Will excessive cranking cause premature leaning by the WUR?

[DMC1890]

While troubleshooting my cold-start rough idle issue, I decided to test the WUR by disconnecting the electrical connector to the WUR. I then managed a start, then quickly went back to reconnect the WUR while monitoring the pressure.

With cold engine, and 72F ambient, my initial control pressure was 2.45 bar. After 30 seconds, I had 3.65 bar, with some continuing slow rising after that. No problem there that I can tell.

But then I wonder - if I had to crank excessively before achieving start-up, wouldn't the WUR have already leaned out the mixture?

I've seen similar issues with carburetor-ed engines with electrically-heated chokes - prolonged starting/cranking resets the choke before actual start-up.

[Ron]

It might make the idle off very briefly, but I doubt it would affect starting much.
Assuming your engine was Dead Cold, I.E., engine radiant temperature was equal to the Ambient Temperature, it sounds like your WUR/CPR is within specs. It is part of the Warm Up Circuit, so assuming the CO is within specs also when it warms up, I believe its effect on starting would be insignificant. I would suspect the Thermal Time Switch-Cold Start Valve operation since they make up the Starting Circuit. (It looks at the engine temperature independent of the WUR/CPR....)

Comparing to a carbed system- After excessive cranking, the operator should realize the choke is open too much and compensate by pumping the pedal several times to inject more fuel. A D's TTS would automatically do the same thing.

How does it act with a shot of starting fluid?
Vacuum leak??

[DMC1890]

Actually, I can almost always count on a good burst of immediate start-up firing, thanks I presume to a working cold-start injection system. What occurs next seems to be the main issue. If it idles roughly and dies, a subsequent start-up will indeed give another immediate burst of rpm. But by now I'm thinking I've used up half of the WUR's 'cold virginity'. And it then can get only worse on further restart attempts.

If I run it every 2-3 days, it behaves well. But if it sits for 2-3 weeks, I see this problem. I think I may exacerbate the situation if I cycle the ignition switch 2-3 times prior to cranking - thinking that this will prime the fuel pump, but while I'm also heating up the WUR.

I know it sounds tacky, but I wish I had a separate switch to prime the fuel pump, and another switch to enable the WUR circuit after the engine has attained idle.

Robert

[David T]

A cold engine does initially start up on the fuel from the CSV. Depending on the calibration of the WUR and the condition of the engine tune (how worn the spark plugs are etc) next determines the quality of the idle till the engine warms up. Excessive cranking can allow the WUR to get heated up by the heater element inside reducing the amount of extra fuel the motor needs because it is still cold because it hasn't started yet. All of these systems have to work together in a coordinated manner but they are not "smart" or interconnected except by the motor itself. Hard to compare directly to a carbureated motor with a choke, they have different but similar characteristics. Excessive cranking is no good for a lot of reasons. Don't forget there are other systems that are operating during warm-up that also can affect the idle like the vacuum advance. They ALL need to work and work correctly to produce a good quality idle during warmup. As I said earlier, if the motor needs a tune-up or if you have a bunch of leaking vacuum hoses the idle can also be bad.

[Ron]

Actually, I can almost always count on a good burst of immediate start-up firing, thanks I presume to a working cold-start injection system. What occurs next seems to be the main issue. If it idles roughly and dies, a subsequent start-up will indeed give another immediate burst of rpm. But by now I'm thinking I've used up half of the WUR's 'cold virginity'. And it then can get only worse on further restart attempts.

If I run it every 2-3 days, it behaves well. But if it sits for 2-3 weeks, I see this problem. I think I may exacerbate the situation if I cycle the ignition switch 2-3 times prior to cranking - thinking that this will prime the fuel pump, but while I'm also heating up the WUR.

I know it sounds tacky, but I wish I had a separate switch to prime the fuel pump, and another switch to enable the WUR circuit after the engine has attained idle.

Robert
Sorry, I thought you meant it had a problem starting, then ran rough for a short while.
Thoughts:
Your control pressure is on the upper edge of spec [~2.1-2.4 BAR @ 72 F Engine Radiant (Not Ambient) Temp], so if your primary pressure is on the low side, I can see it running rough for a short time.

We usually think of a "warm" engine being ~180-190°F, but the WUR/CPR stops adjusting at 104°F (40°C). The engine and the 2 heating elements in the WUR/CPR will bring it up very fast. (E.G., If you adjust the WUR/CPR, you only get one chance to check its pressures -- then you have to let it cool off over night.) A laser thermometer is your friend...

When you cycle the ignition switch to prime the fuel pump, it doesn't cause the WUR/CPR to heat up. The RPM Relay sends power to the WUR/CPR when the engine is rotating only!

If I was 100% sure it was lean during a true cold start, I'd nudge the CO a tiny bit rich and see how it acts...just for a test.

[Bitsyncmaster]

When you cycle the ignition switch to prime the fuel pump, it doesn't cause the WUR/CPR to heat up. The RPM Relay sends power to the WUR/CPR when the engine is rotating only!

That is true with my solid state RPM relay. My prime does not turn the second output on. The OEM relays do turn on both outputs if they prime.

I agree it sounds like it could be your base mixture adjustment. Setting the mixture to book values seems to be the best for engine starting also.

[DMC1890]

I started it up yesterday, after a 2-day rest, and it started and idled instantly. I did not give it extra 'priming' cycles.

It's not clear what the differences are between a 2-day rest, and a 4-week rest.

