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

I had a similar problem last year. Suggestion was to drop a couple dabs of oil into the cotton at the top of the disty shaft, to ensure the centrifugal weights weren't stuck.

Seemed to help, but didn't totally resolve the rare burp (usually an hour away from home, causing the blood pressure and heart rate to rise...)

I tried that a little bit ago and the same as yours it did seem like it helped some. i don't recall there being cotton in there though . I just put a few drops down the inside of the shaft

I had the same problem recently:

http://www.914world.com/bbs2/index.php?sho...cking&st=20

I found that when i changed out the MPS it fixed the problem, need to re-calibrate by spare which used to be the main MPS.

Two things to try:

1. Pull the dizzy apart and clean clean the advance weights deep inside to rid them of 50 yr old grease and the clean the advance plate.

2. Hook up a LM2 O2 setup and drive on the freeway at the speed this problem occurs. What is the AFR reading when this happens? My bet is the MPS is running at 15 to ! for your AFR and this is a Leaning out problem. Adjust the MPS to 13.7 to 1 at this "part load" operation. Reset the WOT to start at 11 to 1 .

Wow, I read this and thought Belgrade Maine, another teener close to me! Then I saw this is Belgrade Serbia! Wow, must be the only 914 in a 500m radius, great advice!

Nah, I am back in Seattle and didn't bother to change my location. I was going back in 15 days but cancelled the trip.

If the MPS is stock to your car and it hasn't ever been opened up, my money is on the distributor causing the problem.

Finding the root cause on this symptom can be tough, particularly if you don't have a wideband O2 sensor. To Bleyseng's point, it would probably show you running (or suddenly going) lean when the bucking starts. Lean meaning Air/Fuel ratio of 15 or more as he mentions.

But, it can also be ignition related (dizzy, etc.).

To break it down, the root cause can fall into one of two categories:

1. Fuel Delivery interruption, which can be caused by many things including:
a. dirty fuel filter, sock in tank, or other obstruction in lines
b. dirty or clogged injectors
c. poor ground connections on FI harness
d. bad, dirty or misaligned trigger points
e. worn TPS
f. poorly adjusted or malfunctioning MPS
g. fuel injector connections loose

etc. etc.

2. Ignition interruption
a. issues with dizzy (sticking advance), cracked rotor or cap, etc.
b. cracked or poorly connected spark plug wires

etc. etc. I'm sure I'm missing some ideas here.

You need to start methodically eliminating these off your list (you've already replaced a bunch of parts, so a lot of this list should already be checked). If you had the O2 sensor you could probably eliminate either fuel or ignition (if it goes lean, it's something on the fuel side, if not, something on the ignition side). In any event, I would check all your grounds and other FI connections to make sure they are secure.

I know it's annoying. Good luck!

I'm having the same problem with my 73 2.0 Djet. Happens around the same RPM or 55 MPH 5th gear. I've done a number of things suggested but have not replaced the TPS. MPS has not been adjusted-still sealed. Where can I purchase a replacement TPS and how hard is it to replace and calibrate?

-Rick Seal Beach

Take the black cover off the TPS and look at the traces. Are they worn to a deep groove or dirty? You can use 0000 steelwool very lightly to buff the traces. Use the TPS adjustment procedure with a volt/ohm meter to set them. Article was on Pelican Parts by Mike .

It's pretty easy to replace if you can use a hand drill and rivet tool.

Kit is available here: https://900designs-container.zoeysite.com/2...on-sensor-board

Calibration procedure here (requires ohmmeter): https://www.pelicanparts.com/techarticles/9...alibrate_20.jpg

You can test by unplugging the TPS connector. Car won't accelerate as well, but you can see if you're still having hiccups.

I replaced my tps last year so I would be less inclined to think it’s that. Got mine at 914 rubber. I noticed that my MPS didn’t have the epoxy on the back so somebody might have done some adjusting before me. I think I might put the distributor and give the advance unit a cleaning. I could understand sticking weights. Perhaps it might the sporadic ness of it. Short of testing the vacuum on the mps, anything else with it might be above my ability. Do I need to dismantle the whole distributor to clean it? Should I file and clean the trigger points while I have it apart?

Yes, carefully disassemble the dizzy as its pretty easy just take pics as you go so you know where to put stuff back. Clean clean the advance weights! I use a small brass brush to clean off the Gunk and brake cleaner. Leave the trigger points alone other than a dap of grease on the block.

