I had this problem shortly after I purchased my car in 2019 and I solved it with a new 2.0 914 Rubber TPS Circuit Board.

Fall 2022 I rebuild the motor to a 2056 with a mild Webcam 73 (D Jet compatable) and The Hesitation Is Back. So far I have accomplished the following using PB Anders articles and with the help of Bob D @bob164 who has logged numerous hours on this project.

-Checked the resistance of the entire engine wiring harness repairing and improving resistance on several connections. Checked all grounds. No Hesitation Fix

-Smoke tested the intake which found a leak at the Cold Start Valve, fixed. I still have a minor leak at the Throttle Body shaft and #1,2 Intake Manifold (replaced gasket and added sealant - needs resurfacing) No Hesitation Fix

-Fuel Injectors were sent to Mr Injector for cleaning and flow test during the rebuild.

-The Dizzy was disassembled-Trigger Points cleaned, Weights cleaned and lubed, Vacuum advance checked. No Fix, so I bought a 123 Blue Tooth Dizzy after reading about Trigger Points possibly being the problem. No Hesitation Fix

-The CHT sensor is within the paramaters of PB Anders data.

-The MPS checked out and did hold vacuum withing the leakdown parameters but it decided to quit holding vacuum so we rebuild it with a Tangerine Racing Kit and PB Anders data. No Hesitation Fix

-The ECU 0 280 000 037 that came with the car was replaced with ECU 0 0280 000 044. I've read that ECU's rarely fail. No Hesitation Fix

-TPS: All of the 914 World threads regaring this problem takes me back to the TPS and TPS Circuit. I now own 2 complete TPS's 0 280 120 032 and 4 circuit boards. I've tried all combinations including the 914 Rubber TPS Circuit Board and the Throttle Switch has always been set up per Ralph Ricks Instructions. I still have the Hesitation. When I disconnect the harness plug to the TPS The Hesitation Does Not Occur! The car has a little lag with the TPS harness unpluged but accelerates through all RPM's with out a problem. This test continues to lead me back to a bad or dirty TPS Board. I have cleaned and sprayed the boards and sweep fingers with electronic cleaner numerous times, perhaps the gold plated contact fingers are too warn but a continuity test as the fingers run over the track appears good. I have rechecked the TPS harness wires to the ECU and they check good.

I do not want to continue buying parts that may not fix this problem, so at this point I'm Stumped! Should I buy another Board or complete TPS or go in another direction? This is a great group with a wealth of information what do you think?

Thanks in advance,

Can you borrow a tps from a known working car? Have them put your tps on their car, see if it starts to stumble.

And just to be clear, is this at cruise or while you are accelerating? Are you wot or is this as you are actively moving the gas pedal?

"And just to be clear, is this at cruise or while you are accelerating? Are you wot or is this as you are actively moving the gas pedal?"

- This would be helpful information to have.

What parameters have you changed to compensate for the increased displacement? Bumped fuel pressure? Modified MPS?

I would like to borrow a good working TPS but that hasn't worked out so far.

Yes, this happens while cruising and accelerating. It varies from approximately 2500-3300 RPM. It does not happen if I stomp on it WOT.

The fuel pressure is set at 29 PSI and the MPS has been set with a LCR Meter back to the original settings.

Are any of the TPS parts loose? Like the drive shaft that moves the TPS? Have you aligned the TPS properly?

Both TPS's appear servicable and I have done a continuity test from the Pins through the pressure contact, through the board and through the drag switch. However there could be a problem with the sliding contacts that I can't pick up with my OHM meter. Yes the TPS has been aligned per Ralph Ricks Instructions.

Thanks

I assume you tried adjusting the advance curve on the 123, increasing it around the flat spot?

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Hi Ian, I'm still in the learning curve for the 123 Dizzy and have not adjusted it in the flat spot. I had the same problem with the stock Dizzy but willing to try different curves for the 123. I have attached my curve, I'm not using the vacuum advance. So what would you recommend?

Thanks

Lean miss? Nothing doesn't work like setting a mps by LCR. Except maybe prayer.

Do you have an AFR gauge?

No I don't have a AFR gauge but will probably weld in a bung and tune the MPS in the future. I did try a 1.7 MPS I own and had the same hesitation.

For your 73 2.0L to run correctly you really need to use matching parts as they are not identical. Recommend reinstalling the correct 037 ECU for your car.

If you need a backup 037 ECU I have one and would trade your 044 for it.

@gonzo54
having had this same issue with my 75 2.0 d-jet and i had it for a really long time until i pulled the TPS and cleaned the circuit board, my contacts had some corrosion or oxidation , i have seen some with wear patterns too, but- i used an pencil eraser and that eliminated that bucking and hesitation.
you can simply un plug it and see if that gets rid of the bad bucking if it does you know thats where the problem lies.
new circuit boards are also available, Dave Sprinkle makes them and i think 914rubber carries them.

