Isuzu NPR 4HE1. Very odd behavior from Zexel Cold Start Solenoid (CSS)

[fastline]

I figured I would just make another thread as I am headed in a different direction here. Per my last thread, we bought this truck not running, found the water separator to be plugged, made it run, and been working the bugs out ever since.

I realized the glow plugs were not lighting and figured it needed some, which all 4 are toast, BUT further realized the glow relay was not running and a fuse was blown in the cab. I don't have a single schematic that shows what I see here but here is what I am seeing. With a fresh 10A fuse and everything plugged in, we witness current oddly start at 3A and slowly climb to 10A or so. We stop at about 10. We really thought this was the glow relay circuit but actually chased this down as for some super crazy reason, this tiny 10A ECU fuse operates the single wire CSS on the back of the injection pump.

I know not to touch that solenoid yet, but I also cannot figure out what resistance it should have but I am certain to works! Without the engine running I can hear it move something then it returns when that solenoid loses power. With engine running, when we energize that circuit, the tone of the engine changes.

What I am trying to do is figure out the exact significance of that solenoid. I can probably power the solenoid via other means using the provided power as the coil power, but I find the entire circuit odd because you normally would not fire a solenoid with a 10A ECU circuit.

The solenoid reads around 1ohm of resistance. It could be that it is in a bind and unable to meet full stroke so pulling high current I guess. It seems to only stay active as long as the glows are on then turns off.

I guess looking for any info at all on that CSS device. Other than that, the engine seems to run great other that I believe several things were offline like EGR, timing advance, swirl control, etc.

 

[thepumpguysc]

That solenoid operates a lever that changes the timing of injection INSIDE THE PUMP for starting..

 

[heymccall]

 

[fastline]

I am just in shock! @heymccall , could you tell me which book that is? That would have saved me like 2 days! I still don't quite understand the significance of the F-14 ECU circuit for the glow system, but the glows absolutely will not fire without that circuit hot. We currently just have that CSS solenoid disconnected as it's blowing fuses.

 

[heymccall]

NSER00-ETM-C01-GMC

 

[Toddgarage]

I’ve worked on and driven this era of Isuzu for 15 years! I loved these trucks.
-correct, that’s the cold start assist solenoid. Do not adjust or remove without a game plan. For testing you can remove the power supply wire and start without it. Add 12v and hear the difference in the engine while idling.
Below is my list of common issues.

-negative battery cable corrosion. The wire itself fails. I personally like to replace it and add another cable from frame to engine.
-positive battery terminal connections on the starter motor. Lots of vibration and corrosion here.
-behind the grill is the main electrical harness connection block. It’s challenging to disassemble and clean, but it’s a common source of corrosion and electrical issues.
-there are some wiring harness chassis grounds too. But those are usually okay.

***behind the glove box are additional fuses and relays!!!
-if memory serves there are 2 relays in the upper right area of the glove box hole. My daily work truck will burn up that relay every 6 months. I believe they are related to the solenoid.

-coolant thermostats (yes, 2 of them.) When they fail, the truck can’t reach operating temperature and it’s fueling/timing rates are different. Also check the temp sensor wiring.

-clogged fuel lines, fuel pump bangs bolts, leaking primer pump. If fuel can leak out, air can find its way in. Change the spin on filter.

-boost compensator blockage. Usually the barb fitting on the engine’s intake manifold gets clogged with carbon, open the passage with a wire. Small hose between injection pump and intake manifold.

-all those little vacuum lines fail, replace.

-factory boost pressure is about 8psi.

?teach me about the swing control… is this the little butterfly valve in the intake manifold?

Cheers. Todd

 

[Toddgarage]

Cable was slightly swollen and found this failure under it. The starter motor was a little slow… also, you can see we’re the little wires started to melt together.

 

[fastline]

I’ve worked on and driven this era of Isuzu for 15 years! I loved these trucks.
-correct, that’s the cold start assist solenoid. Do not adjust or remove without a game plan. For testing you can remove the power supply wire and start without it. Add 12v and hear the difference in the engine while idling.
Below is my list of common issues.

