D-jet troubleshooting, Only one item left on my list! Options

[saigon71]

My 1974 2.0 D-jet is running very strong, but there were two lingering issues with the FI that I wanted to address over the winter:

1. A severe idle "hunt." The engine would rush up to about 1200 RPM, then nearly stall...repeat cycle.

2. Every once in a while the car would buck, most notably at highway speeds...it wasn't bad, just annoying.

Last week I installed a new circuit board in the TPS purchased from Dave Sprinkle a few years back. It was calibrated according to the Pelican tech article using an ohmmeter.

I took a 210 mile road trip over the weekend to test things out. The car now idles perfectly through the entire warm-up sequence. Thanks Dave! (IMG:style_emoticons/default/beerchug.gif)

The problem is that I still have the same bucking issue. All my research points to the TPS. Any suggestions on what to check next?

[watsonrx13]

I have a '74 2.0 D-jet also. My runs very well but also has a similar bucking/hesitation at 2900-3100 RPM. When I have the gas pedal set at the 3000 RPM range, then slightly reduce, it bucks/hesitate. Once past 2900 it evens out.

I have replaced the TPS circuit board from Dave, new vacuum and fuel hoses, professionally rebuilt FI. Tested TPS, MPS, new fuel pump, plugs and wires. Newly rebuilt 2056 with Raby cam kit for FI engine.

My sentiments exactly: "Every once in a while the car would buck, most notably at highway speeds...it wasn't bad, just annoying."

I too am looking for a solution to this annoying problem.

--- Rob

[DRPHIL914]

I have a '74 2.0 D-jet also. My runs very well but also has a similar bucking/hesitation at 2900-3100 RPM. When I have the gas pedal set at the 3000 RPM range, then slightly reduce, it bucks/hesitate. Once past 2900 it evens out.

I have replaced the TPS circuit board from Dave, new vacuum and fuel hoses, professionally rebuilt FI. Tested TPS, MPS, new fuel pump, plugs and wires. Newly rebuilt 2056 with Raby cam kit for FI engine.

My sentiments exactly: "Every once in a while the car would buck, most notably at highway speeds...it wasn't bad, just annoying."

I too am looking for a solution to this annoying problem.

--- Rob

try disconnecting the air intake temp sensor, see if that makes a difference.- I too had this at one time, but once i changed out the TPS circuit board, it was gone, but recently someone else had stated that in addition to a surging problem the bucking was improved by disconnecting the air temp sensor.
Logically the most obvious causes would be TPS, but if warming up partly improves it then maybe its an issue with the CHT, - just to play with this a bit, i put a potentiometer in line with the cht, and did see this clear up when i hit the right amount of resistance, also got rid of the lean running that causes idle hunting- but the real problem is either the CHT or the MPS which are not set correctly to have the proper A/F mix. ---

[brant]

I have a '74 2.0 D-jet also. My runs very well but also has a similar bucking/hesitation at 2900-3100 RPM. When I have the gas pedal set at the 3000 RPM range, then slightly reduce, it bucks/hesitate. Once past 2900 it evens out.

I have replaced the TPS circuit board from Dave, new vacuum and fuel hoses, professionally rebuilt FI. Tested TPS, MPS, new fuel pump, plugs and wires. Newly rebuilt 2056 with Raby cam kit for FI engine.

My sentiments exactly: "Every once in a while the car would buck, most notably at highway speeds...it wasn't bad, just annoying."

I too am looking for a solution to this annoying problem.

--- Rob

try disconnecting the air intake temp sensor, see if that makes a difference.- I too had this at one time, but once i changed out the TPS circuit board, it was gone, but recently someone else had stated that in addition to a surging problem the bucking was improved by disconnecting the air temp sensor.
Logically the most obvious causes would be TPS, but if warming up partly improves it then maybe its an issue with the CHT, - just to play with this a bit, i put a potentiometer in line with the cht, and did see this clear up when i hit the right amount of resistance, also got rid of the lean running that causes idle hunting- but the real problem is either the CHT or the MPS which are not set correctly to have the proper A/F mix. ---

To both of you who richened the mixture by enrich ending the cht. Did either of you verify your mixtures with a wide band? The reason I ask a that my mps is already adjusted with a wide band and I'm not going lean on the mixture. Yet I too have the exact occasional 3000-ish highway sporadic buck.

I'll try the coil and trigger points next. Not sure what is causing this

[larss]

To both of you who richened the mixture by enrich ending the cht. Did either of you verify your mixtures with a wide band? The reason I ask a that my mps is already adjusted with a wide band and I'm not going lean on the mixture. Yet I too have the exact occasional 3000-ish highway sporadic buck.

I'll try the coil and trigger points next. Not sure what is causing this

I only have a narrow band AF sensor on mine (yes I know I can't at all compare it with a wide band).
Before adding the extra resistor to the CHT the reading cycled at Optimal, after adding the Ohms it was more steady at Rich but not bottomed out. I did the adjustment during warm up since it was there the big problem was, have not yet fully checked what the reading is when fully warmed up.
I did not use the gauge to adjust - I adjusted the resistance in small steps until the cyling in rpm (almost) went out.


/Lars S



/Lars S