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View Full Version : Engine Stutter/Dead Spot/Hesitation When Cold



sdg3205
05-25-2011, 09:33 PM
If my car has been sitting for a while (usually a few days), it seems to take a long time for it to accelerate properly.

For the first 5 minutes or so, it will intermittently feel like it isn't firing on all cylinders or its running out of gas. After those five minutes are up it runs like a champ with no hesitations.

At first I thought it could be the fuel filter - I haven't installed my new one yet as I wanted to run a few tanks of gas though it first in case any debris was still around following the fuel tank/fuel pump service.

Or is it just that it's a 30 year old car that demands a decent warm up?

DMCMW Dave
05-25-2011, 09:41 PM
The warmup regulator is either disconnected (check the vacuum lines against the diagram glued to the engine cover) or bad.

sdg3205
05-25-2011, 09:55 PM
Sweet. I can handle that.

Just in case, a new one is $100 after the core is returned?

What breaks in these?

DMCMW Dave
05-25-2011, 10:17 PM
Usually they get plugged up from crap in the gas tank or bad gas.
Failure on a runnning car is kind of unusual IMO. Check the vacuum hoses first. Unfortunately the hose goes under the intake to the 3-port vacuum switch. You can actually reach under there and verify hose routing but it's difficult. More likely one of the vac hoses on the CPR or inline delay valve have simply popped off.

If that all looks OK, take the fuel hoses off and see if the screens on the CPR look plugged.

I think it's more like $165.

Bitsyncmaster
05-26-2011, 05:32 AM
The heater in the WUR may be shot. Without the heater it takes a very long time for engine warm up. Since you run good after warmup your RPM relay must be good (it supplies power to the WUR heater).

I've seen a few (mine for one) heaters burn up the wiring inside the WUR.

sdg3205
05-26-2011, 05:58 AM
The heater in the WUR may be shot. Without the heater it takes a very long time for engine warm up. Since you run good after warmup your RPM relay must be good (it supplies power to the WUR heater).

I've seen a few (mine for one) heaters burn up the wiring inside the WUR.

I know you and I spoke about this only a day or so ago. This was happening before I installed your new SS RPM relay too.

Is there a way to test the heater?

Bitsyncmaster
05-26-2011, 07:29 AM
I know you and I spoke about this only a day or so ago. This was happening before I installed your new SS RPM relay too.

Is there a way to test the heater?

Pull the connector off the WUR. Stick your meter leads into the connector on the WUR (you may need some small wires to get at the pins). You should read around 20 ohms.

David T
05-27-2011, 01:30 PM
The same symptoms can occur with an old/bad set of ignition wires. If they are original or just very old it may be time to change them too but the Control Pressure Regulator is the most likely suspect. Can be verified by checking fuel system pressures as the car warms up. Other cold start-warm-up systems include the spark advance, heat stove, and idle speed-up. To a much lesser degree they will affect cold drivabilty if they are not working right.
David Teitelbaum

DMCMW Dave
05-27-2011, 02:18 PM
If the heater is bad, it just delays the warm-up time (too rich for too long) and emissions issues. It will not impact how it runs very much. Once the thermal vac switch goes to distributor vacuum the WUR enrichment circuit is out of play. The bucking when cold is a lean condition.

sdg3205
05-27-2011, 05:16 PM
The same symptoms can occur with an old/bad set of ignition wires. If they are original or just very old it may be time to change them too but the Control Pressure Regulator is the most likely suspect. Can be verified by checking fuel system pressures as the car warms up. Other cold start-warm-up systems include the spark advance, heat stove, and idle speed-up. To a much lesser degree they will affect cold drivabilty if they are not working right.
David Teitelbaum

All my ignition components are brand new, so yeah it must be the CPR.

I still havent had a chance to trouble shoot it yet as work has been super busy this week.

sdg3205
05-28-2011, 03:21 PM
So I measured the resistance across the WUR and got 18.2 ohms. Not quite the 20 dave spoke of. Acceptable?

With ignition on, i have no voltage on the harness to the WUR, but im not sure if the WUR is powered until the engine starts. Safe to test with engine running?

My vacuum lines look to be okay.

Is it bad for the car to operate without the WUR?

Lastly, if I disconnect the fuel lines to it, how much gas will I encounter? Should I annihilate the rest pressure first by pressing down on the plunger under the air filter?

