Rough WARM UP on cold starts backfires in the intake manifold

[zimvsdib]

My car is coming along really well and I'm down to my last issue to resolve. I searched all the threads and didn't find any with these symptoms.

My only issue now is my cold startups. I have those backfires in the intake manifold and the engine sounds fuel starved when revving it.
After it warms up for 2 minutes its fine.


My DWELL is perfect at 40 and i have no vacuum leaks. I checked my vac lines to the WUR again and they are solid. I swapped the WUR with another that was recently rebuild and still had the same issue.

Id appreciate any suggestions on where to look/ test next. BTW its my 100th post!:partyhat:

[Howard1398]

My car is doing the same thing right now too. I even replaced the warmup regulator with no affect as well. Is your frequency valve buzzing?

[zimvsdib]

My car is doing the same thing right now too. I even replaced the warmup regulator with no affect as well. Is your frequency valve buzzing?


Yeah the FV is doing fine. I have one of Hervey's control pressure gauges. I just put that in feeding from the large hollow bolt on the WUR.
I have to wait for the engine to cool down now before i can re-test and take a pressure reading.

I'll take a video when start it tonight.


This car starts and idles great, its only when i give it gas during a "cold warm-up" does it backfire in the intake and sound fuel starved.

[PJ Grady Inc.]

Did you confirm you have vacuum to the regulator when cold or just do a visual check?

[zimvsdib]

Did you confirm you have vacuum to the regulator when cold or just do a visual check?

Hi Robert! thanks for the reply.

I did not preform this test yet.
Rich suggested to connect the vacuum gauge to the WUR on the rear fitting(i guess the fitting facing the front of the car). Would you remove hose to plug in the gauge or install it in-line?
31014
This is the gauge i picked up today.
i appreciate the help as i try to get this car dialed in correctly.


Here is a video of the control pressure gauge reading on a cold start. After it starts it slow climbs to 4 bar as it warms up and stops. I give it a little gas in the video to demonstrate the backfire.


https://www.youtube.com/watch?v=ZLuPItNYiP8&list=UUt3Q9J4zT0xKOOhdNODslmg

[zimvsdib]

I have been monitoring cold start fuel pressure and dwell for the past couple days.
Here is what my dwell looks like after a few minutes of warm up.
Its not as smooth as id like it.


https://www.youtube.com/watch?v=li_hNFkEYKU&index=3&list=UUt3Q9J4zT0xKOOhdNODslmg

[PJ Grady Inc.]

Keep it simple for now! To check the vacuum hookup simply disconnect the vacuum hose going to the base of the regulator and block the engine side of the hose with your finger. If you feel suction at your fingertip then that's not your problem. To check the rest of the circuit let the engine warm up for 5 to 10 minutes (based on your ambient temp) then check for vacuum at the advance can and the thermal vacuum valve should have switched vacuum from the WUR to the advance circuit. Consult the vacuum hose routing decal that should be on the engine cover to help you identify the components and verify hose routing. It's that simple! No need foe gauges yet! Your problem is probably the hose routing unless you have issues with other engine areas.

[zimvsdib]

Keep it simple for now!

Gotcha!

Okay here are my findings.
I get a nice vacuum pulling from the engine to the warm up regulator. Unplugging that hose makes the idle erratic.

Its 90 degrees here so the car warms up pretty quickly. The WUR vacuum tappers off after a bit, then i checked the Advance.
Zero Vacuum on the advance.
The Solenoid is also very hot. The electrical connection is solid but the unit is way hot.
I unplugged the hose from the Thermal control valve on the back of the Solenoid, the Vacuum there is very strong.

I also checked the routing is correct on Thermal control Valve. I can get my hand under the manifold and feel placement on all the hoses is correct.


31020

[PJ Grady Inc.]

Gotcha!

Okay here are my findings.
I get a nice vacuum pulling from the engine to the warm up regulator. Unplugging that hose makes the idle erratic.

Its 90 degrees here so the car warms up pretty quickly. The WUR vacuum tappers off after a bit, then i checked the Advance.
Zero Vacuum on the advance.
The Solenoid is also very hot. The electrical connection is solid but the unit is way hot.
I unplugged the hose from the Thermal control valve on the back of the Solenoid, the Vacuum there is very strong.

I also checked the routing is correct on Thermal control Valve. I can get my hand under the manifold and feel placement on all the hoses is correct.


31020
Are you sure you have vacuum to the solenoid but it;s not allowing vacuum to pass the the advance can when hot and the hose routing is correct? If so it sounds like the solenoid is NG to me! The hot solenoid is another indicator of that too.
oid

[zimvsdib]

Are you sure you have vacuum to the solenoid but it;s not allowing vacuum to pass the the advance can when hot and the hose routing is correct? If so it sounds like the solenoid is NG to me! The hot solenoid is another indicator of that too.
oid

I just replaced my solenoid. The new one sends vacuum to the advance but this one is getting really hot as well. Does that solenoid usually get really warm during operation?

I still have the same cold start backfire in the manifold when i rev the car.

Tomorrow i have some time to try a bunch of things. What should i look at?

Currently vacuum starts at the WUR then switches to the solenoid and advance after warm up.

[DMCMW Dave]

I just replaced my solenoid. The new one sends vacuum to the advance but this one is getting really hot as well. Does that solenoid usually get really warm during operation?


Yes. Keep in mind that that solenoid is energized at idle only. So - when you are going down the road it's "off" and not getting hot. When you have the car sitting idling for a while it is electrically powered all the time and will run warm.

The usual failures are that it just fails (open all the time) or leaks. Neither is particularly common.

[ILM1010]

this sounds like whats happening to my car, starts up fine, then after a couple minutes it quits. after 2 more start ups and going down the road it runs fine. In the beginning when it does quit, in first gear it putts along slow. So after another start up after a few seconds then it kicks in and runs great. When the car is idling, it does shake quite a bit off and on.

[hmcelraft]

Have you check the function and correct install of the Delay valve? See attached.