Temporary lack of power after first, cold startup

[jawn101]

I have to emphasize that this is *not* another cold-start thread. I have no problem cold, warm or hot starting at all. The engine runs and starts great under all circumstances except the following.

When I first start up in the morning after the car's sat overnight, there is a distinct lack of power until everything is fully warmed up. I drive maybe 1500 feet from my driveway to the stop sign at the entrance to my neighborhood. Mostly coasting. Then when I go to turn onto the main road, the lack of power is so dramatic that I've almost been t-boned trying to exit before. Then by the time I get to the next stop sign on the main road (2000 feet maybe) the issue is gone and the engine has full power until tomorrow morning.

During the "low power" phase, the engine sounds/feels like it's stumbling and could be starved for fuel. I've confirmed that my vacuum system is tight as can be with all silicone hoses, the fuel system has plenty of rest pressure and the idle is smooth and even after warmup. It does hunt somewhat while the lambda is heating up but after that there's not a hint of hunt. FV is buzzing and working if that matters. Tested the duty cycle on it yesterday and it seems a little high, but that could be my meter. Fuel pump looks and sounds to be in good condition and the tank is nice and clean. All the fuel lines in the engine are brand new stainless. Pickup and pump->hard line hoses are older.

Any thoughts on what to check out? I had a suggestion it could be the WUR, is there any way to test that without having another one on hand?

[David T]

Sounds like a problem with the CPR, aka warm-up regulator. It can be verified by watching the control pressure as the motor warms up.
David Teitelbaum

[jawn101]

Sounds like a problem with the CPR, aka warm-up regulator. It can be verified by watching the control pressure as the motor warms up.
David Teitelbaum

I know I sometimes make it sound like I know what I'm talking about, but I have no idea how to do that :)

[Bitsyncmaster]

You need to have the mixture adjusted properly (engine hot) to have a good WUR adjust the cold mixture properly. So if you have checked the hot mixture, then it would be a problem with the WUR. One thing to check, is the screen on the WUR inlet hose.

[jawn101]

You need to have the mixture adjusted properly (engine hot) to have a good WUR adjust the cold mixture properly. So if you have checked the hot mixture, then it would be a problem with the WUR. One thing to check, is the screen on the WUR inlet hose.

I had no idea there was a screen. Where is that located, under one of the banjo bolts? I see that Houston sells "rebuilt" CPRs with a core charge, so that means they must be repairable - anyone know what's involved with that?

I believe the mixture to be pretty fair. I will check that again today but I am not 100% convinced of my meter's accuracy as what should be a fixed reading on the FV with the RPM relay jumpered doesn't read precisely what it should.

[DMCMW Dave]

If this came on suddenly, before you start throwing parts at it just make sure all the vacuum hoses on the engine are connected correctly per the diagram on the engine cover. If either of the hoses falls off the warmup reguator, or gets disconnected along the way, it will act exactly as you are describing.

[jawn101]

If this came on suddenly, before you start throwing parts at it just make sure all the vacuum hoses on the engine are connected correctly per the diagram on the engine cover. If either of the hoses falls off the warmup reguator, or gets disconnected along the way, it will act exactly as you are describing.

It did seem to start rather suddenly, but long after I replaced all the vacuum hoses. So the routing is correct, but that doesn't mean something isn't loose. I do believe the vacuum system to be very tight as taking my CO adjustment plug out causes a very dramatic change in the engine's behavior, and that's a pretty small leak. I did check the hose from the delay valve to the front of the WUR, but I will go check the rest of that area now and see if there's anything interesting.

[Bitsyncmaster]

I had no idea there was a screen. Where is that located, under one of the banjo bolts? I see that Houston sells "rebuilt" CPRs with a core charge, so that means they must be repairable - anyone know what's involved with that?

I believe the mixture to be pretty fair. I will check that again today but I am not 100% convinced of my meter's accuracy as what should be a fixed reading on the FV with the RPM relay jumpered doesn't read precisely what it should.

Yes the screen is under the banjo bolt. Best way I've found to clean it is with compressed air. You can use those air cans if you don't have a compressor.

[jawn101]

Let it be known that Dave Swingle is some kind of shaman. After pulling the WUR off and inspecting the vacuum lines, it seems that the delay valve had fallen behind the regulator, bending the line at the front edge at a strange angle and causing the tapping to puncture it. I pulled the hose off, trimmed the half-inch that was punctured and re-attached it. The hesitation cold is completely gone now. I am going to go find a way to tie up that delay valve so this doesn't happen again.

Thanks to all three Daves! :)

[DMC5180]

As long as your at it check the Blue Bulkhead connector. I discovered this on my car when it had the same condition as yours a few years ago. The pin that is pushed back is the power for the WUR heater. It was a bit of pain to get at the back side so I could reset the terminal lock tabs. Btw: the stumbling condition was most prevalent on cool mornings temps in 40's-50's if I didn't let the car warm up a few minutes.

8910

[jawn101]

As long as your at it check the Blue Bulkhead connector. I discovered this on my car when it had the same condition as yours a few years ago. The pin that is pushed back is the power for the WUR heater. It was a bit of pain to get at the back side so I could reset the terminal lock tabs. Btw: the stumbling condition was most prevalent on cool mornings temps in 40's-50's if I didn't let the car warm up a few minutes.

8910

Great tip Dennis. I just inspected those connectors while I had the interior carpets out for my dynmat install, and the pins are all in fine condition. But it's great info for anyone who might find this thread later.

[DMC5180]

If you were messing with any of that stuff, I would confirm you are getting power at the grey plug on WUR. (Pin 1) Make sure the other wire has continuity to ground (pin 2).

Eh Nevermind, I didn't see you had found the problem in Post #9

[DMCMW Dave]

As long as your at it check the Blue Bulkhead connector. I discovered this on my car when it had the same condition as yours a few years ago. The pin that is pushed back is the power for the WUR heater. It was a bit of pain to get at the back side so I could reset the terminal lock tabs. Btw: the stumbling condition was most prevalent on cool mornings temps in 40's-50's if I didn't let the car warm up a few minutes.


That's really a good one to know. I don't often run cars around here when it's cold (we store all cars indoors, and rarely take them out in the winter, and even more rarely fire one up at an ambient much below 65F), and I have wondered what happens if that heater isn't there since for the most part engine heat will get the regulator stabilized pretty quickly. I think in the summer you'd never miss it.

It would be a strange and short-lived symptom as lacking the heater would actually cause a rich condition for a short time soon after startup. Lacking the vacuum connection causes a lean stumble on acceleration when cold (which is where this thread started).

[jawn101]

That's really a good one to know. I don't often run cars around here when it's cold (we store all cars indoors, and rarely take them out in the winter, and even more rarely fire one up at an ambient much below 65F), and I have wondered what happens if that heater isn't there since for the most part engine heat will get the regulator stabilized pretty quickly. I think in the summer you'd never miss it.

It would be a strange and short-lived symptom as lacking the heater would actually cause a rich condition for a short time soon after startup. Lacking the vacuum connection causes a lean stumble on acceleration when cold (which is where this thread started).

Checked and my heater power is good, which I figured since the symptoms completely vanished after repairing that hose. I'm still amazed that Dave S nailed that one so quickly and based on my crap description :)