[timbruun]

Have a customer truck in the shop and trying to figure out a no start issue.
Truck cranks like crazy but won't start unless it gets a sniff of ether.
Doesn't matter whether it was running and shut off for only a half second. Always needs ether.
When it is running, it runs fine and it will run all day until shut off.
Getting active injector current faults on all 6 injectors while running.
Cylinder cutout test works fine.
It's a 1992 7LG 3176


All this is leading me to think that the ECM is shot. Which is weird since I can connect to it and it does run.


Have not installed sight glass in fuel system since I don't think it would lose prime that fast. Plus when I pump the primer hand pump it's stiff right away.



I have checked the timing sensor. It is receiving and sending proper voltage during no crank and cranking conditions.

Any other opinions?

 

[lanwickum]

Have a customer truck in the shop and trying to figure out a no start issue.
Truck cranks like crazy but won't start unless it gets a sniff of ether.
Doesn't matter whether it was running and shut off for only a half second. Always needs ether.
When it is running, it runs fine and it will run all day until shut off.
Getting active injector current faults on all 6 injectors while running.
Cylinder cutout test works fine.
It's a 1992 7LG 3176


All this is leading me to think that the ECM is shot. Which is weird since I can connect to it and it does run.


Have not installed sight glass in fuel system since I don't think it would lose prime that fast. Plus when I pump the primer hand pump it's stiff right away.



I have checked the timing sensor. It is receiving and sending proper voltage during no crank and cranking conditions.

Any other opinions?

A bit late for me to be thinking much at all.


I would looking into cranking voltage and cranking rpm. I know it may seem to crank over great, check them anyway. I can not remember the specs what those need to be, you will have to find them.

 

[SWFarmService]

Check all battery cables + all the connections on the starter.

Then if all is good check voltage on fuel shut off solenoid during cranking, if it is almost non existent chances are the ecm is toast but do not and I will say it again do not check untill you have verified all battery and starter connections are good and not just look ok

 

[w-mFarms]

A bit late for me to be thinking much at all.


I would looking into cranking voltage and cranking rpm. I know it may seem to crank over great, check them anyway. I can not remember the specs what those need to be, you will have to find them.

its electronic, i'm just thinking where'd come from. We had it with one of ours it never opened up the fuel pump by itself.

if it keeps prime by handpump than that won't be your issue.

 

[amos]

I have a 96 truck with the same engine. It did this to the previous owners (I worked there for many years) and we would just change the fuel filter and it always started after that. Spent many $$$ trying different things at the truck repair places, and always we just changed the filter and away it went. I just change the filter every year when I change the oil in it since we bought it and we have not had a problem with it.

 

[timbruun]

Cranking voltage is fine as well is rpm. Also checked the rpm/timing sensor and it is sending out proper voltage during no crank and cranking .


All battery cables are fine. As well as wires going to and from the ECM that have been tested so far. No opens, shorts or high resistances to be found.


When the owner bought the truck we did a complete service on it and nothing changed.


I am going to finish troubleshooting the injector faults today. Then check for fuel issues anyways. Hopefully find something that is cheaper than a new ECM.

 

[Don Boles]

Hopefully find something that is cheaper than a new ECM.

I imagine but it's the only thing that fits.

 

[SWFarmService]

Check the shut off solenoid voltage with key on and while cranking, seen this happen to two diff custum cutter service trucks in one year, I pulled my hair out trying to figure rob Hollands out, found probs here and there but both went the same way and needed ecm's

 

[timbruun]

There is no shut off solenoid on these engines. Electonic unit injectors.


So far I've pulled a bunch of the fuel system apart trying to find why I'm only getting 20ish psi during cranking and 50ish while running.


Also did more troubleshooting on the injector current faults and haven't found any problems yet.


Next is to pull the valve covers off and have a look/test the wiring under there. Possibly start pulling injectors to see if orings are the problem with the fuel.