Dave M, may I ask how you avoid energizing the WUR on the initial pump prime? Do you look for a 'real' tach signal for the WUR output rather than just a single blip (which I presume is sufficient for the pump output)? If so, do you differentiate between cranking RPM and idle RPM?

Robert

[Ron]

That is true with my solid state RPM relay. My prime does not turn the second output on. The OEM relays do turn on both outputs if they prime.

I agree it sounds like it could be your base mixture adjustment. Setting the mixture to book values seems to be the best for engine starting also.

I stand corrected!...but only for a second (pun intended) -- I'm assuming you said, "if they prime", because the Ignition Control Unit could fire the Coil when it is first powered up, which an OEM Relay can falsely interpret as "the engine is rotating" and lie to the RPM Relay "for about one second" (contrary to the manuals description, and, in line with what Robert asked ;-)?

[Ron]

I started it up yesterday, after a 2-day rest, and it started and idled instantly. I did not give it extra 'priming' cycles.

It's not clear what the differences are between a 2-day rest, and a 4-week rest.

Next time it sits for weeks, you might pretend it has a carb and manually hold the choke shut to see if it runs ok for a bit then starts running rich...AKA unplug the WUR/CPR?:)

[Bitsyncmaster]

When my RPM relay gets power (from the key on) I do the pump prime (run the pump for 1.5 seconds). I then wait with software looking for an ignition pulse to turn the pump and second outputs on. I keep both outputs on until there is no ignition pulse for one second.

When I was designing my RPM relay I debated if I should have two switched outputs or just one since it takes about $5 more in parts to have have two. Since I'm not space limited with the RPM relay I decided to keep two outputs even though there is really not much gained with two.

Some of the OEM RPM relays use two contacts on the relay to make the two outputs switched even though both switch at the same time. Those units tend to have problems with some of them not switching that second output on because both contacts don't always work. The later OEM RPM relays just use one relay contact and the circuit board connects both outputs. The failure of the OEM units is 99% caused by broken solder joints on the relay to circuit board soldering. The reason the solder joints break is the circuit board is single sided and the heating and vibration put stress on the solder joints.

[DMC1890]

Thanks Ron and Dave M.

I concur that initially unplugging the WUR will help with the startup after hibernation, and in fact have observed it. But, if I take a gamble and don't do that, does anyone know of a way to get the control pressure down temporarily after the WUR has heated up prematurely - perhaps with the vacuum inputs to the WUR?

[David T]

The least invasive thing to do is just wait a few minutes. It should cool off rapidly. The WUR senses temperature 2 ways. One is from the internal heating element and the other is from the valve cover. If the motor hasn't started the valve cover will be cold and cool the WUR quick. The vacuum portion of the WUR is only for sending a pulse of fuel like an accelerator pump in a carburetor would do and only once the motor warms up.

[DMC1890]

I suppose you're right. What I was thinking was to do step 3.c, on page D:02:01 (apply vacuum directly to WUR lower chamber) to force the lower control pressure for starting. But by the time I go find my vacuum pump and hook it up, the WUR heating element may have cooled off. BTW, doesn't the vacuum enrichment normally work only on a cold engine?

Robert

[Ron]

I suppose you're right. What I was thinking was to do step 3.c, on page D:02:01 (apply vacuum directly to WUR lower chamber) to force the lower control pressure for starting. But by the time I go find my vacuum pump and hook it up, the WUR heating element may have cooled off. BTW, doesn't the vacuum enrichment normally work only on a cold engine?

Robert
I think you meant 3.b?

You might try, disconnecting and plugging the vacuum line that does not have the delay valve. Since it usually starts (but then dies), it might create enough vacuum in the lower chamber before it dies to deflect the diaphragm down making it richer. (The delay valve holds for ~10 seconds.) No idea how much it would change the A/F ratio...might flood the heck out of it, especially after it stared idling a while...Plugging the port too might help if it's too rich.

Thoughts:
I agree it should cool off rapidly as David T said, IFF it does not start/run. Mainly because I don't think short cranking times does much, considering the OEM purpose/design. 104°F is not very hot, and that is the top end of its effectiveness. All that and the pressure you reported indicates the WUR/CPR is on the high side but ok (at least at that radiant temp), which makes me think the problem is elsewhere, even if related to the WUR/CPR....
FWIW, I would double check all of the things I'm sure you already looked at (timing, vacuum routing/leaks, TTS & CSV operation, ..., set CO last). Then confirm that the primary pressure is correct and not throwing off the ratio with the control pressure, and then record the radiant temps-control pressures as it warms up.
If it turns out that the control pressures are off, you can adjust the WUR/CPR.

(Sorry for the repetitions ;-)

[DMC1890]

Thanks to all you guys.

At this point, it is a moot issue for me. With the current weather here in Houston, I'll probably drive the D every 2-3 days. And in that mode, it starts and runs perfectly!

But I think I've learned a good bit now about the WUR as well as the RPM relay, which will come in handy in the future.

[David T]

If the motor does not start right up (even cold) or idle badly when cold, maybe it is time for a tune-up? Worn spark plugs, bad wires, dirty fuel injectors, vacuum leaks can all contribute to hard starting and excessive cranking. Even with a perfectly operating WUR, the A/F ratio is not optimum and the motor will not run all that great til it warms up. These systems are to get the motor started quickly and run as smooth as possible till it can warm up and get into closed loop.