Just Aother D-Jet Bucking Question, My teener caught the bug going around Options

[BeatNavy]

Any D-Jet topics on the board today? Anyone? No?? (IMG:style_emoticons/default/unsure.gif)

My teener (2056) has the crud that seems to be contagious and going around: D-Jet bucking. It was maybe very slight a few weeks ago and last week I went ahead and replaced the TPS board. Now it is significantly worse, although it's hard to tell if it happened as a result of that or is coincidental to that. When I took the throttle body off I do think I tweaked the wiper contacts when I removed it -- the throttle swung open and closed before I knew it so it's very possible. I tried to make sure they were positioned back on there correctly after installing the new board. And it seemed to run okay for a few days after that (although the slight bucking was still there). I also have calibrated the TPS twice based on the Pelican article. Down below are pictures of the TPS and you can see the wipers and board (I think it's strange that after one week of use I already see a "track" where the arms is traversing the traces - normal?). I BELIEVE the arm contacts are where they are supposed to be at idle and through acceleration.

Additional information on the symptoms and system:

-bucking definitely more pronounced at lower RPMs or lighter throttle. It runs great then will very suddenly go super lean and buck
-idle is similar. One second it is "healthy" at say 13.5 AFR and then bounce to off the charts lean - at this point it's much more often way lean than in the "healthy" range. Idle will drop to really low levels (barely running)
-Last night I ran it with the TPS disconnected, and I honestly couldn't tell a difference in driveability - and the bucking was still there (IMG:style_emoticons/default/confused24.gif)
-tried to clean the contacts on the TPS last night with some emery paper. I thought it may have helped a little, but my wife says its still running like crap today
-MPS is recently rebuilt and tuned by member here
-Valves adjusted before engine install a few weeks back
-Timing and dwell recently checked
-Fuel system was pretty much completely overhauled a year ago (reconditioned tank, new lines, FP regulator, etc.)
-New FI wiring harness on order from J. Bowlsby (hopefully installed soon)

My Anders bible says it's probably TPS adjustment (or traces) or trigger points. I'm guessing Rich will probably tell me to clean up my distributor inside and out (which I'm sure is a good idea in any event). Other than those things, anything else I should look at based on the symptoms? Does the TPS below look like it could be a problem?

Thanks for da' help.

[Java2570]

Does your ECU mixture knob work? If it doesn't richen/lean when you turn it, your TPS is not adjusted right. I also noticed this week (I have been chasing a similar issue) that when I adjusted my TPS using the Pelican instructions, when I tightened the screws down after adjusting...it was changing the reading on my meter. I used to never check after adjusting but had left the meter hooked up and noticed that after I tightened the screws, it acted like the throttle had opened. I don't know if this relates to your TPS adjustment but it helped mine. Definitely clean up your dizzy to be sure it's not causing any binding or whatnot....

[mepstein]

Mine was really bad until I overhauled the distributor and cleaned off electrical connections. Tps had no effect. Then it ran great and never bucked again.

[BeatNavy]

Does your ECU mixture knob work? If it doesn't richen/lean when you turn it, your TPS is not adjusted right.

No, not really. I mean, I've only had the ECU with the mixture knob for a few weeks so I'm still getting used to it. My 1.7L ECU did not have one. But since you mention it, I thought MAYBE the knob was working, but last night I had the knob all the way over clockwise (that enrichens idle mixture, correct?) and still wasn't registering on the AFR at all (still way too lean). That tells me that it's not really working, like you suggest.

So am I possibly not calibrating the TPS correctly?

Thanks!

[BeatNavy]

Mine was really bad until I overhauled the distributor and cleaned off electrical connections. Tps had no effect. Then it ran great and never bucked again.

Hi Mark - cool, then that's on my "to-do" list for this weekend. Clean the dizzy and trigger points. And install the new FI harness (if it shows up by then).

[Java2570]

Since you indicated that disconnecting the TPS didn't change the bucking from happening, that would suggest it's not the TPS causing that. Sounds like a couple of things going on at once....
Could be dizzy causing bucking and TPS could still be out of adjustment a bit. I like that photo that Rich Towle posts of the position of the wipers but find it's tricky to get it just right without taking it out and doing it on the bench.

[TheCabinetmaker]

Check the three wires that plug into the trigger points. Make sure the wires are not weak or hanging by two threads at the crimp connector. Check the tightness of the connection in the plastic plug and that the plug is secure in its port. A loose contact here will give you fits.

[BeatNavy]

Could be dizzy causing bucking and TPS could still be out of adjustment a bit. I like that photo that Rich Towle posts of the position of the wipers but find it's tricky to get it just right without taking it out and doing it on the bench.

Do you have a link to that photo? That would help.

Check the three wires that plug into the trigger points. Make sure the wires are not weak or hanging by two threads at the crimp connector. Check the tightness of the connection in the plastic plug and that the plug is secure in its port. A loose contact here will give you fits.

