What to do to a 2056 with 2.0 DJet, Help get this motor worked out. Options

[jk76.914]

I'm running an Isky 229 with D-Jet. Though there isn't much overlap (12 degrees at .050" lift, just like your VP228), I saw a significant reduction in vacuum at idle, though my idle was still pretty smooth and quiet. I experimented with advancing the timing at idle, and it improved significantly, which makes sense if overlap is indeed the issue. I'm in the process of modifying a spare distributor to reduce the total centrifugal advance, so I can run more advance at idle but not exceed 32 degrees (plus or minus) total at 3500 RPM. I'll know later this season.

The second thing I noticed was a lean miss at about 3000-3500 RPM at part throttle cruise. I "fixed" it by installing slightly higher flowing injectors, but I think the real solution (not proven yet!) is to tweak the MPS for richer running. Trouble is, I'm convincing myself that the problem is that the diaphram transitions off the part throttle stop too late, because if I open the throttle more (reducing the vacuum, and thereby starting the transition) the miss goes away. Unfortunately, this isn't one of the adjustments available. I hope to get a better handle on this this season as well.... There have been a number of posts from other folks having this problem as well......

I have no regrets in going with Isky.

Good luck with the engine... Jim

Wow Jim, Your the man. I've got to study up on all you said. It's over my head right now, but I'm gunna learn that stuff. Mind if I pick your brain in time? Joe (IMG:style_emoticons/default/boldblue.gif)

Sure, but it'll be a two-way exchange. I'm still putting some of this together in my own head, so I'll look forward to learning from what you're doing.

You see, I'm just a humble 914 hobbiest. I don't have all the answers, but I'm a fast learner, a pretty good engineer, and I'm not stupid. I'll warn you though- some of my ideas go against the accepted conventions around here! Makes it fun!

[Teknon]

[/quote]
Sure, but it'll be a two-way exchange. I'm still putting some of this together in my own head, so I'll look forward to learning from what you're doing.

You see, I'm just a humble 914 hobbiest. I don't have all the answers, but I'm a fast learner, a pretty good engineer, and I'm not stupid. I'll warn you though- some of my ideas go against the accepted conventions around here! Makes it fun!
[/quote]

Now thats the good OLD American way. My pleasure.

[Bleyseng]

I'm running an Isky 229 with D-Jet. Though there isn't much overlap (12 degrees at .050" lift, just like your VP228), I saw a significant reduction in vacuum at idle, though my idle was still pretty smooth and quiet. I experimented with advancing the timing at idle, and it improved significantly, which makes sense if overlap is indeed the issue. I'm in the process of modifying a spare distributor to reduce the total centrifugal advance, so I can run more advance at idle but not exceed 32 degrees (plus or minus) total at 3500 RPM. I'll know later this season.

The second thing I noticed was a lean miss at about 3000-3500 RPM at part throttle cruise. I "fixed" it by installing slightly higher flowing injectors, but I think the real solution (not proven yet!) is to tweak the MPS for richer running. Trouble is, I'm convincing myself that the problem is that the diaphram transitions off the part throttle stop too late, because if I open the throttle more (reducing the vacuum, and thereby starting the transition) the miss goes away. Unfortunately, this isn't one of the adjustments available. I hope to get a better handle on this this season as well.... There have been a number of posts from other folks having this problem as well......

I have no regrets in going with Isky.

Good luck with the engine... Jim

Its much easier to adjust the MPS for the correct AFR using the inner, outer screw and the WOT end plug. The stock injectors have plenty of fuel flow to handle it. The 2270 might be tough be still doeable depending on the cam. I have never used the Isky cams, I just know how much research was done by Raby to perfect his cam and lifter face grinds to stop the excessive wear and early death caused by the changing of the oil formula's.