 

[Arro]

Any chance of voltage drop while cranking that screws something up with the electronic injection ? If it's running on ether and not pulling as many amps , maybe it sorts itself out , all the best

Just re read post, see you were looking the volts

 

[timbruun]

Yea.
I'm getting 12.2 at ecm at no cranking and 8 volts during cranking which are both within spec.
More if I do both with the battery booster on.


Not getting any voltage drops anywhere so far.

 

[SWFarmService]

12.2 should throw a red flag if batteries are fully charged, take your meter on 20 volts, put it between the ecm positive and battery positive terminal to check voltage drop

The ones I repaired were about 2000 year models and were hui systems and they had fuel solinoids (been a while) I think it was slightly behind and above the air compressor, one wire with a nut holding it on

 

[timbruun]

Have done voltage drops. There is none. Batteries at time of that testing were a bit low. Charging regularily now.
Constant trying to start is hard on them.


All my voltage drops are done afterwards with a resistor as well. Similar to what a load pro would do. Tested continuity for all grounds straight to battery as well.

 

[lanwickum]

Yea.
I'm getting 12.2 at ecm at no cranking and 8 volts during cranking which are both within spec.
More if I do both with the battery booster on.


Not getting any voltage drops anywhere so far.

8 volts at cranking, I may have to look into that now, seems low to me. The only voltage that matters is during cranking at the moment. I will start up CAT sis and see if gives any specs. Will post a bit latter.

 

[lanwickum]

Says 6 volts at ECM power is minimum. Still sounds low to me.
Not finding RPM needed during cranking.
Did find an old TIB for eninge warning buzzer cause hard starts. Messes with speed/timing sensor. If it does not have a buzzer, only warning light, No problem. The check is to shut off engine monitoring mode parameter. This disables the buzzer and should start good if the problem goes away. Never heard of this one before. Only 7LG7500-up have this problem.

 

[lanwickum]

Another one, does it have 1 or 2 timing sensors? If it has 2, I think it uses both at cranking. When it is running it uses one, once it reaches a certain rpm. The ether may get it above that rpm so it will run if 1 sensor is bad.

 

[lanwickum]

A quick check. Pull engine speed sensor. If it has metal fuzz built up on it, clean it off. If it is the self adjusting gap style. Reset the adjustment by pulling out the end a bit. When you reinstall it, it will self adjust the gap. Just make sure it is not going into a gap when installing. Make sure it is against a high spot on the sensor wheel.

 

[lanwickum]

Of course, check fuel pressure during cranking.
Does it smoke when cranking? Missed if you mentioned that.
Let us know what you find.

 

[timbruun]

Agree that the voltage seems low. Just going by what SIS is telling me. Plus it is higher with the battery booster on. If I remember right is more like 10 volts.


Did not see the buzzer note. Will give that a try once I have it all together again if it still does not start.
Where in SIS do I find that?


Only 1 sensor from what I can find as well as that's what SIS is telling me.
The sensor seems to work as it should. Receives and send proper voltage. During cranking and no cranking. Also I am getting rpm reading in ET when the truck is running.
I will try get rpm speed during cranking once it's together as well. I was losing connection before but someone mention just running a wire for constant power. Not sure if that will work. Plus it doesn't sound slow by any means. With the booster on its spinning pretty good.


Also once it's together will test fuel pressure during cranking. Hopefully it's better than the 20 psi I was getting before.
Does not smoke which leads to it being electrical and not mechanical. But 20 psi is low regardless.


Noticed I didn't post this yet...I was getting 20 psi during cranking and 50 psi running. So I removed the transfer pump as well as the siphon manifold. Both look good but since I have them both off and apart I'm going to put in new relief and regulator valves along with new spring.


Would be nice if there were steps for starts only with ether in SIS...


Quick history now that I heard it from the owner. He was just backing up slowly one day and it just died. Would not start back up. After towing it home someone mentioned to try ether and it's been that way since.

 

[timbruun]

I am posting here as well to get as many ideas as I can.


3176 only starts with ether