2.0 fuel injection woes

[911buff]

I am at a loss. I have been working on my 2.0 fuel injection for a while now and it should run great...but it doesn't. What I have done:

* Rebuilt engine
* replaced all gaskets
* installed electronic ignition module (operating at 47 degrees of dwell)
* cleaned injection trigger points
* installed new TPS circuit board (adjusted per web site instructions)
* checked and repaired all electrical connections
* reconditioned all injectors (Witchhunter Performance)
* ignition timing set to 27 degrees BTDC at 3500 RPMs
* valve adjustment
* fuel pressure at 28 psi
* Both temperature sensors ohm out correctly, hot and cold
* MPS holds a vacuum
* MPS ohms out correctly

My dilemma; even though all should be good, there is no crisp acceleration. The TPS talks to the brain because I get 19 “accelerator” squirts at the injectors (I find it strange that as the throttle is brought back to idle, the injectors fire 19 times again. There shouldn't be “squirts” on deceleration. Right?) . However, acceleration is no better when the TPS is connected than when disconnected. And when the TPS is connected, the engine bucks and cuts out during acceleration, deceleration and constant throttle, even though the circuit board has been replaced and TPS adjusted. There seems to be no rhyme or reason as the bucking/cutting out is intermittent. Also, the engine is running a bit rich. I have followed all the troubleshooting tips on this website and on Rennlist. I can find no vacuum leaks or anything else out of the ordinary.

If anyone has any advice or an idea on what I may have missed or did wrong, please fire away. I am open to just about anything at this point, including carburetors...not really. Thanks.

[John Rogers]

In all the years we had my daughter's 1974 2L D-Jet car, we found that after replacing EVERYTHING and the engine still ran terrible, replacing the trigger points cured the problem. We never found cleaning, filling, etc, etc did anything to help them. So we finally replaced them FIRST and generally that cured any weirdness immediately.

I noted you said you cleaned the trigger points.......

[911buff]

Yes, we cleaned them. I am afraid that they are bouncing, causing the rich condition. I have not found a set for a reasonable price, though. I am trying to develop an electronic set but right now I am just in the thought process/drawings stage. I guess I Will have to procure an old fashioned set in the mean time. Thanks!

What about the TPS firing the injectors in the deceleration phase? Any ideas? Does not seem right to me.

[Dave at Pelican Parts]

They should not fire on decel. The wiper of the TPS actually has two parts to it. When the throttle is moved in the "open" direction, the inner part of the wiper should rest against one side of the outer part. That should complete the circuit as the wiper goes across the tracks. When the throttle is moved in the "close" direction, the inner part of the wiper should rest against the other side of the inner part, and be disconnected no matter where the wiper is on the tracks.

If the engine bucks with the TPS plugged in, it is suspect. New part or not--it is still suspect. It might not be the new circuit board, though--perhaps in some of the parts you did not replace?

--DD

[hardflex]

i've had luck in just bending the tabs on the trigger points to give a wider gap. You might try that. I suspect your rubbing block has worn down so there is no gap in the trigger points.

also, could the distributor rotor shaft be worn and make the car buck due to change in vacuum advance/ retard diaphram.

just a thought

[bowlsby]

The trigger points are easy to check, pull the dizzy, and check for switched continuity as the shaft is turned. They simply initiate the injection pulse.

You can test each of the FI components, assuming the engine is also in top shape mechanically and electrically. Google "Bosch VW-Porsche D-Jet Fuel Injection Manual" and you find the manual of the same name with a diagnostic process.

[911buff]

Thanks for the advice.

For the TPS, I am confused. There are three arms on my TPS, not two. Or am I not understanding your explanation? The three arms travel on three separate tracks. They seemed to sweep true as I tested it. I will check the sweep again to see how they are arranged.

For the trigger points, I can only guess that they are the original points and are completely worn out. They appear to be in good shape but I have never seen a new set, so I am unsure of how thick the blocks should be. I will try the idea spreading the contacts while I attempt to procure a new set. Can't be any worse! I had checked the continuity of the points by spinning the dizzy and they fired right on cue. I can not spin it fast enough to make them bounce. So I am just speculating that they are bouncing. Plus I have been informed that I would need an oscilloscope to diagnose that ailment accurately.

I will check back later as I have some more troubleshooting to accomplish.

[911buff]

One more question, what is the arc in degrees that the trigger points send a signal to the ECU. The ECU is getting a signal for approx 160 degrees. There is approx 20 degrees between one signal ending and the next one starting. Is this normal? Looking at the dizzy shaft, it looks right. It seems like the injectors are firing for a long time if for 160 degrees of travel. But then I am no injection-ologist. Thanks!

[911buff]

OK, I put the original TPS circuit board back in an no more pulses on the deceleration phase and no more bucking. I opened the gap at the trigger points a hair. It runs better but still lacks the acceleration I feel it should have. At one point about a year ago, it would pull very strong then all of the sudden, not so much. I found that the #9 and #20 wires at the TPS were broken...after I purchased the new circuit board. But even now there is not the acceleration that I had before. I will keep searching.

[Dave at Pelican Parts]

Originally Posted by 911buff

For the TPS, I am confused. There are three arms on my TPS, not two.

The arm that wipes across the "accelerator enrichment" tracks is actually two parts. The part of it at the pivot is not tightly connected to the actual arm, and allows it to move a little bit independently. That's what gives you the "only on acceleration" function.

Jim Thorusen did a write-up on that a number of years ago, but I cannot find it now.

--DD

[Nostril Cheese]

Sure sounds like a bad set of trigger points to me...

[911buff]

OK, so now the 2.0 is running pretty well. I have a question, how do I know if the spark is as "fat" as it should be? I am afraid the ignition is not producing the spark it should. Any thoughts?

[Tomsherman]

I agree about the trigger points (#1 problem device). I remove the distributor, then the breaker plate with the trigger points still installed. Rotate the shaft and keep eye on points. You will usually have to fine tune the opening on both sets to get them the same with ample opening. This prevents both injector misfire and double injector firing.

I also find with todays alcohol infused "gas" my car responds better with fuel pressure 30-31 psi. Runs quicker, cooler, and still gets 28 MPG city, 32 continuous highway.

Make sure you are not running too lean, just kills acceleration and drivability with d-jet.

[Dave at Pelican Parts]

You can also look for bouncing injector points with an oscilloscope, if you can get ahold of one.

--DD