[Teknon]

[quote name='Bleyseng' date='Mar 19 2007, 12:18 AM' post='876619']
[quote name='jk76.914' post='876526' date='Mar 18 2007, 09:04 PM']
I'm running an Isky 229 with D-Jet. Though there isn't much overlap (12 degrees at .050" lift, just like your VP228), I saw a significant reduction in vacuum at idle, though my idle was still pretty smooth and quiet. I experimented with advancing the timing at idle, and it improved significantly, which makes sense if overlap is indeed the issue. I'm in the process of modifying a spare distributor to reduce the total centrifugal advance, so I can run more advance at idle but not exceed 32 degrees (plus or minus) total at 3500 RPM. I'll know later this season.

The second thing I noticed was a lean miss at about 3000-3500 RPM at part throttle cruise. I "fixed" it by installing slightly higher flowing injectors, but I think the real solution (not proven yet!) is to tweak the MPS for richer running. Trouble is, I'm convincing myself that the problem is that the diaphram transitions off the part throttle stop too late, because if I open the throttle more (reducing the vacuum, and thereby starting the transition) the miss goes away. Unfortunately, this isn't one of the adjustments available. I hope to get a better handle on this this season as well.... There have been a number of posts from other folks having this problem as well......

I have no regrets in going with Isky.

Good luck with the engine... Jim
[/quote]
Its much easier to adjust the MPS for the correct AFR using the inner, outer screw and the WOT end plug. The stock injectors have plenty of fuel flow to handle it. The 2270 might be tough be still doeable depending on the cam. I have never used the Isky cams, I just know how much research was done by Raby to perfect his cam and lifter face grinds to stop the excessive wear and early death caused by the changing of the oil formula's.
[/quote]
[/quote]
Its much easier to adjust the MPS for the correct AFR using the inner, outer screw and the WOT end plug. The stock injectors have plenty of fuel flow to handle it. The 2270 might be tough be still doable depending on the cam. I have never used the Isky cams, I just know how much research was done by Raby to perfect his cam and lifter face grinds to stop the excessive wear and early death caused by the changing of the oil formula's.
[/quote]

I thought I saw a post somewhere that you have to put constant WC pressure on it turn on screw than a nut. I'll have to find that again. Sounds like lots of tool bench preparation. But worth it, if I don't fkit it up. Nice to know the adventurous geniuses out there already figured these things out.

Thanx Geoff




Do we posses the 914 or does the 914 posses us????????....LOL

[Demick]

Trouble is, I'm convincing myself that the problem is that the diaphram transitions off the part throttle stop too late, because if I open the throttle more (reducing the vacuum, and thereby starting the transition) the miss goes away. Unfortunately, this isn't one of the adjustments available.

Jim

Actually, this is exactly one of the adjustments you can make to the MPS. The stock MPS has the diaphragm come off of the part-load stop at about 6 inHg. That adjustment is set with the so-called outer screw. You can set this to a larger value to get it to start the enrichment sooner. With my 2056, I experimented with this and ended up adjusting my MPS to come off of the part-load stop at 9 inHg for earlier enrichment just like you are talking about.

Here are some posts that you might find interesting:

part 1

part 2

Demick

[Phoenix914]

(IMG:style_emoticons/default/popcorn[1].gif)

I have a 2056 with D-Jet. I know nothing about it, but am trying to be a sponge so I can get the most out of the setup.

[pbanders]

Trouble is, I'm convincing myself that the problem is that the diaphram transitions off the part throttle stop too late, because if I open the throttle more (reducing the vacuum, and thereby starting the transition) the miss goes away. Unfortunately, this isn't one of the adjustments available.

Jim

Actually, this is exactly one of the adjustments you can make to the MPS. The stock MPS has the diaphragm come off of the part-load stop at about 6 inHg. That adjustment is set with the so-called outer screw. You can set this to a larger value to get it to start the enrichment sooner. With my 2056, I experimented with this and ended up adjusting my MPS to come off of the part-load stop at 9 inHg for earlier enrichment just like you are talking about.