-negative battery cable corrosion. The wire itself fails. I personally like to replace it and add another cable from frame to engine.
-positive battery terminal connections on the starter motor. Lots of vibration and corrosion here.
-behind the grill is the main electrical harness connection block. It’s challenging to disassemble and clean, but it’s a common source of corrosion and electrical issues.
-there are some wiring harness chassis grounds too. But those are usually okay.

***behind the glove box are additional fuses and relays!!!
-if memory serves there are 2 relays in the upper right area of the glove box hole. My daily work truck will burn up that relay every 6 months. I believe they are related to the solenoid.

-coolant thermostats (yes, 2 of them.) When they fail, the truck can’t reach operating temperature and it’s fueling/timing rates are different. Also check the temp sensor wiring.

-clogged fuel lines, fuel pump bangs bolts, leaking primer pump. If fuel can leak out, air can find its way in. Change the spin on filter.

-boost compensator blockage. Usually the barb fitting on the engine’s intake manifold gets clogged with carbon, open the passage with a wire. Small hose between injection pump and intake manifold.

-all those little vacuum lines fail, replace.

-factory boost pressure is about 8psi.

?teach me about the swing control… is this the little butterfly valve in the intake manifold?

Cheers. Todd

Thank you Todd! Really cannot find many people that know these trucks but a few here certainly do! I also have to resort to my own experience. The wire that feeds the CSS is a tiny 10A wire all the way from the glove box, then the relay behind that. Either that solenoid should hardly pull any power at all, or this design is complete crap! My vote is #2. I have confirmed the timing of that CSS mimics that of the glow cycle, which is 18sec when cold, my plan is to either piggy back the CSS directly in the glow circuit, or use the signal side to fire a new relay that can serve more power.

I stumbled into a near identical issue from someone else online. It's hard for me to just replace the solenoid knowing how much drama that can bring, and the fact that it still works. Run it till it smokes!

As for the 'swirl control'. I saw that in the book, and yes, it is just a butterfly that runs air in another passage to induce swirl. I figure at the least, it is missing intake air......power.....

I am 100% going to check the boost fittings today! Thank you! As I was trying to find this CSS issue, I came to the same conclusion on vac tubing. It's all toast and needs replaced.

As for power, the truck does go but IMO, something is missing. Just seems a little flat to me. I can certainly hear the turbo spool, but that doesn't mean full boost.

 

[Toddgarage]

Yea. They are low on power, but you can run them all day with your foot smashed on the throttle and they won’t quit.


The glow plug circuit has a big relay behind the drivers front tires.

If your coolant sensor isn’t working properly, you’ll also have issues running glow plugs and CCS.

I’m home sick from work today. I’ll try to remember to time how long the CCS stays activated on my truck.
And a picture of the relay behind the glove box.

Years ago, I had a direct 12v+ wire from the battery to the CCS. The truck would run really well as long as that was connected. I know it wasn’t the right thing to do, but it gave it another year-ish of service.

 

[heymccall]

I think you'll find that using the existing CSS wire as a signal to a new relay, fused at 10amp, is the best solution.
There was talk of harness plug corrosion issues above, and you may just have a high resistance connection from the computer to the CSS.

If that wire/ connection is compromised, a relay will pull the voltage down less on it.

 

[fastline]

For the moment I just installed a fuse holder/jumper from the CSS to the glow buss bar, fused at 20A. I feel pretty confident the solenoid itself has issues as I got a spec from a shop of 7.4ohms and I am seeing 1-3ohms on it. I suspect that solenoid will eventually totally burn out and I will have to make the decision to replace or not.

Getting 4 good glows in it would be great! I don't know what kind of current the glows will pull, but figuring on about 10A each. My goal is if something shorts in the CSS, I want the 20A fuse to blow first. It's certainly not 'proper' wiring, but I suspect it will die soon enough.

I did a cold start and it did what it was supposed to do, which is to stay in for about 18sec, and kick out.

 

[heymccall]

 

[fastline]

Man, the schematics would have been the ticket a few days ago....lol

Got to put about 30mi on truck today. She runs way better! Not sure if the boost comp fittings cleaning or fixing the vacuum hoses, but more turbo sound and more power.

Will get some vac hose to fix that all correctly.

Also will have to schedule time to do a valve adjust. Just don't like the ticking but I guess it could be an injector too.

