# Lousy cold start on CIS-Basic



## Longitudinal (Nov 13, 2004)

I picked up a 1979 Audi Fox, and have been steadily working on making it run. It starts horribly when cold, and requires several starts before it will idle, then several minutes before it is drivable. 
I am thinking this is a cold start control pressure problem, caused either by no power to the CPR or a bad CPR (less likely.) Sound reasonable? I have not yet checked for power to the CPR. Should it have power whenever the key is on?


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## Longitudinal (Nov 13, 2004)

*Re: Lousy cold start on CIS-Basic (Longitudinal)*

I know that somebody who has viewed this thread has advice to offer. I have answered far more CIS-related questions than I have asked, folks.


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## WackyWabbitRacer (Apr 24, 2001)

*Re: Lousy cold start on CIS-Basic (Longitudinal)*


_Quote, originally posted by *Longitudinal* »_I am thinking this is a cold start control pressure problem, caused either by no power to the CPR or a bad CPR (less likely.) Sound reasonable? 

A Control Pressure problem will cause a cold start situation. Also a faulty Cold Start Injector can cause the same situation.
In most cases, a Control Pressure Regulator (CPR) over time will have a buildup of gas shellac inside it. Consequently the control pressure will be higher than the normal specification of about 24 psi for a cold start.
So if the cold control pressure is too high, the fuel mixture is not rich enough during the initial cold start period of time.
A CPR is nothing more than a hydraulic choke. On a cold start, the control pressure is low for a richer fuel mixture; once the engine reaches normal operating temperature, the control pressure increases to about 58 psi for fuel economy and lower emissions.
Cheers, WWR.


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## Longitudinal (Nov 13, 2004)

*Re: Lousy cold start on CIS-Basic (WackyWabbitRacer)*


_Quote, originally posted by *WackyWabbitRacer* »_A Control Pressure problem will cause a cold start situation. Also a faulty Cold Start Injector can cause the same situation.

I should have mentioned that it fires flawlwessly on the cold start injector, but dies once it has burned off the fuel from the CSV. It will start again on fuel from the CSV, then immediately die, again and again, depending on how cold the engine is. If it is in the heated shop, it dies two or three times and will then idle. If it's outside in the Ohio winter, it will take six or eight starts until it will idle, and a minute or two of idling before it will move on its own power, and then not well at all until it has warmed up.


_Quote »_So if the cold control pressure is too high, the fuel mixture is not rich enough during the initial cold start period of time.
A CPR is nothing more than a hydraulic choke. On a cold start, the control pressure is low for a richer fuel mixture; once the engine reaches normal operating temperature, the control pressure increases to about 58 psi for fuel economy and lower emissions.
Cheers, WWR.

Exactly! This is why the CPR is my suspect. If I want to test control pressure, can I test it at either end of the "in" hose for the CPR?


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## WackyWabbitRacer (Apr 24, 2001)

*Re: Lousy cold start on CIS-Basic (Longitudinal)*


_Quote, originally posted by *Longitudinal* »_ If I want to test control pressure, can I test it at either end of the "in" hose for the CPR? 

The best method to measure the control pressure and system pressure is to use a CIS Pressure Tester.
You want to test the control pressure as it comes back into the top of the fuel distributor from the CPR. This is where the control pressure applies a counterforce to the top of the control plunger.
The amount of this counterforce (ie psi) determines how high the control plunger moves upward. Lower the control pressure, higher the movement of the plunger; higher the control pressure; less upward movement of the plunger. 
Cheers, WWR.


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## Longitudinal (Nov 13, 2004)

*Re: Lousy cold start on CIS-Basic (WackyWabbitRacer)*


_Quote, originally posted by *WackyWabbitRacer* »_
The best method to measure the control pressure and system pressure is to use a CIS Pressure Tester.

I have a Mac master fuel injection testing kit with all the CIS fittings.

_Quote »_You want to test the control pressure as it comes back into the top of the fuel distributor from the CPR. This is where the control pressure applies a counterforce to the top of the control plunger.

Hmm. Then I misunderstood the direction of flow. I had thought that the CPR bled fuel pressure off from above the plunger, and what it bled off went through the CPR and returned to the tank by way of going through the other hose on the CPR, into the FD and then back to the tank from there. 

_Quote »_The amount of this counterforce (ie psi) determines how high the control plunger moves upward. Lower the control pressure, higher the movement of the plunger; higher the control pressure; less upward movement of the plunger.

COrrect, for any given air flow.


