Hi again from Munich!

Here are the details. But please see update from Feb. 5th below!

I have a D-Jetronic intake. Under load and at about 2800 RPM Im experiencing an intermittent hesitation. Yesterday my son and I took the car out for a drive from Munich, towards Innsbruck and back and we ran into a bit of rain coming along the Aachensee (lake), and this hesitation got worse. Then I remembered the only other time I've had this car out with 100% humidity and that it wasn't running well on that day either, so this is apparently a clue.

So what can this be? And why does it happen at all, even when it's not raining, albeit not as noticeably? Is there a cure?

Experts / senior gurus out there, thank you for your time and sharing your knowledge and experience, in advance!

With kind regards,

Mike in Munich

First suspect would be the tps adjustment. Usually causes a miss at steady cruise. Caused by a worn circuit board inside unit. Sometimes they are just dirty and need cleaning.

Dads car had the same kind of RPM hesitation back in the 80s. It was the head temp sensor on a 2.0L.

Thanks, I'll check that out. Good tip.

Hmmm. A mechanic had checked that here just a few weeks ago. Should be OK, unless it's worn, which is also a possibility. Thanks for the tip!

Mike.....

Here would be my thoughts and in this order.

Check fuel pressure.
Fuel additive to take out water from fuel.
Fuel filter or kinked fuel line
Condensation in the distributor....spray a little WD40....the wonder spray inside..clean the dizzy plate.
Bad CHT connection....check wire for nicks and or body for oxidation check values warm....ohms.
Dirty or worn TPS.

Thanks!
FP = 29 psi

Will look into CHTS and see if an additive for H2O in fuel may help. Fuel lines and filter are new, but will have a look there as well.

Seems like the TPS parts are NLA... Any info on this?

M.i.M.

mark at 914 rubber sells the boards...IIRC

That.s last on the list.

Just sent Davesprinkle a message. If he can't help, I'll get in touch with Mark. Thanks!

We just had a discussion among us so-called "D-Jet experts" as to how many of us have had a similar problem with hesitation or skipping that we eventually traced to the cylinder head temperature (CHT) sensor. The problem is caused by not getting the female spade connector (the part attached to the sensor) to correctly slide on to the male spade connector (inside the plastic housing, connected to the wiring harness). What happens instead is that the female spade connector ends up being jammed between the plastic housing and the male spade connector, and the intermittent loss of contact (due to road vibration) causes the car to hesitate or skip.

While this may not be the problem in your case, it's very easy to check and is worth doing before you go chasing other solutions.

If it's not the CHT, as others have mentioned, it might be the TPS, where the wiper track is worn and causes extra or dropped injection pulses. I'd also suggest a full evaluation of your ignition system, with special attention to the points plate. Make sure that it's moving smoothly and evenly so that your mechanical and vacuum adv/ret are working properly. Check rotor, cap, and wires. Pull the plugs and check condition and gapping. Set timing and dwell. Verify strong spark at the plugs.

Worth double-checking all the electrical connections.

--DD

Question!

When checking the resistance at the CHTS, what should it be, and sorry, but exactly where am I to connect the Ohm meter to when testing? When it's attached to the ECU, the plug isn't accessible, or is it?

Thanks!

M.i.M.

First of all, I agree with DD - check your electrical connections and your charging system. I had a very slight hiccup at 3k RPM a few weeks ago that I think was slightly faulty connections at the common ground point (3 point ground at back of case). If those are not secure, you'll get fuel delivery interruption issues.

To check the CHT do several tests in whatever order makes sense to you:

1. Visually inspect the actual connection - check the lead to make sure it's connected securely connected to the wiring harness and that the connection isn't grounding out against case or other things around it (where the lead and wiring harness connect should be protected with plastic connector). Inspect the entire length of the wiring harness to ECU to make sure it's not kinked or breaking. If the connection is intermittently open, as with a failing wire, you may get symptoms like you're describing. Keep in mind the CHT lead may be wonky at the base, where you can't see it unless you remove the whole sensor, which can be a little tricky.

2. Disconnect CHT lead at wiring harness, and with Ohmmeter, check resistance from CHT lead to ground (e.g., negative battery terminal). When engine is cold, at ambient temp (e.g., 60 degrees), you should get in the neighborhood of 1500 to >2K ohms. With engine warm, you should get around or <200 ohms (check Anders's site for more info and specs: http://members.rennlist.com/pbanders/djetparts.htm). If you don't get acceptable readings, CHT sensor is bad.

3. Reconnect the lead to wiring harness. Disconnect ECU connector (25 pole plastic connector). Check continuity from Pin 23 in connector to ground. You should get the same readings as #2 above. May want to move harness around a bit while doing this to see if you have an intermittent break in the connection somewhere.