Rick, I have taken mine apart and cleaned it, not too tough. I can help you clean yours to see if it solves your problem. I'm in Seal Beach also. PM if you want some help.
Bob

so im getting into cleaning the distributor and the vacuum advance plate is definitely a little gunky so it is currently soaking in solvent. I pulled the trigger points and noticed what seems like a slight oil film on the whole plate as if someone put to much oil in it.

https://i224.photobucket.com/albums/dd47/ns...zpsjw9hkdqf.jpg


Can I spray this whole plate off with electronic cleaner to get the oil off of everything?



I also had residual oil in the bottom of the distributor housing. Is this normal?

https://i224.photobucket.com/albums/dd47/ns...zpsf4abotar.jpg

I also noticed after running part numbers that my dist is out of a 73 914 model # 0 231 174 007 if that makes any difference

thanks for all of the help and I apologise if the pics dont work

nathan

yes, clean off the trigger points. Oil at the bottom of the dizzy means the O rings on the outside body is old.Change it.

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

Having been through this exact thing recently, reach to Chris and follow his advice. If your MPS can hold VACUUM (not pressure, ask me why I say this.....) then you can make a small adjustment that will clear this stammering.

My bets are MPS,

That's my bet too if everything else has been corrected. Pretty hard to adjust the MPS without a wideband setup hooked up to the car.

maybe a less than tight ground lead on the back of the block

I am assuming that these have been removed, clean to shiny and tightened and installed with dielectric grease! Yes, it's a common glitch where one is loose from being 50 years old.

[quote name='dr914@autoatlanta.com' date='Mar 16 2020, 09:42 AM' post='2794711']
maybe a less than tight ground lead on the back of the block

I would assume I get access to this from the bottom side? What side is it located on? I will also check the vacuum on the mps when I get my hands on a tester

thanks,

Nathan

George's 700 book has been extremely helpful to me when I was running down the gremlins. Ground loops are a reality and cause all sorts of trouble.

As per George, do not count them out, double-check all of the Djet grounds,

Still, my money id on the MPS........

We've recently problem solved the following: Good idle but no power above 3500 rpms. Went through all the components. Solved with a new set of trigger points. Old trigger point pick ups were too worn to work properly.

But then, the minute the engine got warm/ hot, it would just stop running. Removed the computer and the insides smelled of burnt electrical. A fellow 914world enthusiast lent us a computer and the problem was solved. Green pea is now running sweeeet!

Good luck and just go down the check lists, item by item.

There is a multi-spade (3 connectors) ground that's on the top middle part of the case toward the back. It's underneath the plenum, and it held on by a case bolt. You should make sure those are clean and the 3 FI connectors connect tightly to them. You're going to need to remove the air cleaner. I think you can access it without removing the plenum (it's underneath and behind it).

Looked at that yesterday evening and all seemed decent. Connections were a little dirty (greasy) but tight. They had been spliced into with new wires but appeared to be done right with solder and shrink tube. I will clean them up and then vacuum test the mps.

thought I would give you guys an update.

thanks for all of your help

nathan

Spliced and Done Right?

There is a reason that these wires were repaired. I cannot think of anything that would have me repairing that part of the wiring unless something very weird happened. Perhaps others here might have an idea?

The shrink tube could be hiding cold solder. Spend the time to take a look - ground loops are maddening and very difficult to identify. Mentally I have done the following to your car:

1. Take off the Connector at the ECU(commonly referred to as 'the computer')
2. referenced the wiring schematic and buzz out each of the ground wires as well as the control wires in the engine control harness
3. Shake the cable while the buzzer is buzzing, check for openings

I am not sure why there are so many ground wires that return to the ECU, but Bosch had a reason for everything.

Sorry to re-point you in this direction - very important to start with Solid Ground to build on.

So i finally got around to getting a vacuum pump and put it on the mps and at 10 in/hg for 1 minute it bleeds down to between 6-7. I repeated the test multiple times with similar results. I changed hoses as well with the same results. I also verified that the pump would hold vacuum just to make sure that wasn't the culprit. I also noticed that some previous owner drilled a nice little hole in the middle of the back screw to gain them access to the small inner screw. So my question is could this cause the symptoms that I am seeing? If so I will purchase a different mps

thanks

nathan

I have a perfectly tuned MPS and mine still stutters on occasion.
Vacuum numbers perfect.
Electoral numbers perfect.
Tuned with Innovate LM-2.

This summer I'm going to do some driving with the Innovate in the car to see if we see an AFR change with the stutter.
But first I'm going to tear down my dizzy and examine.