Phil

to test the throttle position sensor, just disconnect it and see if the 3200 rpm stumble sudden cutout stops. If so it is the device, if not it is something else like grounds

Follow Jeff's advice with the ECU, also you could try to up your fuel pressure a bit. Easy to do and then check it with a wide band.

As for the 123 you don't mention if it is a switched version for D-jet or not?

If it is switched then get a matched ECU first and then use the correct setting for your engine.

The cam you have will idle a little higher then stock but....use the vacuum port on the dizzy and make sure you have ported vacuum. Ported vacuum is on the atmosphere side of the TB. Do not use manifold vacuum on the dizzy.

The symptoms you describe sound like part load advance which is what the vacuum advance is for.

That's a great cam and if the set up is right should run like a Hurricane Hilary.

Good Luck

Thanks Jeff, I will put the 037 ECU back in. I've run it with a ballast resistor and without and do not see any difference. TPS?

Hi George, I did disconnect the TPS harness:" When I disconnect the harness plug to the TPS The Hesitation Does Not Occur! The car has a little lag with the TPS harness unpluged but accelerates through all RPM's with out a problem"

Thanks,

I have the Bluetooth 123 Dizzy. Can you send me some curve numbers for the centrifugal curve and the vacuum advance (MAP)? And by ported vacuum you mean the hose above the throttle plate?

But why do I have the same hesitation with my stock Dizzy 039 905 205A? It's been disassembled, cleaned, checked and Petronix

Thanks

- because its the TPS not the distributor........

exactly what you would expect, a lag but not hesitation or bucking so , try cleaning the contacts and the board , you may see a partial or complete resolution of the issue , either get a good used board or a new board , but its very possible just cleaning the board will do it

Could still be the ECU. Different daughter card and the slight lag the part load advance.

Did you drive it like that or just manually throttle the engine? Test it under load.

Teated under load-PCH South to Newport Beach.

Just wondering if anyone might have suggestions for 123 Blue Tooth Advance Curves?

Thanks-

So...are you running a switched version of the 123? Think I posted this before. If so use the manual for the curve appropriate it's online on the 123 website. Normally the unswitched version is for L-let or carbs.

If your TPS is disconnected and your car runs without the ECU daughter card it's not set up right and playing around with the advance curve isn't the solution in my opinion.

Assure that you have the right version dizzy and switch (preprogrammed curve) and run the vaccum advance. Probably you will have to reset the static timing and reconnect the TPS.

FWIW.

They have had Bluetooth for d-jet for a couple years now.

Ok...and no vac advance? The static timing is done first. And if you don't use the vac advance then part load timing is not addressed and drivability and throttle response is compromised.

The engine and a lower rpm range under part load needs advance timing so the engine somehow needs a mechanism to address the extra advance under part load. Since there is part load at different times the curve is dynamic and not static. Most driving done is under part load.

How ya gonna do that without vac advance. Carbs have different jets under different vacuum signals but the OP doesnt have carbs.

In fact..he's said he disconnected the TPS which provides enrichment per the position of the throttle plate....and it runs fine without it? So there's enough fuel...but what about the timing? Also..I'd dyno it to make sure the mixture is good and check all the other fuel systems and valve lash.

The fact that it bogs when the TPS is plugged in could be a couple of things but I've already posted what that could be. Could be that the engine doesn't need any more fuel...and it's running too rich AND mistimed.

It is hard to figure what Hesitation means... bogging is different from a hesitation in my book. You don't need advance with a 123. Really, you don't need it period on a type 4.

Let's try and stay away from semantics and keep to engine theory of operation.

In saying you don't need it is overly broad and doesn't mention engine induction or why an engine doesn't need it.

Engine theory of operation say it's a mechanical truth...regardless of how it's achieved.

To say you don't need it on a Type 4 engine depends on a lot of things:

Induction, VE, distributor type, ect.

IE: For carbs...if you have a mechanical andvanced dizzy...maybe not. But that's not what the OP says the engine has. He posted Stock D-jet, so how is the timing for a stock D-jet engine advanced on part load?


OR..you could create a curve where at a certain RPM you've advanced the timing enough where it won't bog...hesitate or what ever it's called. But what about under 2,500 RPM where most driving happens? and what about 1,500 rpms? That becomes a dynamic situation which vacuum advance was invented and addresses.

It's just that from 74 on, d-jet didn't have advance. I don't think anyone missed it. Just another thing to not worry about when troubleshooting.