 

[Toddgarage]

Yellow relay controls the solenoid.
Started my truck today, about 45 degrees here in Michigan and the solenoid was activated at idle for over 10 minutes.

 

[fastline]

Hey, for you guys that have been SO helpful with this turd, I wanted to kick back some potentially helpful info. All 4 glow plugs were bad and I suspect never replaced. The way we approach these is trying to work in our engineering mindset which is failure torque. Per test data we performed with other plugs, we found that failure could occur at 40 ft/lb (shear), but that is on smaller cross section plugs. However, we used that as a safe margin to not exceed for the moment. Tighten torque for these NPR plugs is 17ft/lb which should be safe, so there is our zone to work in.


We use a torque wrench to loosen and do lots of tapping and such to get them to let go but all took around 25-30ftlb to let go. None broke. We further failure tested the old plugs at about 60ft lbs.

Basically the process is to not approach failure torque by knowing exactly how much is applied. If they wont let go, change tactic until that amount of torque releases them. Because of the potential nightmare if they break, I feel it is worth taking this overly cautious approach.

 

[Toddgarage]

A broken glow plug, manifold bolt, injector clamp bolt…
It can take days to recover from those. Indeed, slow down and make a game plan for stuck fasteners or parts. We all have those scars.

 

[fastline]

View attachment 298386

Yellow relay controls the solenoid.
Started my truck today, about 45 degrees here in Michigan and the solenoid was activated at idle for over 10 minutes.

I got a chance to do a cold start test. Personally, I think I will add some "pre-glow" time with a key on/off before actually starting as I think it needs more time before starting.

But it does seem I need to accept the advice given here to use the power sent back to that solenoid as control power for a relay so it can run longer. The engine seemed to run good and smooth after a slightly extended crank. No biggy. But I knew that solenoid would kick out with the glows around 18sec. After that, she was smoking a bit and I really made it mad with throttle. But I did find my high idle knob is the ticket there!

I'd love to do something more professional inside the relay box but I can't get the stupid thing apart! There are open spaces for relays in there.

 

[Toddgarage]

Isuzu cold start.
-push throttle to floor
-turn key, see glow plug light
-wait…
-crank with foot on floor.
It was below twenty today. The CSS was on for the majority of my drive to the jobsite. Motor has a significantly louder sound with it activated.
check for activity for the relay behind the glove box. I take the covers off the relays and manual close or open them for testing.

Don’t forget. Your temp sensor(s) wiring and basic computer controls play a part in this thing working properly. Like I said, had a truck that had a hot wire dedicated to turning that solenoid on and staying on at all times.

 

[fastline]

Isuzu cold start.
-push throttle to floor
-turn key, see glow plug light
-wait…
-crank with foot on floor.
It was below twenty today. The CSS was on for the majority of my drive to the jobsite. Motor has a significantly louder sound with it activated.
check for activity for the relay behind the glove box. I take the covers off the relays and manual close or open them for testing.

Don’t forget. Your temp sensor(s) wiring and basic computer controls play a part in this thing working properly. Like I said, had a truck that had a hot wire dedicated to turning that solenoid on and staying on at all times.

Ha, I gotta ask what putting your foot on the floor does?

No question the CSS relay is sending to the CSS, but the CSS is just pulling more that the circuit can handle. Who knows how long it will work. I do know it is working because you can hear a step in the idle when it kicks out. Idle actually increases, not decreases.

I was unable to test the duration on the OEM CSS circuit mostly because I was cold. All I know is without question the ECM fires the CSS relay and the fault is how much power that CSS desires.

I could prob hotwire with a switch for this winter I suppose. It became quite obvious with the teary white smoke that she needed a little heat! It started to clear and sounded like a top after about 5min idle time.

It's really nothing of extreme urgency but we like to know who is "good to go" when it's cold. I really, really, really want to hack a quick way to add a grid heater. I am always amazed how fast our 3126 clears with grid heat on. Less than 30sec and she is purring.

 

[Toddgarage]

Check the windshield visor, I’m 99% sure that’s the starting instructions written by Isuzu.

The smoke makes my eyes bleed. It’s bad, I know when my relay burns up.

We have 2 of these trucks from 99-2000. If there is time tomorrow, I’ll check solenoid ohms. Might be able to get an amperage reading… hard t say.