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Daniel Wilson
Daniel Wilson,
Category: Medium and Heavy Trucks
Satisfied Customers: 5300
Experience:  Owner at DJ Wilson
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Need some help troubleshooting Isuzu 4HK1-TC fuel problem.

Customer Question

need some help troubleshooting Isuzu 4HK1-TC fuel problem. looking for advice from someone with extensive Isuzu experience.
Submitted: 1 year ago.
Category: Medium and Heavy Trucks
Expert:  Pete replied 1 year ago.

My name is ***** ***** I am a professional here at Just Answer. I noticed that your question had not received a response and thought I would see if you still need help with this.I apologize for the delay and I hope I can still assist you with this here.My info is somewhat limited on your model here but I had seen no one else has responded and would like to see if I can help here.If at any time you feel that I cannot help with this please let me know.

I see no one has replied with any help/info on this here.In some cases this can be due to the info being difficult to obtain or the correct person that may have this info may not be online.In some cases you can obtain the info you need here from a repair facility or dealer repair facility that works on this model here.In some cases another injector or two may be at fault as well here and the number 3 was masking the others.I would have the rest of the fuel injectors tested/checked to see if any more are found to be at fault needing replaced here.If these are or were checked and found to be o.k. let me know so we can continue.

If more help is needed, use the reply tab to continue our conversation. If no further assistance is needed, kindly rate my service.You can rate at any time and we can continue to work on your question as this will not close out your question.Keep in mind in some cases it can be difficult to fully diagnose or help repair your vehicle without seeing it and I work on delivering the best possible answer from what I see to work with.

Thanks Pete

Customer: replied 1 year ago.
all the injectors are actually working now. lots of fuel available, 750PSI at the common rail. Has been bled well but won't start.
No codes showing. I am wondering if there is something preventing the injectors from 'injecting', possibly a fuse or something.
Customer: replied 1 year ago.
the Isuzu dealer says that the fuel pump has to be timed, but the mechanic did not remove the vacuum pump section, so the new fuel pump could only be installed in two positions. One position generates low fuel pressure, the other generates 750PSI - we are assuming that is the correct position. no one can tell us what the minimum PSI is for engine start up.
Expert:  Daniel Wilson replied 1 year ago.

Hi Paul, My name is***** see you are having trouble troubleshooting this Isuzu engine. I wanted to chime in and offer you some operational, troubleshooting, and technical information that will help you and your mechanic. Click on this link to access the troubleshooting info.


Customer: replied 1 year ago.
Thanks Dan, I actually had that one already, plus I have the service manual for the truck, and access to all the technical bulletins on Isuzu's site...Talked to Isuzu today and they suggested we change 'all' the injectors, maybe that would fix it.
Customer: replied 1 year ago.
I bet you if i changed the engine, or bought a new and different brand of truck that would fix it too...
Expert:  Daniel Wilson replied 1 year ago.

I just thought about your scenario you have going... If you have fuel pressure on standby in the rail, no leaks but fuel will not inject for starting check that the cam/engine speed sensor is signalling the ECM for engine RPM or injection will not be enabled. I highly doubt all injectors are bad and would not go there. This now seems electrical.

Expert:  Daniel Wilson replied 1 year ago.

2007i–2010 engines will not

start if the CMP signal is lost

Expert:  Daniel Wilson replied 1 year ago.

Check both crank and cam sensors and signals

Customer: replied 1 year ago.
I just spoke with the mechanic, the only thing he has not checked yet is the fuel pressure sensor, he checked it when it was unplugged and everything seemed good, but he figures if it is defective, it might be telling the ECM that there is not enough fuel pressure (when there is) which might be stopping it from letting the injectors do their thing. He will check the crank and cam sensors, but if they were not working it should be coding right?
Expert:  Daniel Wilson replied 1 year ago.

The fuel pressure sensor is a possibility as well and no the cam and crank sensor will not always throw a code.

Expert:  Daniel Wilson replied 1 year ago.

Also an ECM software problem could be a potential problem.... I know obtaining a test ECM would likely be difficult but maybe the dealer can reflash and bench test the existing one to eliminate a potential ECM issue.

Customer: replied 1 year ago.
Thanks again, if he checks those sensors tomorrow and still can't figure it out I have to get it towed 4.5 hours East to the closest 'Isuzu' computer in the area...I am not sure if they can do that ECM reflash or not.
Expert:  Daniel Wilson replied 1 year ago.

Thanks for the update. I would call and ask if they can do it without the vehicle and on the bench. Some dealers might be set up to do it.

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