After 2 aggressive test drives I can say my Hesitation is Fixed! Turned out it was the TPS so after changing to another TPS with a different circuit board I finally got it right. I want to thank everyone that replied to this post-914 World is a great community and a wealth of knowledge.

Nice. I love happy endings.

Makes me feel so much better as I’m the one who sold him the car.

I Love This Car!
Thank you

Great news ! What was wrong with the TPS ? Seems like an uncommon problem ?

Told ya!

Seriously, though very glad it was and that you can now get back to enjoying your car!!

IMO, it's a common problem. The TPS is perhaps poorly designed. Circuit boards aren't made for this application. The copper traces are soft. Steel implants would have been better. Titanium would have been ideal. $$$. Maybe replacing it with an air flow sensor would have been best. A capacitance probe with an elliptical shaft would work. $$$$$.

There is a demonstration video on 123 Ignition USA on how to set the MAP curve. I'd set it in the middle of the two design curves. I read it last night not realizing that they had a bluetooth version for D-jet since last I installed mine years back. In any case the MAP curve handles the part load demands on timing for the engine.

Thank you, do you have a possible link to the video, I haven’t found it so far.

There is a demonstration video on 123 Ignition USA on how to set the MAP curve. I'd set it in the middle of the two design curves. I read it last night not realizing that they had a bluetooth version for D-jet since last I installed mine years back. In any case the MAP curve handles the part load demands on timing for the engine.
[/quote]

Is this the video you're referencing? Max advance seems a bit low?? at 24 degrees.

[quote name='Highland' date='Aug 28 2023, 06:04 PM' post='3098642']
There is a demonstration video on 123 Ignition USA on how to set the MAP curve. I'd set it in the middle of the two design curves. I read it last night not realizing that they had a bluetooth version for D-jet since last I installed mine years back. In any case the MAP curve handles the part load demands on timing for the engine.
[/quote]

Is this the video you're referencing? Max advance seems a bit low?? at 24 degrees.
[/quote]

Sorry, forgot the link:
https://youtu.be/238yP7Oh5Mw

[quote name='Highland' date='Aug 29 2023, 10:39 AM' post='3098789']
[quote name='Highland' date='Aug 28 2023, 06:04 PM' post='3098642']
There is a demonstration video on 123 Ignition USA on how to set the MAP curve. I'd set it in the middle of the two design curves. I read it last night not realizing that they had a bluetooth version for D-jet since last I installed mine years back. In any case the MAP curve handles the part load demands on timing for the engine.
[/quote]

Is this the video you're referencing? Max advance seems a bit low?? at 24 degrees.
[/quote]

Sorry, forgot the link:
https://youtu.be/238yP7Oh5Mw
[/quote]

Yes...unknown what engine and load profile so 24 deg at what RPM and what load. BTW...how does the dizzy know the position of the throttle plate?

Good luck.

Doesn't. If you want vacuum advance or retard some models come with a vacuum port. Other than that it simply goes off of engine rpm like a regular distributor. At least the models for the 914.

This is the 123 Ignition curve I'm running on a stock '74 2.0. I found that having some advance at idle helped low end acceleration.

Click to view attachment

Thanks @Lockwodo-the higher RPM curves are similar to mine and I will try a little more advance at 500 to 1000. It doesn't look like you are running vacuum advance (MAP Curve) are you?

No, I'm not. The 123 distributor advances in accordance with how the curve is set. And if I'm remembering correctly, my throttle body only has a retard port, not an advance port.

I should add that with 4 degrees advance at idle, the engine idles at 1000 rpm. I might be able to adjust that downwards with the throttle body air screw but it seems to be running great the way it is.

If it's MAP then it's manifold absolute pressure and not ported.

Just a suggestion...but why not call up 123 to confirm and use a MAP port on the plenum if injected so that you can utilize the function instead of using it like a 009 mechanical distributor and trying to interpolate a curve for the part load advance.

Just wondering. Most all engines have multiple sensors for just this purpose.....even dual carbed induction on these cars....if done right. There are plenty of threads here....around 2016 or 17 IIRC.

I'd be interested in looking into this. Manifold vacuum and ported vacuum are different, what is the 123 disty set up for? With the bluetooth programming you link absolute manifold pressure values to the degrees advance you want at a given kP value.

I spoke this morning with Ed at 123 Ignition. Either manifold vacuum or ported vacuum can be hooked up to the 123 disty, just a matter of personal preference, there are arguments for and against each approach. The MAP vacuum advance is in addition to whatever the RPM advance curve programming dictates. For those that would like to experiment with this, there's a "Curve Tutorial" on the website, here's the link:

https://123ignitionusa.com/curve-tutorial/

Would be great to hear comments from anyone who has tried this.