Good idea, thanks Curt. I assume that the new FI harness would resolve that anyway, correct? Thanks.

[Java2570]

Here is that image.....

[BeatNavy]

Ah yes, I recognize that image. Thanks.

[r_towle]

Forget the TPS,and describe the bucking.
When does it happen?
Hot or cold?
Cruise or accelerating.


And, how is your distributor? Nice and clean and regreased?

[BeatNavy]

Hi Rich - bucking is definitely more pronounced and more likely under lighter load cruising, not under heavy acceleration or WOT. It generally doesn't happen until the car has been running a few minutes and starts to warm up (the richer mixtures during cold start may be masking it).

I figured you'd tell me to clean up the dizzy, so that's on my to-do list starting tonight. I do find it a bit odd, though, how the a/f mixture can look ok and then suddenly go wildly lean (was doing that a lot at idle).

[TX914]

Check the Cylinder Header Temperature sensor. I had this problem once on my 76 2.0 D-Jet... occasional bucking at light or constant load when warm, esp. around 2100 rpm.

[ChrisFoley]

I would adjust the MPS slightly richer and see if that helps.
That means backing out the center screw about 1/16 turn.

[BeatNavy]

Thanks, Chris. I'm a little hesitant to mess with that since it just came back "properly tuned" I believe.

You know, TX914 may be on to something. I actually have two CHT's -- at one point the original location was stripped and I repaired that before putting the engine back in the car. A week or two ago (before I had the repaired MPS) I think I may have switched the ECU connection over to the CHT that is in the original location that also includes one of those spacers to slow down warm up. I think I was trying to compensate for the lean condition caused by the weak/leaky MPS. I recall different ECU/CHT combos may cause issues, and that ECU was on my 1.7. It's an easy check, I can switch the lead over to the "old" CHT in the new location and check it out.

[Chris Pincetich]

I solved D-jet bucking with a TPS board replacement, reduced it by 50% (unplugging TPS helped me, but didn't completely solve it) and the other 50% was electrical connections at the battery plus old battery and alternator. I live near the coast, don't have a garage so store the 914 outside, and MUST disconnect the battery positive terminal every year to clean off corrosion and gt good metal on the battery lead. I've had it cause D-jet problems and loss of starting. I also had to tighten up the clamp holding the wires together at the terminal. This Spring, my alternator and battery slowly gave out, and once they were replaced the bucking was completely gone.

Good luck! (IMG:style_emoticons/default/beerchug.gif)

[ChrisFoley]

Thanks, Chris. I'm a little hesitant to mess with that since it just came back "properly tuned" I believe.

Bench tuning will only get it close. Final adjustment should be done in the car.

[r_towle]

Thanks, Chris. I'm a little hesitant to mess with that since it just came back "properly tuned" I believe.

Bench tuning will only get it close. Final adjustment should be done in the car.

And a resistor inline at the CHT will enrich the whole range, and may stop the sudden lean you are getting.

I use a variable POT (a volume potentiometer) wired inline on the CHT circuit.
Use a 1000 ohm POT to allow you to tune out the bucking for your needs.

When you get it right, measure the resistance across the POT, go buy a resistor that size and put it in place of the POT....Bobs your uncle.

To the Dizzy...
Think about it...the plates stick in an advances position, yet maybe you are decelerating...or you have changed from WOT to less than that.
The plates not moving because they are stuck in full advance, full retard....who knows....that just totally messes up your timing.




rich

[Bleyseng]

Thanks, Chris. I'm a little hesitant to mess with that since it just came back "properly tuned" I believe.

Bench tuning will only get it close. Final adjustment should be done in the car.

And a resistor inline at the CHT will enrich the whole range, and may stop the sudden lean you are getting.

I use a variable POT (a volume potentiometer) wired inline on the CHT circuit.
Use a 1000 ohm POT to allow you to tune out the bucking for your needs.

When you get it right, measure the resistance across the POT, go buy a resistor that size and put it in place of the POT....Bobs your uncle.

To the Dizzy...
Think about it...the plates stick in an advances position, yet maybe you are decelerating...or you have changed from WOT to less than that.
The plates not moving because they are stuck in full advance, full retard....who knows....that just totally messes up your timing.




rich

Before adjusting the MPS try to track down the lean idle issue as I'd start with the dizzy first. You can chase around in circles with this issue before check everything to make sure it's in spec and good. Adjusting the MPS richer just means masking the problem.
So it runs ok at WOT? What about at partload? (cruising at 2500-3000rpms)

[BeatNavy]

All good comments, thanks fellas. Yes, I'm going to "overhaul" the dizzy tonight. Did that on my 1.7 previously and it accelerated smoothly across the range.

Hey Geoff, It definitely runs better at WOT and above 3000 RPM. Below 3000 is where I have the most problems.