Stuttering under acceleration when warm

[bueller]

You can use engine vacuum to run your test. You can make a T with a hose on the intake manifold or probably just use the ignition distributor advance hose (warm engine and not at idle).

Completed the test on the Vacuum Delay Valve and that tested out okay also. Dropped to just right below 1.2 bar mark and then slowly made it's way back to 3.4 bar.

Back to waiting for the USPS to get those shims to me.

Thanks!

[NckT]

In the meantime double check the ignition advance timing, especial the static mechanical advance vs engine speed and compare that to the manual. Is not unknown for an advance spring on a bob weight to come off and the timing gets too far advanced giving the engine the stuttering or pinking noise.

Also check that the vacuum pipes operates correct and that the ignition advance solenoid operates correct and had the vac pipes in the correct way around to the diagram and that the vacuum source is correct as in the thermo vac switch operates fine.

I'll assume you've checked the high tension leads and distributor cap/ rotor am, coil voltage etc

Good luck

[Soundkillr]

Thermo vacuum switch was bad on my car. Ran great cold but once warm had hesitation off idle up to 2k. You shouldn't have vacuum at the wur once warm. If you do, that could be your problem.

[bueller]

I just checked base timing and it was a bit off -- roughly around 10 so I adjusted that to be 13 dead on (that distributor nut is a PITA). With the help of my oldest child, I also tested the mechanical advance. Since that moved the mark off the gauge a bit, I had to guesstimate, but it looks to be accurate for both 2000 and 3000 rpm but didn't try 4000 because my child's patience was running thin by then

While I didn't test the vacuum advance specifically I did accidentally leave the vacuum hooked up the first couple of times I tried to test mechanical advance and it does look like the extra vacuum did make a bit of difference in the advance, but I don't have the proper tools to test that fully at the various vacuum levels.

For the vacuum lines, I found this article over on the UK forum by NickT/Admin-Bloke (http://www.deloreaneurotec.uk/viewtopic.php?f=17&t=4619) and per these tests, my thermo vac switch appears to be working correctly and the proper hoses go to the proper locations.

As far as the other items, I did recently install new plugs, plug wires, distributor cap, rotor, and a new coil. I've checked at night to see if there were any issues with the wires sparking and didn't see any sparks so I believe these new pieces are working as expected.

Let me know if there's anything I'm missing.

Thank you!

[NckT]

........

For the vacuum lines, I found this article over on the UK forum by NickT/Admin-Bloke (http://www.deloreaneurotec.uk/viewtopic.php?f=17&t=4619) ......
.

Thank you!

Admin-bloke is me

[NckT]

Admin-bloke is me

Oops, I said that already in Post No.10.

I've copied the test text here from the link in case moderators here don't allow back links etc.
http://www.deloreaneurotec.uk/viewtopic.php?f=17&t=4619

Vac pipes Vac pipes... the bain of DeLorean engines...
Incorrectly connected make the car run a bit rubbish......

To save time stripping the inlet manifold off and to save time, you can do the following to check that the vac pipes are connected the correct way around. There are 3 vacuum pipes come from the thermo-vacuum switch from under the inlet manofold.
1 to the T Piece on the Control Pressure Regulator
1 to the Distributor Solenoid (located between the Fuel Distributor and the fibreflass firewall/ bulkhead)
1 to the Inlet Manifold, on a small pipe stud on the Inlet Manifold nearest to the ceramic resistors

With a COLD enginer (i.e. one that has been left overnight), Blow down the pipes separately.
2 of the vacuum pipes should flow air through each other the other one feels blocked.
Label the blocked one as "Distributor Solenoid"

Run the engine until it is at normal running temperature ie coolant temp is +80c

You should be able to blow down the one marked distributor and out of one of the other pipes. Label this pipe "inlet manifold".
If you blow down the 3rd pipe it should feel blocked. Label this as the "Control Pressure Regulator".

Let the engine cool down (i.e. leave it left overnight),

Verification Test:

With a COLD enginer (i.e. one that has been left overnight),
Blow through the vacuum pipe labelled "Inlet manifold", Air should come out of the vacuum pipe labelled "Control Pressure Regulator".
The remaining vacuum pipe labelled "Distributor Solenoid" should be blocked.

Run the engine until it is at running temperature.
Blow through the vacuum pipe labelled "Inlet manifold", Air should come out of the vacuum pipe labelled "Distributor Solenoid"
The remaining vacuum pipe labelled "Control Pressure Regulator" should be blocked.

If your vacuum pipes pass the above test, connect them up, noting that the vacuum pipe from under the inlet manifold marked "Distributor Solenoid" connects to the CENTRAL Vacuum stub on the Distributor Solenoid. This too is also handed and affects the way the engine runs.

If test is NOT OK then but always follows the engine hot test, chances are your thermo vac switch is stuck in the "HOT" position.
Before you replace this, check that you are actually checking the correct vac pipes from under the inlet manifold.
I have noted on one car that the pipe from under the inlet manifold was actually connected to the hot water valve vacuum connection!

Enjoy !

Admin-bloke

Admin-bloke, "The D Whisperer"
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[David T]

There was a Service Bulletin covering how to check for proper vacuum hose routing. Refer to ST-32-12/81

[bueller]

Got my shims installed and after experimenting with a few different combinations, I've got the Primary Pressure set right at 5.4 bar now. I then tested Dwell from cold and initial readings are fixed at 45. After getting into closed loop, the dwell fluctuates between 36 and 44. If I press the WOT switch at this point, I get a fixed 46-47 or so. I did not adjust the mixture given that these values seem to be more or less where they should be.

I then drove her around for a little while and I can say that it is a massive difference compared to before. The stuttering when accelerating was gone as far as I could notice. Steady power throughout the RPM band!!

However, when I got back to the shop, I checked the dwell again, and the dwell is no longer fluctuating while idling. It shows a fixed 46-47 now just like the WOT was pressed or if I had my O2 sensor disconnected. I'm assuming this shouldn't be happening, but confused on why Dwell reads correctly early on but then acts like it's in open loop. Could this be a bad O2 sensor that works sometimes and doesn't others?

Thanks!

[Bitsyncmaster]

Got my shims installed and after experimenting with a few different combinations, I've got the Primary Pressure set right at 5.4 bar now. I then tested Dwell from cold and initial readings are fixed at 45. After getting into closed loop, the dwell fluctuates between 36 and 44. If I press the WOT switch at this point, I get a fixed 46-47 or so. I did not adjust the mixture given that these values seem to be more or less where they should be.

I then drove her around for a little while and I can say that it is a massive difference compared to before. The stuttering when accelerating was gone as far as I could notice. Steady power throughout the RPM band!!

However, when I got back to the shop, I checked the dwell again, and the dwell is no longer fluctuating while idling. It shows a fixed 46-47 now just like the WOT was pressed or if I had my O2 sensor disconnected. I'm assuming this shouldn't be happening, but confused on why Dwell reads correctly early on but then acts like it's in open loop. Could this be a bad O2 sensor that works sometimes and doesn't others?

Thanks!

It's great your making progress. I would suggest your WOT switch is intermittent. I've seen a few go bad. Just unplug one of the wires off the switch and see if that cures your problem.

[NckT]

I'd have said the same thing what Dave mentioned too re a sticking wide open throttle microswitch.

I'm glad the shims arrived ok and you've noted the difference it makes too.