Others may have more/better info, but again, this is a good reference: http://members.rennlist.com/pbanders/djetparts.htm

Checked the CHTS connection...seemed to be OK, BUT, after that, my idle changed upward significantly! I turned it back down with the idle screw. With the AAR shut completely the idle was over 1600 and was previously about 900. So, apparently the CHTS wasn't working and now is?? What do you think about this new symptom?

As for the "hesitation", I can at least confirm that it's not definitely still there. Seems like it MIGHT be better.

M.i.M.

I don't think that had anything to do with the CHT. It sounds like you disconnected a vacuum line in the process.

I guess you could say the CHT (and CHT "circuit") has three modes (basically): working, intermittently failing, and failed. When it's failed, or during those times when it is intermittently failing, due to a broken/breaking wire or flaky connection, the engine dies. It super-enrichens to the mixture to the point where the engine floods. If the connection is "restored" quickly enough, the car may not fully quit but "buck," I suppose, during that episode. That's it.


Wait...what?

I'm guessing CHT may not be your problem...

So where is this CHT sensor on the 1.7 engine? This sounds like a simple enough thing to check, since I have the same "bucking" symptoms at the same rpm range. I'm not driving the car anymore until I get this problem solved. Otherwise, I'll drive it to the shop and drop it off.

Thanks!

There's a hole in the engine tin next where the #3 spark plug wire goes. There's a one wire lead coming out of it. That lead is part of the CHT, although you probably can't see the sensor itself (as it's under the tin). You need a deepwell 13mm socket to get it out, and you have to bunch up the lead inside the socket.

The CHT has a profound impact on mixture to the point that if the circuit is open the engine won't start or will die almost immediately (and won't start again until cold). I can see the "bucking" thing being possible with a sketchy CHT connection, but I'm also a fan of what I think are more likely suspects, like FI grounds, ignition connections, etc., etc.

[/quote]
I don't think that had anything to do with the CHT. It sounds like you disconnected a vacuum line in the process
[/quote]

OK, apparently you must be right about the vacuum leak. I'll have a look for it tomorrow and report back. I'm starting to think the problem may be the TPS. I ordered the repair kit for it today and it'll be put in next week. I will report back results.

Thanks for your time and advice!

Mike

Tested CHTS, <300 Ohms when warm. Approx. 2000 when cool. So that seems to be working OK.

Found one hose at the pass. side of the engine on the corner of the fan shroud which had come off. Capping it didn't seem to change the idle much at all, so not sure if that was the reason why the idle had gone up so high or not.

Waiting for TPS rebuild kit from Dave Sprinkle, which will be installed next week. I'm hopeful that this will solve the issue. Will report.

Is this a clue? Driving this evening, with a faulty AAR I'm testing, while the engine was cool, the bocking was NASTY in traffic, in 1st and especially 2nd gear aroun 2400 RPM. When the engine is then warm, it runs much better, and the issue discussed here is reduced to a slight hesitation, not "bocking".

Does this tell us anything?

Thanks,

M.i.M.

I bought a new TPS plate from Dave Sprinkle, a member here. Very disappointingly, this did not relieve the symptom!

Still sounds like an intermittent contact issue.

Sounds like you've ruled the CHT out. FWIW, I contort the $#%@ out of myself when checking the CHT connection to get into the engine compartment so I can make 100% sure that the female spade connector from the CHT is actually on the male connector inside the plastic insulator from the wiring harness - it is <extremely easy> to think it's on when it's actually jammed between the plastic and the male connector. Might be worth one more check.

If it's not the CHT, I'd expand the search. First thing I'd do is find a glass-smooth section of road. Drive on it in the RPM range where you have the problem. Is the bucking still there? Now, drive on a rough section of road. Worse? An intermittent contact is suspect. If not, it's probably something else.

If you think it's an intermittent contact, check the relay board connectors. Check the underside of the relay board to make sure the epoxy coating is still in place and there's no contact corrosion. Swap in new relays on the board for the power supply (74) and the fuel pump (75). Check the ECU connector. Check all of your ignition connectors - BTW, what kind of ignition setup do you have? Check your plug wires and make sure they're in good shapee and aren't loose at the plug connectors. Check your ignition switch. Check the fuel pump connector at the pump (I had a crappy one that caused problems years ago). Check the FI grounds in the back of the engine.

What kind of shape is your wiring harness in? Most OEM harnesses I've seen have gotten pretty bad over the years. Some of the best money I ever spent on my car was buying a new harness from Jeff Bowlsby.

Other than intermittent contact, look further at your ignition. Try swapping in a new distributor cap and rotor, and new plug wires. Try swapping your coil. Make sure that the ground strap inside of the distributor for the points plate isn't broken or frayed. Check your distributor shaft wobble and make sure it hasn't become excessive. Put a timing light on the car and see if your timing mark is stable. If you have aftermarket ignition like a Pertronix, Crane, or MSD, try swapping back to conventional points, condenser, and coil to see if that's the issue.

