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> Diagnosing an intermittent D-Jet problem..., Hesitation under load at 2800 RPM but only when cold...
MikeInMunich
post Oct 10 2016, 02:46 AM
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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
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pbanders
post Dec 7 2016, 08:07 AM
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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.
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MikeInMunich   Diagnosing an intermittent D-Jet problem...   Oct 10 2016, 02:46 AM
The Cabinetmaker   First suspect would be the tps adjustment. Usually...   Oct 10 2016, 09:54 AM
MikeInMunich   Hmmm. A mechanic had checked that here just a few ...   Oct 10 2016, 10:18 AM
MikeInMunich   First suspect would be the tps adjustment. Usuall...   Dec 7 2016, 01:27 AM
RobW   Dads car had the same kind of RPM hesitation back ...   Oct 10 2016, 10:02 AM
MikeInMunich   Thanks, I'll check that out. Good tip.   Oct 10 2016, 10:16 AM
MikeInMunich   :beer2:   Oct 10 2016, 10:17 AM
914_teener   Mike..... Here would be my thoughts and in this o...   Oct 10 2016, 11:52 AM
MikeInMunich   Mike..... Here would be my thoughts and in this ...   Oct 10 2016, 01:07 PM
MikeInMunich   Mike..... Here would be my thoughts and in this ...   Oct 11 2016, 12:01 AM
914_teener   mark at 914 rubber sells the boards...IIRC That.s...   Oct 10 2016, 01:10 PM
MikeInMunich   mark at 914 rubber sells the boards...IIRC That....   Oct 10 2016, 01:14 PM
pbanders   Hi again from Munich! Here are the details. ...   Oct 10 2016, 02:18 PM
socal1200r   We just had a discussion among us so-called ...   Oct 11 2016, 11:04 AM
Dave_Darling   Worth double-checking all the electrical connectio...   Oct 10 2016, 04:54 PM
mepstein   Worth double-checking all the electrical connecti...   Dec 7 2016, 09:12 AM
BeatNavy   First of all, I agree with DD - check your electri...   Oct 11 2016, 04:03 AM
MikeInMunich   Checked the CHTS connection...seemed to be OK, BUT...   Oct 11 2016, 09:28 AM
BeatNavy   Checked the CHTS connection...seemed to be OK, BU...   Oct 11 2016, 10:56 AM
MikeInMunich   I don't think that had anything to do with th...   Oct 11 2016, 11:30 AM
BeatNavy   There's a hole in the engine tin next where th...   Oct 11 2016, 11:11 AM
MikeInMunich   Tested CHTS, <300 Ohms when warm. Approx. 2000 ...   Oct 13 2016, 01:10 AM
MikeInMunich   Is this a clue? Driving this evening, with a fault...   Oct 13 2016, 11:33 AM
pbanders   Still sounds like an intermittent contact issue. ...   Dec 7 2016, 08:07 AM
StratPlayer   I was having that problem,,,hesitation,,,,, I just...   Dec 8 2016, 11:21 AM
MikeInMunich   I was having that problem,,,hesitation,,,,, I jus...   Dec 9 2016, 02:23 AM
pbanders   More ignition checks: Verify that your vacuum adva...   Dec 8 2016, 07:10 PM
MikeInMunich   Hi Brad, thanks for all your advice. I will be loo...   Dec 9 2016, 02:27 AM
socal1200r   Hi Brad, thanks for all your advice. I will be lo...   Dec 9 2016, 06:04 AM
Matty900   Gary Cotton did 2 great videos on this. Part 1 htt...   Dec 9 2016, 08:20 AM
MikeInMunich   Thanks again guys! Huge help!! Have a...   Dec 9 2016, 08:45 AM
MikeInMunich   Update, edited! Unfortunately I don't tru...   Feb 5 2017, 12:55 PM
Bob L.   Update, edited! ... Also, when the engine is...   Feb 15 2017, 09:41 AM
Jeff Bowlsby   The ECU knob is a fine adjustment to fuel mixture ...   Feb 15 2017, 09:50 AM
MikeInMunich   :bump: Seeking expert's feedback on D Jet Prob...   Feb 14 2017, 01:58 PM
914_teener   So did you do everything Brad noted? I would sugg...   Feb 14 2017, 02:38 PM
MikeInMunich   So did you do everything Brad noted? I would sug...   Feb 14 2017, 03:28 PM
914_teener   So did you do everything Brad noted? I would su...   Feb 14 2017, 04:01 PM
MikeInMunich   If you have checked everything he posted........i...   Feb 15 2017, 01:36 AM
MikeInMunich   Update: Disconnected the TPS today and tested...Pr...   Feb 15 2017, 01:50 AM
Dave_Darling   The "AT idle" is determined by the idle ...   Feb 15 2017, 02:09 PM
MikeInMunich   Hi Dave, thanks for chiming in again here. I...   Feb 15 2017, 05:23 PM
914_teener   Shiza Mike! That is an important detail. Gues...   Feb 15 2017, 09:45 PM
MikeInMunich   Update!! Interesting "insight"? ...   Apr 2 2017, 04:08 AM
MikeInMunich   Problem solved, it was the air temp sensor! A...   Jun 25 2017, 03:30 AM


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