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

[Dave_Darling]

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

[r_towle]

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.

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

[BeatNavy]

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.

[OU8AVW]

I found this very helpful. It's not something I saw on 914 World, although it's probably somewhere in here (IMG:style_emoticons/default/biggrin.gif)

D-Jet manual

[TheCabinetmaker]

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.

[BeatNavy]

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).

[r_towle]

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.

[TheCabinetmaker]

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.

[r_towle]

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.

[BeatNavy]

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?

[ChrisFoley]

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.

[r_towle]

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...

[BeatNavy]

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. (IMG:style_emoticons/default/headbang.gif)

This evening, however, I received the new wiring harness in the mail today from Monsieur Bowlsby:


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:

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.

[Kansas 914]

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.

(IMG:style_emoticons/default/piratenanner.gif)

[Bleyseng]

Is it "Hunting" at idle? (IMG:style_emoticons/default/idea.gif)

[BeatNavy]

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?

[r_towle]

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

[BeatNavy]

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.

[Bleyseng]

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.

[BeatNavy]

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.