As far as other components in the FI system, the pressure sensor is another possibility. Check my web page (sig below) for photos of the internals. It could be that at a specific part-load level it's hanging up, possibly due to contamination or to a broken component. Only way to really check this is to swap in a known good or NOS unit. Yes, the MPS is really expensive, but if you have a D-Jet car I strongly suggest that you have at least one or more spares on hand, just part of the price of owning a 40+ year-old car.

I'm sure others will have some additional suggestions. You need to be methodical and eliminate possibilities one at a time. I'm sure our various ASE certified mechanics here in the forum will tell you that's how they're trained to do it. Good luck, you will find the problem and fix it.

I was having that problem,,,hesitation,,,,, I just replaced the TPS board and the problem is solved.... No more hesitation at all.

More ignition checks: Verify that your vacuum advance on the distributor is working. If it's not connected, make sure it's plugged. If it is connected, pull off the distributor cap, take a hand vacuum pump, and pull a vacuum on the port. You should see the points plate move until the advance reaches the stop. Also check for free operation of the points plate, they're often super-grimy/gritty and won't slide against each other.

I WISH that was my result!!

Hi Brad, thanks for all your advice. I will be looking into these potential sources of the problem. Oh how sweet it would have been to have this issue disappear after changing the TPS plate! Is there anything perhaps that the mechanic could have done wrong while changing that whichwe should check on?

The distributor is electronic. Is there still a vacuum advance on it?

Thanks again for your time and assistance!

M.i.M.

I'm hoping he "set" the TPS module with an ohm meter? It's not just a matter of installing a new circuit board, the "blades" have to be set to zero across the circuit board with an ohm meter, then one mark more to be properly adjusted. There's a video either on here on or YouTube that shows how to do this properly.

Gary Cotton did 2 great videos on this.
Part 1
https://youtu.be/6x4TBwXlJu4

Part 2
https://youtu.be/J_yzQB7X4Uk

Check them out.
Hope that helps

Thanks again guys! Huge help!!

Have a great weekend!

M.i.M.

Update, edited!

Unfortunately I don't trust the guy who installed the replacement TPS plate I got from Dave Sprinkle. The hesitation still persists. Also, when the engine is cold and I turn the knob on the ECU there is NO CHANGE to the idle speed at all. According to Mr. Bowlsby's posting about the system, this is an indication that the TPS isn't functioning or isn't adjusted correctly.

As mentioned above, I measured the resistance at the CHTS connector to be > 2000 at ambient temperature (summer, ca. 25 C) and under 300 Ohms when the engine was warm.

When the hesitation is happening, under load at about 2800 RPM it doesn't persist when I take my foot off the pedal.

Another hint is that it ceases to occur all but 100% after the engine is FULLY warm.

What do you think?

Thanks,

M.i.M.

Seeking expert's feedback on D Jet Problem diagnosis...

I had posted that the problem seemed to have been solved. I was unfortunately mistaken and have edited my update in the comment above this one. Expert fedback would be much appreciated!

Thanks!

So did you do everything Brad noted?

I would suggest methodical checklist approach..

That was awesome of Brad to take the time to type up such a long list, and yes, most, though not all of those things were checked. It was quite exaustive. I'm pretty sure that it's either the TPS or a bad connection, likely at the CHTS.

Just wondering right now if anyone has a clue as to why the symptom would stop when the car is fully warm.

Thanks,

M.i.M.

If you have checked everything he posted........it should run fine.


Two things....if it is an electeical problem the symptom may be stopping because the connection heats up and the intermittent connection is no longer intermitent. Meaning copper commections have high coefficents of expansion and make better contact.

If it is fuel then....same thing....fuel atomizes better in warm air.

Have you tried upping the fuel pressure to 32 psi instead of 29?

[/quote]
If you have checked everything he posted........it should run fine.

Two things....if it is an electeical problem the symptom may be stopping because the connection heats up and the intermittent connection is no longer intermitent. Meaning copper commections have high coefficents of expansion and make better contact.

If it is fuel then....same thing....fuel atomizes better in warm air.

Have you tried upping the fuel pressure to 32 psi instead of 29?
[/quote]

I have not tried upping the fuel pressure. Thanks for the tip regarding heat and the possibility of the problem being a bad connection. If it's a bad connection I'm presuming it's most likely the CHTS connection to the harness. Not sure how warm that would get though.

Update: Disconnected the TPS today and tested...Problem was still there. So this rules out the TPS, correct?

Then I checked the CHTS connection. I'm pretty darn sure it must be good. As previously mentioned, the Ohm test on that was well within parameters, over 2000 at ambient temp and under 300 after engine running until warm.

So I guess I will now have to go through Brad's entire list after all.

