Any D-Jet topics on the board today? Anyone? No??

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
-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.

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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....

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.

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!

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).

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.

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.

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


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

Here is that image.....Click to view attachment

Ah yes, I recognize that image. Thanks.

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?

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).

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.

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

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.

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!

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)

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.

A couple of small notes: When you unplug the TPS, you take it completely out of the picture. If the problem persists, the TPS has nothing to do with it at all.

The mixture knob on the ECU is only supposed to have an effect on the engine when the TPS indicates that the throttle is closed--so basically, only an effect at idle.

--DD

so, broken record here....

At 3000 rpms and above your dizzy is at full advance and centrifugal forces will keep the plates maxed out.
As you come down into the cruise range, 2k-2500 rpms, the plates are moving back and forth quite a bit as you accel and decel....

So, if they get stuck (and they do this when hot) it starts behaving wierd.

You know how to do it...it will cost you a nickle of grease and an hour of time...

Rich

On the way home yesterday I was at a quarter tank (on 89 Octane from previous fill up) and put in 93 Octane. That definitely seemed to help, although maybe it's just masking another problem.

Last night I completely serviced the dizzy. It wasn't in bad shape, but I took it all apart and cleaned up and lightly regreased the cam, plates, etc. Put it back in and this morning I set dwell and timing right on.

It's running better, but I still feel like there's a fundamental issue somewhere. I still got some light bucking initially (when cold) and then later after it warmed up, although it was hardly noticeable then. I took the throttle body and TPS apart again, cleaned and calibrated everything, and replaced the throttle body gasket.

Again, running pretty well. I had it idling pretty nicely (still a slight hunt, so maybe I have a slight vacuum leak somewhere), but it was a little rich this time (e.g., 11.5). I slowly moved the idle knob CCW to see what it did. First couple of clicks was good (climbed to around 13 which I would guess is acceptable) but quickly went off the charts lean and wouldn't come back even after switching knob back one or two clicks the other direction. Maybe that adjustment is that sensitive, I don't know, but idle mixture is always volatile for some reason.

I should get my new FI wiring harness early next week. I'll put that on and see what happens. And keep looking for vacuum leaks.

I found this very helpful. It's not something I saw on 914 World, although it's probably somewhere in here

D-Jet manual

Have you checked to make sure the throttle plate is completely closed? A too tight cable can keep it from closing thus confusing the tps. Always leave a little slack in the cable.

I think so, Curt. Picture below is throttle body at rest, and the cable shows some slack. Very stupid question: what is the purpose of that hole in the intake (partially obscured by the throttle cable)? There's also a matching one on either side of the throttle body.

I also checked fuel pressure yesterday, and it was steady at ~30 psi. I do notice that the pressure falls immediately to zero after ignition shut off. Perhaps another question later...

I'm going to install the FI wiring harness when I get it. The only other thing I can think of at this point is maybe trigger points - I can try swapping the ones from my 1.7L into this one (I think the P/N is the same between 1.7 and 2.0).

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That hole should be a piece of tubing welded in place that goes all the way through the plenum as a structural element.

But, they do leak on occasion, so make sure the welds are still in good shape and your plenum is not rusted somewhere.

There are two tubes inside the plenum where those holes are. They are for reinforcement. It's also where the plenum is must susceptible to cracking.

Sorry to say, but the cracks or holes will be in the bottom of the plenum if there are any.
So, you need to take it out to inspect it.

In your experience is a cracked plenum a likely or possible candidate based on my symptoms, and should I bump it up on the priority list for checking?

I've seen a few cracked 2 liter plenums.
The cracks have always been on the bottom surface.

You are going to redo the wiring anyways....it's about 20-30 minutes to pull it and check it....just so you know for sure.

It would add an air leak you will never find...

But, a new harness may cure what is going on here...

To follow up on this issue, yesterday I replaced all the spark plug wires and tried to make sure they weren't causing EMI issues with the trigger points or other FI connections. I also replaced some of the vacuum lines that may have been the most suspect for a leak. No dice -- still ran like crap the last couple of days.

This evening, however, I received the new wiring harness in the mail today from Monsieur Bowlsby:
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Very nice craftsmanship. Got it installed after a bit of struggle with the ECU connector (the guide on the inside of my ECU is a little wonky) and was a bit baffled when the fuel pump wouldn't run until I realized one of the ground connections had disconnected as I was wrestling with that ECU connector. Anyway, I don't want to be "that guy" and say it's fixed one day only to come back tomorrow and say "I spoke too soon," but for now:
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Maybe the idle is a still lean, but right now the bucking is completely gone and the teener is running like a champ again, presumably due to the new harness. The upside to chasing down an issue like this is you do end up servicing/replacing multiple things that benefit you in the long run. It's also nice to have FI wires that don't snap, crackle, or pop every time you move them. Thanks for everyone's help and recommendations. Hope this one can be put to bed and stay in bed.

Is it "Hunting" at idle?

Hey Geoff - are you thinking what I'm thinking (probably not, I'm thinking about that cheeesteak I had for lunch)? Based on your emoticon you ARE thinking something.

Yes, as a matter of fact, there still is a bit of a hunt at idle. Whaddya think?

he may be thinking about how he can get his ass back out of the cold PNW and down south again..

Hunting is either lean or rich....
turn the knob now...see how it impacts.

rich

Hey Rich - well he shouldn't do it today. It's like 66 and drizzle here in NoVA today (in June!). Feels more like Seattle.

Definitely lean. That's what the A/F is telling me. From last night I cranked the knob over a couple of clicks CW and it helped a little. But I think I may be close to maxed out CW. How many clicks are there from full lean to full rich? Reminds me of the process to "zero" the M16 when I was in the Army for rifle qualifying when you had to click the site all the way over to one side and then come back halfway.

It's sunny and warm (high 60's) in Seattle.

The engine must be up to operating temp to adjust the mix for idle. I mean hot like been driven for 20 minutes and the AAR is completely closed. Then you can adjust the ECU knob for a smooth idle.
What CHT sender is in the car? What ECU is in the car? They have to match....and no vacuum leaks, valves adjusted etc.

I just hooked up the "new" CHT I purchase from Pelican last year (CHT). I think the P/N is 311-906-041-A. ECU is the 044.

Yeah, I'll keep checking for vacuum leaks. It runs and idles very well until it warms up, and then the idle starts to hunt a bit and go lean. I also took out the T1 sensor and tested it, and seems to check out.

Thanks Geoff.