The Sound of Solenoids

[ftm1776]

My car: 1991 MK2 1.6 diesel, NA

The injection pump was recently rebuilt by a reputable diesel specialty shop in Portland, OR…..Diesel Fuel Injection Service. I has the two solenoids; fuel shutoff and cold start.

They look the same, but have different Bosch part numbers.

The fuel shut valve will make an obvious “click” when energized with a 12 volt lead.
The cold start valve makes no such sound. Thinking the wire to it might be temperature controlled, I jumped directly from the battery…….still no click.

I tried to remove the cold start valve using a large crescent wrench, but it felt too tight and I didn’t want to break anything. The aluminum housing doesn’t look to strong. I put some WD-40 on and left it till tomorrow.

One of the techs at DFIS told me that some of the Bosch solenoids cannot be heard very easily.

Should the cold start solenoid make an audible click when energized with 12 volts directly from the battery???
If not, can I take that as a sign to replace it??

[TylerDurden]

Not sure you have a cold-start solenoid... is there a lever in the cabin?

There sometimes are other solenoids by the timing plunger... ALFB (interruptible load sensitive start of delivery ) being one.

If you have a pic, it will help.

[thomas m]

Picture of what I call the "cold start solenoid"........some pumps don't have it.



It's in there pretty tight and that housing is dainty....I suppose I could grap the aluminum housing with a padded pair of channel lock pliers and put a little more twist to it??

I just want to know if I should be able to hear it activate. If yes, I might have to replace it.

Yes, there is a cold start pull handle to the left of the steering wheel.

[TylerDurden]

You probably won't hear that one. That's an ALFB.


"The ALFB can be deactivated to reduce HC emissions generated by the diesel engine when it is cold (< 60'c). This process employs a solenoid valve ( to block the fuel. This solenoid valve is open when de-energized."

ALFB will retard timing unless the solenoid has power.

[ftm1776]

How do I know that it is functioning correctly?? (I can't find it on my Bentley wiring diagram.)

Or at least that it is getting power when it is suppose to get power??

I can't tell that the solenoid is activating unless I remove it and look....maybe not even then.

Bottom line is that if it doesn't affect engine start, idling or anything else I'd just as soon not have it on the pump,
but will have to live with it, I guess.

PS: I think I see. When the engine is running at less than 60C or 140F, the ALFB would be de-activated by 12 volts to the solenoid until the engine warms up. So, I should see 12 volts at the solenoid, just after start-up, with the engine cold, i.e., less than 140F. Once above 140F, there should be no voltage at the solenoid and it would be open. I hope that's right.

[mtrans]

put light bulb in series with solenoid,if light is on than 99% is OK.

[vanbcguy]

Most of those should just have +12V all the time. They have no effect at idle at all really, it's 1800+ RPM where you will notice whether it is working or not.

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[ftm1776]

I have not yet seen 12 volts at the solenoid.....checking with my voltmeter, regardless of temperature condition.
I'll keep on probing around. There must be some sort of relay that sends 12 volts though the red/black wire to the solenoid and it should be controlled by a temperature sensor.

[burn_your_money]

put light bulb in series with solenoid,if light is on than 99% is OK.

Parallel would probably be better. Hook it up on your dash somewhere temporary and see if it ever comes on. I've never owed a car with that style before so I don't know anything about it's specific wiring.

If you don't see it coming on, tee it in with the stop solenoid and see if there is any difference. If there is, leave it teed in, if not then leave it unhooked.

[vanbcguy]

I think he's meaning if you put the bulb I'm series it will confirm that the solenoid is operating. Ie that it doesn't have a broken wire internally. More of a test light than an ongoing display.

With regards to not seeing 12V, remember it is emissions logic. God knows what was supposed to control it, if whatever that was is still present and whether whatever that was is operating correctly. Try just connecting 12V to it and driving.

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[ftm1776]

I am the original owner of this vehicle and I don't remember removing any emissions components.

As stated, this pump has recently been completely rebuilt by a reputable diesel specialty shop that focuses on diesel injection ONLY. No other car or truck repairs. I'm going to go in and ask them about it. Of course, they can't speak for anything but the pump. I know that the solenoid is not energized when the engine is cold....haven't check it hot though.

I'd like to get rid of this gadget and the silly altitude compensator and the power steering and the power brakes.....I want it simple !!!, but will have to prioritize my modifications and take care of necessary things first......maybe an old Rabbit diesel.....why did I get rid of my 78 D ??!!!

[TylerDurden]

Sometimes it's better to keep things working in the original config, or they get problematic... like parking brakes.

The ALFB is nice since it stops the IP from retarding when cold.

The altitude compensator is good since it can reduce EGTs in the mountains. It would suck to have those parts get sticky or binding from lack of action, since they affect max fueling.

[mtrans]

I think he's meaning if you put the bulb I'm series it will confirm that the solenoid is operating.

Right on,I`ll like to know if you use swich to operate this,what you get.

[Toby]

Try putting 12v to the solenoid when its running and see if there is a difference. I had a Volvo 6 banger diesel and it ran like crap with the wire off. Just fine hooked up. It made a significant difference at idle as well.