M.

As far as I know, the knob on the ECU adjusts the fuel mixture not idle speed.

Mr. Bowlsby probably knows something about this that I don't.

The ECU knob is a fine adjustment to fuel mixture AT idle. It has no effect off idle.

The "AT idle" is determined by the idle contacts in the throttle position switch. If they are closed, the knob will have a small effect on the mixture. If those contacts are not closed, the knob should have no effect.

--DD

Hi Dave,

thanks for chiming in again here. I've read through Brad's work on Rennlist at least 5 times over the past few months and am at it again. I currently have FIVE AAR valves here, at least three of which I've had an employee (bike mechanic) of mine open up and clean / restore. It seems like none of them are open when cold. The car idles, somewhat roughly but not stalling, around 1000 RPM but not where it belongs, like at 1600. According to Brad on Rennlist, iirc, the extra air has no effect on the idle speed if the mixture is too lean. So my next test will be to turn the knob on the ECU all the way clockwise and see if the car 1) idles higher when cold and 2) if the hesitation is lessened.

Since the CHTS has to do with heat, resistance and mixture, and the problem is going away almost entirely when the engine is fully warm, im thinking it has to do with the mixture and the CHTS. I'm also checking tomorrow if this sensor is actually the one that belongs with the ECU I have. One of them has a Resistance of just 1100 Ohms at ambient temperature and another is well over 2000. I've got the one that's over 2k but I'm not sure at the moment if that's the one that belongs with this system.

I will continue to update until this issue is solved!

Brad, if you're reading this, thanks for all your info. Your sheet on the D Jetronic on Rennlist is legendary. By the way, this 1.7 engine was expanded to 1996 cc or whatever, just under 2ltr. The cam is stock. Ignition is electronic. Fuel pressure is 29 psi. Injectors, wires, plugs, all new. I will check the grounds and use the Ohm meter here and there and report back again.

Thanks gentlemen.

M.i.M.

Shiza Mike!

That is an important detail. Guess no one bothered to ask you what displacement you have....lol.

You better make sure that you haben all the correct components that
Brad lists on that matrix for compatability.

Update!! Interesting "insight"?

Hi Brad, D.D. Mr. Bowlsby and Co. Thanks for reading and offering feedback!

I have an electronic distributor, no points. I have done many or most of the things that Brad suggested, though not all yet.

Since my last update I discovered that the guy who rebuilt the engine and did other work on the car for me before it was sent over (back!) to Germany had forgotten(!!!) to attach a proper ground from the engine to the body! The usual strap at the back of the transmission wasn't there, nor any other. Yes, I should have noticed this much sooner. It WAS causing problems, but getting two new proper grounds installed did NOT alleviate the problem that this thread is about.

BUT alas! Here is the new and I believe interesting piece of information! Temperatures over here in Munich have been quite warm this March (2017) and the hesitation we're talking about is just EVER so slightly, if at all, happening AND when I drove home late at night the other day after a radical temperature drop to under 40 degrees F, the symptom returned! It was not really bad, but absolutely far more noticeable as with the warmer temperatures.

So, does this tell us anything somewhat definitively?

Thanks!

M.i.M.

Problem solved, it was the air temp sensor!

As the hesitation was only happening in the fall, spring and then on cool nights after warm days, it was quite evident that the problem had to do with air temperature.

Auto Atlanta has the part and mentions that a faulty air temp sensor can cause this symptom. Nobody had mentioned that this sensor could be the culprit, but George Hussey seems to have known so. Just sayin'.

Yesterday I tested the faulty sensor with an Ohm meter. Resistance at ambient temp was within spec, but after putting it in a fridge for 20 minutes the Ohm meter registered, strangely enough, nothing at all. Even Dr. D-jet over here was a bit bewildered and had never seen that before.

I can't be 100% sure until I drive my car again while the temp is under 55 degrees F, but I presume having changed out the sensor will have solved the problem.

M.i.M.


Final word, April, 2018...

Other bogging / hesitations were happening because my seemingly OK contact at the battery was sub optimal. With the volt meter sometimes fluctuating and engine subsequently bogging slightly at idle, I went back yesterday and tightened the connections firmly. This solved that problem, which may have been contributing to the problem with the slight hesitation which was occurring between 2400-2800 rpm. Despite what I had written above here, changing out the air temp sensor did not alleviate the symptom 100%, albeit oddly enough about 90-95%, seemingly. Last night it was cool and I felt the hesitation once, ever so slightly, but only while the engine was cool. After complete warm up, not at all. So there may actually be more than one culprit. I suspect that the CHT sensor may also be sub optimal / a reason for this symptom, whereby the possible solution may well be the known hack with adding resistance/ a washer or two between the sensor and head. I’m not going to do that though, since the problem seems to be just about 100% gone.