D-Jet Problems, Stalls when hot, misses at med. rpms Options

[john_g]

I'm having problems that I'm pretty sure come from somewhere in the D-jet system. I have a '74 914, bored to 2056. Here are my symptoms:

It idles okay. It's a bit rough when cold, but it doesn't cut out on me and warms up to a steady idle quickly (1200 when cool, 800-900 when warm), but when it's been run for a longer time and is good and hot, the idle drops well below 800 and it stalls. It'll start back up right away but only if I treat it as if it's flooded - I have to put the accelerator to the floor as I restart it. Secondly, at mid rpm's, between 2200 and 2800, it hesitates, sputters, misses, and occasionally backfires - this happens whether it's cold or warm.

What I've done or have had done:
usual tuning routine
replaced the CHT sensor
replaced the MPS
replaced the distributor
cleaned the PVC valve
checked for vacuum leaks
checked the TPS, it seems good

Two air-cooled mechanics with good reputations have worked on it and haven't been able to solve the problem fully. All the above helped a bit, but the situation is still there. There has to be some sensor that isn't reading the situation correctly. Any ideas, or ... has anyone had a similar problem? (IMG:style_emoticons/default/confused24.gif)

[Old Yella]

Hi
I don't usually give advice but as I have had the same shit happening I have sought advice and got some excellent advice from the forum. Thanks Tom.

Mine car now runs great when hot but has cold temp problems as some components are just worn out. I'm working on those slowly.

My car was doing exactly the same thing as yours

1 check for air leaks

2 check your fuel pressure is correct, mine went up to 70 psi. pressure regulator failed.

3 timing is critical.

4 Check the TPS with the ohm meter. I got a replacement that checked out and then it caused bucking so it was back to the old worn one which worked a bit better

5 Don't adjust anything till the motor is absolutely at operating temp

6 Try and use an fuel air ration gauge if you can because without it you may be too rich. I'm now about 6 clicks leaner and haven't broken down for weeks

7 check that your throttle plate isn't binding also, the shafts may be so worn lots of air is getting past there.

Good luck

[warrenoliver]

John,

My 73, 2.0 used to do something like what you are describing. Along with a good tuneup, consider the relay board in the engine compartment. Mine had a loose connection that I could not see because it is covered with the backing material under the board. Mine would act up when it got warm and would cut out on me and at first would allow me to restart after cranking for a while. After a while, it got bad enough so I sometimes couldn't start it until it sat for a few hours and completely cooled the engine bay. The loose connection on mine was one of the fuse holders. I got a replacement one from a friend and it fixed it. Later, I scraped all of the backing material off the original board and found the loose post that was corroded.

Good luck.

[john_g]

Hi
I don't usually give advice but as I have had the same shit happening I have sought advice and got some excellent advice from the forum. Thanks Tom.

Mine car now runs great when hot but has cold temp problems as some components are just worn out. I'm working on those slowly.

My car was doing exactly the same thing as yours

1 check for air leaks

2 check your fuel pressure is correct, mine went up to 70 psi. pressure regulator failed.

3 timing is critical.

4 Check the TPS with the ohm meter. I got a replacement that checked out and then it caused bucking so it was back to the old worn one which worked a bit better

5 Don't adjust anything till the motor is absolutely at operating temp

6 Try and use an fuel air ration gauge if you can because without it you may be too rich. I'm now about 6 clicks leaner and haven't broken down for weeks

7 check that your throttle plate isn't binding also, the shafts may be so worn lots of air is getting past there.

Good luck

Thanks for the advice. Some of the checks you've mentioned have been done, but not others, so I've got somewhere to go.

[john_g]

John,

My 73, 2.0 used to do something like what you are describing. Along with a good tuneup, consider the relay board in the engine compartment. Mine had a loose connection that I could not see because it is covered with the backing material under the board. Mine would act up when it got warm and would cut out on me and at first would allow me to restart after cranking for a while. After a while, it got bad enough so I sometimes couldn't start it until it sat for a few hours and completely cooled the engine bay. The loose connection on mine was one of the fuse holders. I got a replacement one from a friend and it fixed it. Later, I scraped all of the backing material off the original board and found the loose post that was corroded.

Good luck.

Thanks. I've already replaced the relay board, albeit with a used one, so that may still be a problem.

[boxsterfan]

Everything you ever wanted to know about d-jet.

http://members.rennlist.com/pbanders/djetparts.htm

My car had trouble at idle after warm-up and I got one of these Porsche 914/4 Cylinder Head Temperature Sensor Extension (about 3rd item down). My problem was that it was running well at warm-up (idled at 1400-1600 depending on I adjusted the idle screw) but would stall as she came up to temp. Once she got warm though, I never had your stall out issues.

http://914ltd.com/store.php?c=1384303079

[Java2570]

I would absolutely make sure that your wiring harnesses are in good shape....sometimes they can have breaks or bad spots in wires and can cause all sorts of gremlins. It would be a great idea to get ohm readings with a multimeter on your CHT for cold and hot values....that way you know for sure if the CHT is working correctly for cold and warm conditions. The webpage that Boxsterfan mentioned has a ton of great D Jet info and lots of tips and tests you can use to diagnose these sorts of issues.

[john_g]

I would absolutely make sure that your wiring harnesses are in good shape....sometimes they can have breaks or bad spots in wires and can cause all sorts of gremlins. It would be a great idea to get ohm readings with a multimeter on your CHT for cold and hot values....that way you know for sure if the CHT is working correctly for cold and warm conditions. The webpage that Boxsterfan mentioned has a ton of great D Jet info and lots of tips and tests you can use to diagnose these sorts of issues.

Thanks. I"ve used Paul's D-jet site before and it has helped smooth things out to some degree.

Another thought - would a mild performance cam (ground for EFI) cause some hesitation under light throttle?

[Millerwelds]

[quote name='john_g' date='Mar 28 2015, 04:19 PM' post='2166699']
[quote name='Java2570' post='2166659' date='Mar 28 2015, 02:15 PM']

Another thought - would a mild performance cam (ground for EFI) cause some hesitation under light throttle?
[/quote]

Webcam 73? Mine acts the same way. The bucking was cured by redoing the TPS. The low idle/stall when hot I still have to deal with.

[TheCabinetmaker]

The plot thickens. Non stock cam changes everything. Have you retuned the mps?

[john_g]

The plot thickens. Non stock cam changes everything. Have you retuned the mps?

I didn't do the tuning of the MPS, but the rebuilder did (or so he says).