donor.

[zracer22]

I'm using all of the Motronic parts; dizzy, sensors, etc...

Yesterday I hooked up a A/F meter, and it had no signal. After more searching, I found that the O2 signal wire was grounded. I ungrounded it and the meter worked fine, AND, the mixture was dead on all the way to 6500rpm. So maybe the ground was the problem all along.

[shwah]

get back on that dyno and let us know how it goes.

[msogren]

Before you get it back on the rollers, I would be able to bypass any relays that run the systems, the fuel pump, ignition, etc. Just bring some jumper wires to rule out relay flutter . A timing light , pointed at the cam wheel will show faulty timing curve / faulty crank signal. A piggy back fuel pressure guage will show dropping fuel pressure under load. A buzzy cover or exhaust could provide a bad knock sensor signal.
Grounding the O2 wire was a common"repair" for many of those cars.
It sounds like too much timing, too little fuel, restricted exhaust, something in the intake box, bad cam timing, off one link on the chain?? weak valve springs. Bad ground, coil, wires, fuel.
have fun. MM those cams arnt legal?/

[zracer22]

I just found out what caused the cutting in and out......the throttle body idle/full switch was wired backwards. The ECU thought it was idling at full throttle and wide open when idling. I'll be at the dyno on friday afternoon and then racing at beaverun Sat and Sun. I'll update on Monday

[shwah]

Good luck!