'87 Jetta GLI 16V - progress

OK guys, here's where I'm at now with this (formerly) dead VW:

After going through everything from air cleaner to intake, repairing what little I could find wrong, replacing all suspect vac hoses, and fixing one vacuum leak, I got it where I could drive it - barely. It's obviously running way lean, because once I get the throttle into the WOT enrichment, it wakes up immediately. I know the rice-rocket shop turned the fuel distributor adjustment screw a bunch, not knowing what they were doing. My question is, does that have an effect on the basic running mixture (as opposed to idle only)? Can I expect to crank the 3mm adjustment screw a little at a time and bring the mixture into a drivable range? I know the correct way to do this is with an ammeter reading the o2 sensor circuit, but the o2 sensor does not get hot enough to operate for this purpose. Remember this is a race car, and most people racing these effectively bypass the o2 sensor and treat it as a straight CIS system.

Reply to
Rex B
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Try turning the CO adjustment screw for best idle and see what that does. Then turning that screw out (CCW) should lean the CO and the engine should become more responsive. Adjusting that screw should have an effect on off-idle response too AFAIK.

Do you have a CO analyzer at your shop? Do you analyzer how rich the engine is running by examining the spark plugs at different times, like after a WOT run then turning the engine off to see what color the spark plug tips are, or after a cruise down the expressway, etc.?

You can, or should be able to, hook your VOM in series up to the Fuel Pressure Regulator to read it's voltage.

Good luck, dave (One out of many daves)

Reply to
dave

This is the 3mm screw below the hole by the fuel distributor, right? So screwing it in (CW) should richen the mixture?

No.

I do read the plugs occasionally, but it hasn't run well enough so far. I'm in the "rough" tuning stage now.

I was told by a VW tech that the O2 sensor wasn't getting hot enough to do that, due to a convertor whose guts were gone. O2 sensor is in the cat convertor shell, shielded from direct exhaust flow. So I haven't done that.

Reply to
Rex B

It should.

Your 02 sensor should be a heated one and come online within a few minutes of the engine running. Also I like to check the FPR voltage to make sure that there is some and also that it changes.

Reply to
One out of many daves

So the internal heater should be able to get the sensor into the working range, without benefit of a blast of exhaust heat?

Is that a standard test? That's the rectangular box on the side of the FD, correct?

Rex

Reply to
Rex B

yes at least initially, but exhaust should be hitting even with a gutted cat. I am not totally sure on this since I only deal with 'working' & complete cats.

Should be in the Bentley.

Reply to
dave AKA vwdoc1

How dull :) Actually, the O2 sensor on this car (and I assume other Mk2s) is placed in the shell of the convertor. The bung is in the angled taper (the lower \ in the ascii art below) section such that it sits outside of the main flow, angled back toward the catalyst core. In that position I expect it would get a good portion of the heat as radiant from the hot core. That core is gone, the exhaust flow alone is not optimal from a heat standpoint. ____

----/ \------

----\____/------

Reply to
Rex B

I have seen some cats that have lost their guts through the exhaust but the engines were still running fine with the 02 sensor online. I have also seen many 02 sensors installed in exhaust pipes, so they are not in the exhaust manifold nor cat.

Just try yours and see. ;-)

Reply to
dave AKA vwdoc1

The tech told me his milliammeter would not come up into the working range because the O2 sensor was not getting hot enough, so it needed a new cat before he could tune it. But honestly I did not try it myself, nor did I verify that the heater circuit was working. I will do that, thanks

Rex

Reply to
Rex B

Well that is a possibility, but I would have to see that myself. You can plug into the FPR, jump the fuel pump relay, turn the ign. on and read the current without the engine being on. At least that is what I remember and I usually do this to vehicles that don't start. :-) Remember that I am NOT plugging into the 02 sensor but the Fuel Pressure Regulator wiring.

good luck, dave

Reply to
dave

I guess you use that standard test harness that you use to check millamps through the FPR?

Reply to
Rex B

I adjusted the mixture screw last night until I could blip the throttle without it trying to die. Then I drove it around the neighborhood a bit, and it seemed to drive pretty well, although it was not perfect. Once it got over about 5000 at WOT it really came alive, something it has not done well since I've owned it. It may be still too lean, and it has that odd smell that I used to associate with incorrect ignition timing. Additional tuning is indicated, but I am going to try and leave that for the next owner. Thanks much to Dave and others for your help.

- - Rex Burkheimer WM Automotive Fort Worth TX

Rex B wrote:

Reply to
Rex B

yeah I build up something from some spare plugs off of another wiring harness.

Reply to
dave AKA vwdoc1

Followup. OK, the car ran well after adjusting the mixture by feel. Called the buyer, he was tickled, and drove it home (not tags, no inspection, roll cage, a little loud) to north Dallas. Called and said it wouldn't idle nor rev over 3000. Sigh. Next day he said he found a cracked plastic piece where the injectors enter the intake manifold. He is going to get all new pieces to seal the injectors today. I think he is onto something.

- - Rex Burkheimer WM Automotive Fort Worth TX

dave AKA vwdoc1 wrote:

Reply to
Rex B

BTW I have seen bad injectors do that also. It all depends on what is marginal on the car. If too many things are marginal they can all add up to a poor running vehicle. :-( Could be clogged screen on the intank fuel pump, or clogged inlet to the main fuel pump housing, or or or..........

keep us informed if the problems are found!

Reply to
dave

That's the direction I was going when it started running. Had it not run OK, ignition was next. Injector seals would have followed after that, then injectors.

I'm pretty sure fuel tank, both pumps, fuel distributor assembly throttle body are fairly correct.

- - Rex Burkheimer

dave wrote:

Reply to
Rex B

Either not enough fuel getting inside the cylinders or possibly a clogged exhaust system. I had a collasped rear muffler on my 91 Passat. It did not run well at all that way. lol

later, dave (One out of many daves)

Reply to
dave AKA vwdoc1

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