Here are some posts that you might find interesting:

part 1

part 2

Demick

I was just going to comment the same thing that Demick posted, that you can adjust the transition point from 6 inHg to a lower level to get the transition to full-load to come in earlier.

BTW, many of you are using the figures from my articles on the MPS, be aware that from recent testing I've done on several NOS OEM (non-rebuilt) MPS's of the same part number, that there are significant differences in the full-load mixture and transition point even within the same part number. Bosch didn't do the greatest job of calibrating these units precisely, so these numbers aren't etched in stone.

It's too bad that Porsche or Bosch never published the model-by-model calibration settings for D-Jet. I've tried to get this info from Bosch in the past to no avail....

[pbanders]

Hey, Demick, your vacuum chart in the postings you reference is great, I haven't seen that before. I'm going to be doing the same on my freshly-rebuilt motor in the near future.

[DanT]

Demick did you do all your adjustments with the MPS on the bench..?

did you do some fine tuning on the car?

I will need to do this soon. (IMG:style_emoticons/default/smile.gif)

[pbanders]

Demick, I read those postings of your tuning efforts on your 2056, you've done some good tuning. I think you'd get it better if you looked at the situation differently. Remember that D-Jet is a speed-density type of FI system. The "density" part is what the MPS is responsible for, that is, measuring the intake air density (i.e. manifold vacuum level). The "speed" part is what the trigger contact points do, which is to determine the engine speed so that the mixture can be corrected for the pumping efficiency curve (the "volumetric efficiency", or VE curve) of the particular engine.

By changing the cam and the displacement of the engine, you've changed the VE curve, and you're trying to use the "density" component, the MPS, to compensate. What you really need to do is to modify the VE circuit in the ECU to accomodate the new cam's effect. This is easier said than done - the ECU does this compensation by "OR'ing" four or five waveform generators together to achieve an overall compensation characteristic. You'd need to experiment with changing the components (resistors and capacitors) to get the desired effect - AND - you'd need to know what the effect of your new cam and displacement were on the stock VE curve to know which waveform generators to modify. The discussion on this circuit is in my ECU page.

[Demick]

Brad

I'm sure you are correct in your assessment. But modifying the ECU (or even understanding it) is wayyyyyy beyond my abilities. I am a mechanical engineer - so the MPS being a (mostly) mechanical device is something I can handle and understand.

But my motor runs beautifully with the modifications that I made, plus I get 20% better fuel economy as well. So I have no complaints.

Demick

[Demick]

Demick did you do all your adjustments with the MPS on the bench..?

did you do some fine tuning on the car?

I will need to do this soon. (IMG:style_emoticons/default/smile.gif)

Dan

I wrote this to you in another post awhile back, but I guess you didn't see it:

Dan

I can help you out with your MPS calibration. While you have some time - I would recommend getting an O2 bung welded into your exhaust (after the 4-1 collector). You'll need it to be able to install a WB O2 sensor to get the mixture correct. There are two internal and one external adjustments on the MPS. I can set one of the internal adjustments on the bench, and have a simple modification to be able to adjust the other internal adjustment externally, so that all further adjustments can be made quickly and easily with the MPS in the car (with the engine running even).

Demick

[pbanders]

Brad

I'm sure you are correct in your assessment. But modifying the ECU (or even understanding it) is wayyyyyy beyond my abilities. I am a mechanical engineer - so the MPS being a (mostly) mechanical device is something I can handle and understand.

But my motor runs beautifully with the modifications that I made, plus I get 20% better fuel economy as well. So I have no complaints.

Demick

Hey, if you're happy with how it runs, that's really all that matters! And I haven't taken on the task of modifying the speed control circuit, either. I need to look at the Megasquirt manual some time and learn more about tuning a speed-density FI system, perhaps there are some good techniques we could apply to D-Jet to cover both the MPS and speed correction tuning.