DMCMW Dave
05-28-2011, 04:13 PM
1 - close enough
2 - should be 12V with the key on. You can disconnect and/or measure it with the engine running, not an issue. This is not your problem anyway.
3 - ok. did you test the function with a vacuum gauge? VAcuum at the CPR cold and at the distributor vacuum switch hot? If the lines are cracked under the intake or the thermal vacuum switch is bad, you can't tell from a visual.
4 - You can't run the car with the fuel lines disconnected, so yeah, it's bad to run the car without a CPR. If you mean after it warms up and it's running OK, then it's OK. I have seen a CPR fail where the engine was set very lean, that's not good.
5 - Not much. Have rags handy and don't do it on a hot engine. I'm not big on relieving pressure by pressing the flap as it floods the engine.



So I measured the resistance across the WUR and got 18.2 ohms. Not quite the 20 dave spoke of. Acceptable?

With ignition on, i have no voltage on the harness to the WUR, but im not sure if the WUR is powered until the engine starts. Safe to test with engine running?

My vacuum lines look to be okay.

Is it bad for the car to operate without the WUR?

Lastly, if I disconnect the fuel lines to it, how much gas will I encounter? Should I annihilate the rest pressure first by pressing down on the plunger under the air filter?

Bitsyncmaster
05-28-2011, 04:14 PM
So I measured the resistance across the WUR and got 18.2 ohms. Not quite the 20 dave spoke of. Acceptable?

With ignition on, i have no voltage on the harness to the WUR, but im not sure if the WUR is powered until the engine starts. Safe to test with engine running?

My vacuum lines look to be okay.

Is it bad for the car to operate without the WUR?

Lastly, if I disconnect the fuel lines to it, how much gas will I encounter? Should I annihilate the rest pressure first by pressing down on the plunger under the air filter?

Your 18 ohms is good. You will only get voltage with the engine running. Do not purge rest pressure by pushing the air plate as that shoots gas into the intake. You can power the lambda with a jumper to the RPM connector to remove rest pressure or you can back off the nut where the primary pressure regulator is. Or just wait overnight. I'm not sure show much gas will come out the WUR hoses with full rest pressure. It may not be as much as removing a pump line.

sdg3205
05-28-2011, 05:04 PM
Dave S and Dave M,

Im a little confused - so is there voltage with the key on II or only when the engine is on? As i read it I think you're both saying something different.

Dave S. - No, I dont have a vacuum tester. If I can't resolve it on my own I'm making a trip to DMCNW next week anyway to see Toby and pick up some parts.

I'll get back to you!

Cheers and thanks so much for all the help.

Bitsyncmaster
05-28-2011, 09:08 PM
Dave S and Dave M,

Im a little confused - so is there voltage with the key on II or only when the engine is on? As i read it I think you're both saying something different.



The same relay that drives the fuel pump drives the WUR/lambda. So it should only be 12 volts with the engine running.

sweetp01569
07-21-2013, 12:05 AM
The same relay that drives the fuel pump drives the WUR/lambda. So it should only be 12 volts with the engine running.

I hope it's OK to reply to an older post but could you clarify Dave about the availability of voltage to the CPR? You said the engine needs to be running to have voltage at the CPR? I don't have voltage there with just the key turned but per the fuel pressure testing procedure in the probst book it sounds like I should just run fuel pump with jumper with engine not running and check cold and warm control pressure which checks the ability of the CPR to increase pressure when energized. I am confused. I'm not sure if I have electrical opens on the CPR circuit or not. No voltage at the blue bulkhead connector for CPR circuit with just key turned.

Thanks,

Paul
Vin 10944

Bitsyncmaster
07-21-2013, 03:10 AM
I hope it's OK to reply to an older post but could you clarify Dave about the availability of voltage to the CPR? You said the engine needs to be running to have voltage at the CPR? I don't have voltage there with just the key turned but per the fuel pressure testing procedure in the probst book it sounds like I should just run fuel pump with jumper with engine not running and check cold and warm control pressure which checks the ability of the CPR to increase pressure when energized. I am confused. I'm not sure if I have electrical opens on the CPR circuit or not. No voltage at the blue bulkhead connector for CPR circuit with just key turned.

Thanks,

Paul
Vin 10944

No you will not get voltage to the CPR with a simple jumper powering the fuel pump via the RPM relay. You would need a jumper with three pins so you could also power the CPR pin. Or just test it with the RPM relay installed and engine running.