74 914 2.0 dJet slight hesitation Options

[nsargeant]

In the quest for a perfect running 914 im getting oh so close. In the past I have replaced the tps with a new one that fixed the severe bucking/hesitation. The car ran so much better after that. What I am trying to figure out now is a random hesitation/hiccup that happens mostly during steady throttle when I am cruising on a highway. If I drive 30 miles it might happen once or twice. It seems pretty minor compared to the bucking I was having with the old tps. If I recall it has had this hesitation since I have owned the car for the last 3 years. I know the distributor does have a pertronix module in it. Ive recently changed replaced a few things listed below but still have that little hiccup. What would you guys investigate next?

Replaced:
Fuel pump/filter
Installed SS lines
plugs, wires, rotor, (cap still looked new)
tps sensor

[nsargeant]

So I went through the distributor and cleaned everything, it needed it, but I still have the hesitation. I'm certain my vacuum advance is working better now though. When i did the test drive i noticed the hesitation a couple times at steady throttle just as I was going up a hill as well. I dont know if I had picked up on that before. you pick up more when you turn the radio off. It also did it at no incline as well. It seemed to be more prevalent when it encountered more of a load at steady throttle though. Another thing I noticed was the throttle transitions weren't always smooth. For instance if i coasted down to 60 and then back up to 70 repeatedly. I have replaced the tps last year but I can look into that again. I will look into the grounds for the fuel injection harness next and then check vacuum and resistance on the mps.

nathan

[DRPHIL914]

So I went through the distributor and cleaned everything, it needed it, but I still have the hesitation. I'm certain my vacuum advance is working better now though. When i did the test drive i noticed the hesitation a couple times at steady throttle just as I was going up a hill as well. I dont know if I had picked up on that before. you pick up more when you turn the radio off. It also did it at no incline as well. It seemed to be more prevalent when it encountered more of a load at steady throttle though. Another thing I noticed was the throttle transitions weren't always smooth. For instance if i coasted down to 60 and then back up to 70 repeatedly. I have replaced the tps last year but I can look into that again. I will look into the grounds for the fuel injection harness next and then check vacuum and resistance on the mps.

nathan

hey there I've been contemplating this as I read your post, and thought i'd share a few thoughts since I have had this issue with my d-jet as well for ever.
here is what I have done with no elimination of the issue-
after rebuilding and calibrating an MPS , 2 actually , I switched out the TPS board and it did improve after that but still get a bucking some times at light cruising like at about 2800-3k rpm , never at idle and never on hard acceleration. I also have a 123igintion distributor installed last year, and I have no vac leaks, injectors are tested as perfect , ess new everything except the rebuilt MPS from a few years back and the TPS board was a Dave Sprinkle one I put in probably 5 years ago.

with all that I am leaning toward either the TPS circuit not being right OR the MPS.

here is one other bit of information that is interesting, I also have observed that my A/F meter does jump when this happens, so the mix is suddenly changing for what ever reason . I think it drops, like suddenly rich for a spit second, which kind of rules out a short or ground issue because if that were the case it would go lean right?
all my grounds are rechecked and my ignition harness and other wiring for FI and motor are all less than 5 years old so ess new.

anyone have a thought on this? id like to test another MPS, and I am thinking about sending this one out to be rechecked and calibrated by Jeff B. It has new diaphragm etc in it by Chris Foley and was set by them when the car was up there 2 years ago for rust repair, and my other one I had to adjust because it was set to factory spec but was WAY lean according to my A/F but also plugs and temps confirmed too lean.
- also wondering if decel valve is part of issue because I seem to remember not having this issue before I installed the d-cell last year, and I did this when I reinstalled the motor and put in the 123ignition distributor, as I was told this would protect the MPS from getting back pressure and killing the MPS.

any ideas from others?

t\what I am saying is while you should check all this stuff, I dotn think the actual problem for you or me is the distributor or a vac leak. yes eliminate those as issues, but we have something else going on that causes this on the D-jet and its been discussed many times on other threads but I don't remember anyone every getting to the bottom of it.

Phil