My .02c for this am. Heading out to patch up Jamie's car.

A failing MPS diaphragm that doesn't hold vacuum well (or at all) would normally result in a rich condition. I still think your hiccup is most likely caused by something going intermittently lean from interruption in fuel delivery (e.g., fuel pump briefly stopping, injector skipping a cycle, etc.) or a momentary interruption in ignition (e.g., no spark briefly).

FWIW, I believe the real test of a valid MPS in terms of vacuum is something like: pump it up to 15 psi, and it shouldn't leak down below 10 psi in less than a minute, and it shouldn't leak below 4 psi in less than 5 minutes. Or something like that.

Think of it this way: higher pressure (e.g., 15 psi) is associated with a closed throttle. The manifold has lots of pressure as the engine is running and pumping air, but the throttle is closed. That's an idle situation requiring less fuel. A wide open throttle has very low pressure in the manifold (e.g., 0 psi), and that relates to the need for much more fuel. Part load is somewhere in between, usually measured at 4 psi. Overrun is higher than idle psi (e.g., 18 psi) with no real requirement for fuel.

The hole in the back of the MPS is someone who was attempting to tune that MPS, probably to make it richer. That may or may not be related to the root cause of what you're experiencing.

I agree, look elsewhere for this problem.

guys I certainly appreciate all the help. I cleaned my FI ground connections up a bit and verified my fuel pressure ( right around 30), reinstalled my mps and then took it for a 30 mile spirited drive. Maybe its jut my head but It seemed like it did a fair bit better. It still had a time or 2 with slight hesitation going 75 on the interstate but overall i thought it did better. If it continues to behave like it did today i dont think its worth sinking much money or time investigating much further. I will further tinker with it and clean up things and see what comes of it.

thank you to all of you,

nathan

I would still add a little richness to the MPS, the diaphragm seems solid(GREAT) though PO was playing with it (hole in the epoxy).

Cannot remember clockwise or counter - however - Chris at Tangerine has posted previously on this topic -

Turning a quarter in either direction will lengthen/shorten the injector pulse and in turn the volume of fuel delivered per pulse.

Great to hear that the car is running smoothly at 70!

[quote name='ctc911ctc' date='Mar 22 2020, 10:37 AM' post='2796432']
I would still add a little richness to the MPS, the diaphragm seems solid(GREAT) though PO was playing with it (hole in the epoxy).

Cannot remember clockwise or counter - however - Chris at Tangerine has posted previously on this topic -

Turning a quarter in either direction will lengthen/shorten the injector pulse and in turn the volume of fuel delivered per pulse.

Great to hear that the car is running smoothly at 70!







nathan
[/quote]


i would be willing to give that a shot. In the rennlist article it mentions turing the inner screw counterclockwise to richen it up. they mentioned very small amounts. i just didn't know how sensitive turning that screw was and whether i would make it better longterm or worse without having the right calibration tools

nathan
[/quote]

If you're going to give it a shot, here's' more about the MPS than you probably ever wanted to know: https://members.rennlist.com/pbanders/manif...sure_sensor.htm

About 2/3 down there's a summary table of what adjustments do what (richer / leaner / no effect) on idle, part and full load.

I will also say:

1. This really SHOULD be done with an inductance meter, a wideband, and Chris Foley's adjustment tools that make it much easier. It is also helpful to have a stock baseline MPS to know how your inductance meter reads.

2. Make adjustments in very small increments (e.g., 1/8th to 1/4 turn).

Adjusting the mps without being able to measure the effects isn’t a great idea.

i had to come back to this because as i states before i believe you and i have the same issue and it’s the MPS- well you just tested your MPS and it failed. it should. or loose vac at all, so today i went back and retested mine and it was similar to yours, so i then opened it up and sure enough the diaphragm is torn. short story is i put in a new one and went for a test drive and no more stumble. it’s too rich so adjustment is in order. here are a couple pictures- you need to open up that MPS i bet the seal is bad at best and the copper diaphragm torn at worst.


after the rebuild and seal, here is the presssure at 5mmhg and after 5 min no loss.

what i am wondering is why it failed so soon. it was rebuilt about 2 years ago by Chris Foley while the car was there for rust repair, so this diaphragm was new then, and yet already failed.

good luck hope you figure it out. as for me i am sending one to Jeff Bowlsby to be rebuilt and calibrated, this one i am going to keep working on myself since i have a A/F meter and the Anders instructions for tuning.

http://www.914world.com/bbs2/index.php?act...=0#entry2779647