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## tolusina (Oct 19, 2004)

*Re: Lousy cold start on CIS-Basic (Longitudinal)*

It's an old car, a very old car.
Get down to the basics,
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Start with a valve adjustment, no ifs, ands or buts, just do it.
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Next, the ignition distributor. 
Set dwell to 45° (50% duty cycle). Check to see if dwell varies when vacuum is applied to the vacuum advance unit, if it does, the breaker plate is worn out, replace it.

Check to see if dwell changes more than ±1° with engine RPM, if it does, the distributor shaft bushings are shot, replace them or the complete distributor. Worn shaft bushings were very common on pre 1.8 liquid cooled VW 4s due to poor machining tolerances between the oil pump drive bore and the distributor shaft bore causing side loads on the distributor shaft bore. Any specific engine that wears distributor shaft bushings will wear those bushings to one side only, replacement distributors will wear in exactly the same place.

Twist the rotor clockwise from the top, it should rotate 10° or so, spring back to rest when released. That's your base centrifugal advance test.

Apply and hold vacuum to both chambers of the vacuum advance chamber (one at a time), both should hold vacuum, both should cause the breaker plate to rotate several degrees, the breaker plate should return to rest when vacuum is released.

Do NOT think of the flat side of the vacuum advance as 'retard', think of it as instant advance because that's exactly what it does as soon as the throttle is opened and vacuum is removed.
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_Quote, originally posted by *Longitudinal* »_
I have a Mac master fuel injection testing kit with all the CIS fittings...... 

If that gauge set has no shut off valve towards the control pressure regulator, it's almost useless for CIS testing. 
To overcome that deficiency, use hose pinch pliers to close the line to the CPR as required, more comments on this below.


_Quote, originally posted by *Longitudinal* »_...Hmm. Then I misunderstood the direction of flow. I had thought that the CPR bled fuel pressure off from above the plunger, and what it bled off went through the CPR and returned to the tank by way of going through the other hose on the CPR, into the FD and then back to the tank from there. ..... 

I think you had it right. Closing the test gauge line to the CPR proves you are correct.
Closing the line to the CPR and the bleed/return path forces full system pressure to the top of the control piston causing a very lean mixture, lean enough that you should expect and anticipate a CIS engine to lean stall/quit at idle while testing system pressure, best to test system pressure off idle.
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OK, valves are now adjusted, ignition is all good, system pressure is on, residual pressure is good, cold and hot control pressures are good. RIGHT?
Engine fully warmed, adjust mixture at idle just like a carbureted engine, though the screw turns in reverse.
As you turn the mixture screw in and out, you'll find a range where it runs pretty OK, outside that range it's too rich or lean.
Get to that sweet spot, turn the mix screw counter clockwise until idle just starts to drop off, find the drop by ear or with a tach, I've found an experienced ear more effective than a tach, but an inexperienced ear is useless.
You've found the lean drop point of the mixture range, that's just about the perfect setting to pass smog, not quite perfect for a car that's actually to be driven. 
Get back off the lean drop point and into the edge of the sweet range, add about 1/32 of a turn clockwise and call it done.







_Modified by tolusina at 12:45 PM 1-10-2009_


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## tolusina (Oct 19, 2004)

*Re: Lousy cold start on CIS-Basic (Longitudinal)*


_Quote, originally posted by *Longitudinal* »_....... I have not yet checked for power to the CPR. Should it have power whenever the key is on?


The CPR should be powered whenever the fuel pump(s) run, same for the Auxiliary Air Regulator.


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## Longitudinal (Nov 13, 2004)

*Re: Lousy cold start on CIS-Basic (tolusina)*

Converted to Bosch electronic ignition, so distributor is the late style mechanical/vacuum advance. Timing is spot-on. 
Hydraulic lifter 1.8L engine. 
Gauge has shut-off valve, and without it is quite useful for CIS testing. You can test system pressure and pressure at the injectors. That's pretty far from useless.


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## Longitudinal (Nov 13, 2004)

*Re: Lousy cold start on CIS-Basic (Longitudinal)*

OK, I got it running pretty well. Turns out it had a low voltage condition at the fuel pump. Voltage would read as low as 8.9V! The problem seemed to be on the power supply side; I wired up a whole new circuit from the battery through a relay to the pump and the car runs SUBSTANTIALLY better now. It still stutters a bit when accelerating on a cold engine, but it runs fine once warmed up. 
Surprisingly, pressure supplied to the FD was on the low side of spec until voltage dropped to 8.9V, at which pressure dipped to 45lbs, clearly not enough to do any more than idle roughly.
Due to a problem with a partially collapsed banjo fitting due to a PO's over-tightening, I had not checked supply pressure until recently. Apparently, I had crossed it off the mental list without actually doing the test.


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