Stuttering under acceleration when warm

[bueller]

Got my pressure tester and I'm getting right at 4.9 bar for Primary Pressure. This is certainly at the bottom of the 'Checking Value' per the manual so I'll be adding some shims once they arrive to get it to the 5.4 recommended number for the UK Performance exhuast (though mine is a DPI Spec 1).

Control Pressure was right at 30 psi or 2.1 bar when started cold (first thing in the morning) with vacuum and electrical disconnected from the WUR at approximately 80 degrees F outside temp so that looks to be pretty close to the range of the chart in the book. Control pressure slowly increased but didn't seem to want to go above about 42 PSI or 2.9 bar even after idling for 10-15 minutes. Rest pressure stayed above the 1.7 minimum (2.1 bar after 10 minute wait) so that looks reasonably solid.

Does the 42 PSI control pressure after 10+ minutes indicate any issues with the WUR? I understand that it is really just used during warmup and I don't really have any noticeable issues with a cold start or initial idle, but the lower number makes me a bit curious.

Thanks!

[Bitsyncmaster]

Did you have the vacuum and electrical heater back on the WUR when testing warmed up? I normally get about 50 PSI.

[bueller]

Did you have the vacuum and electrical heater back on the WUR when testing warmed up? I normally get about 50 PSI.

Yes, I did try attaching the Vacuum and Electrical back to the unit towards the end of my testing and it didn't seem to make much of a difference. I did notice that the electrical connections were a bit corroded so I'm not sure if that was possibly related. I've cleaned the contacts with some special cleaner that is electronics safe, but I haven't tested since then as I wanted to let the car cool back down.

[Bitsyncmaster]

Yes, I did try attaching the Vacuum and Electrical back to the unit towards the end of my testing and it didn't seem to make much of a difference. I did notice that the electrical connections were a bit corroded so I'm not sure if that was possibly related. I've cleaned the contacts with some special cleaner that is electronics safe, but I haven't tested since then as I wanted to let the car cool back down.

It should have voltage with the engine running. If the heater is not working the engine has poor cold running performance for a longer time. The voltage comes from the RPM relay.

[bueller]

It should have voltage with the engine running. If the heater is not working the engine has poor cold running performance for a longer time. The voltage comes from the RPM relay.

I'll check for voltage next time I'm in the shop. Should it be a standard 12v-ish that I'm seeing there? I run your RPM relay so I'm sure that part is all fine, but will verify no wiring issues.

[Bitsyncmaster]

I'll check for voltage next time I'm in the shop. Should it be a standard 12v-ish that I'm seeing there? I run your RPM relay so I'm sure that part is all fine, but will verify no wiring issues.

Yes one pin should have the normal 12+ volts with the engine running and the other pin is ground.

[bueller]

I just ran out to check things and the voltage on the electrical plug when running was right where it should be. Granted, I didn't get to see a full cold to warm cycle as I didn't let it sit overnight, but when I plugged the electrical back in while it was running, I'm getting a solid 50 PSI control pressure now when warm. My guess is that corrosion noted earlier on the electrical connection may have caused an issue with my previous tests.

I'll check again in the morning from cold to make sure the pressures are where they should be but if that checks out, then I'll continue to wait for my shims to bring up the Primary Pressure and then I'll set the dwell appropriately and see what happens.

Thank you all for the continued assistance!!

[NckT]

50 psi == 3.45 Bar so this is good warm control pressure.

Have you done the test to check the vac delay valve?
On warm engine with control pressure at 50psi (I keep having to convert from Bar) disconnect the vacuum pipe that comes from under the inlet manifold that goes to the T plastic piece at the control pressure vacuum piping.
Apply a vacuum to this part.
As soon as the vacuum is released, the control pressure should go down to between 1.2 and 1.8 Bar (17-26 psi) and stay there for approx 8 to 12 seconds, then return back to 3.4 bar (50 psi).

Keep up the good work, it's nice to see some diagnostics going on instead of part swapping

[bueller]

Have you done the test to check the vac delay valve?
On warm engine with control pressure at 50psi (I keep having to convert from Bar) disconnect the vacuum pipe that comes from under the inlet manifold that goes to the T plastic piece at the control pressure vacuum piping.
Apply a vacuum to this part.
As soon as the vacuum is released, the control pressure should go down to between 1.2 and 1.8 Bar (17-26 psi) and stay there for approx 8 to 12 seconds, then return back to 3.4 bar (50 psi).

Keep up the good work, it's nice to see some diagnostics going on instead of part swapping

I haven't done a vac delay valve test yet. Based on some reading I've done the last couple of days, it appears I would need a vacuum pump to test this which I don't currently have. Would something like the Mityvac MV8000 (http://www.mityvac.com/pages/products_hvpk.asp) be appropriate or can this test be done with something less precise like a shop vac or something else that can suck?

I am a big fan of understanding the inner-workings of things I own. The K-Jet is definitely more complex than I'm used to so I've done a lot of reading of manuals and online here. My knowledge has gotten better but I'm a far cry from where I'd like to be. Thanks again to you and the many others who help newbies like me!

[Bitsyncmaster]

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).