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Ask Juan Crespo Your Own Question
Juan Crespo
Juan Crespo, Tech Trainer
Category: GMC
Satisfied Customers: 1526
Experience:  A.S.E. Master Technician, Advanced Level, Emissions - Asian, Domestic, & European
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5.7 liter diesel starting problem1983 GMC diesel 5.7 fast glow,control

Customer Question

5.7 liter diesel starting problem
1983 GMC diesel 5.7 fast glow,
control sensor, module controlled
Submitted: 2 years ago.
Category: GMC
Customer: replied 2 years ago.
Question repeated:
Glow plugs cycle one time and shut off. Wait light remains on. Haynes manual chart points to alternator. Alt shop says Alt OK
Substituted new, plugs. new relay, new control sensor, new, module. No change. If two wire connector is removed from Alt. glow plugs will cycle 4-7 times. This effect will not repeat unless two wire connector is plugged back in and unplugged again.
Is diesel alternator different ? Observation: Alternator warning light on dash is slightly dimmer than other warning lights. Not sure
if this is normal. Grounding brown alternator wire will make light equal brightness. Not sure if this means anything.
Expert:  Juan Crespo replied 2 years ago.
Hi there. I just came online and saw your question hadn't been answered. Just clarify; in 1983 all GMC diesels came with the 6.2L engine, the 5.7L having been phased out in 1980. Was your vehicle fitted with an older engine?In any case, these vehicles require a lot of current to quickly replenish all the electrical juice these diesel engines use. So they take a 120 Amp alternator - same configuration, slightly larger than lower capacity units. I do believe you're on the right track thinking the alternator to be the cause of your problem. I'll bet your problems will be over nce the proper capacity unit is installed - as a note; alternators are there to replenish, not recharge the batteries. Make sure batteries are fully charged and load tested before installing the new alternator. Kindly accept and rate my answer now if you think the information I've provided has helped you solve your issue. Otherwise, please reply. Best Regards
Customer: replied 2 years ago.
This vehicle is a 1983 GMC Caballero which is the GMC version of the Chevy El Camino.
These cars would have come with the 4.6 or 5.7 L diesels and various starting systems
until 1984
Customer: replied 2 years ago.
I did have the alternator checked and have a multi-meter. Aware that batteries need to be fully charged.
Vehicle will start , but the glow plug system does not function properly which means winter time issues.
If you can provide some specific checks or advice that leads me to a fix I would pay for this.
Customer: replied 2 years ago.
It has been suggested to me to go to the dealer with the VIN number and buy the exact original alternator , assuming the
one on the car isn't. But after the alternator shop said the thing was OK I'm stumped.
Expert:  Juan Crespo replied 2 years ago.
Thanks for clarifying the model vehicle. The tool used to check most starting and charging systms is called a VAT (Volt and Amp Tester). Most multimeters can't read any current over 10 Amps.It appears you're not dealing with qualified professionals. What your Caballero needs is a replacement alternator rated to 120 Amps, which is available not only from the dealer, but from most retail auto parts stores as well.Were that my vehicle they're working on, I would ask them to perform a complete system test using a VAT - I would definitely go somewhere else if they didn't have that tool.Regarding the glow plug system, I would need you to elaborate with much more detail on what you mean by "does not function properly" to formulate a diagnosis (see example of symp***** *****st below). THERMAL GLOW PLUG SYSTEM SYMPTOMS No Wait Lamp (Cold Engine) Wait Lamp Pulses Slowly On and Off Wait Lamp Stays On More Than 10 Seconds Engine Does Not Start When Cold (Wait Lamp OK) Engine Runs Rough When Cold No Fast Idle When Cold Engine Stays on Fast Idle Engine Continues To Run With Ignition Off Best Regards.
Expert:  Juan Crespo replied 2 years ago.
Hi again. Just checking to see if the information I provided helped you solve your issue. If it did, then kindly accept and rate my answer now. If it didn't, please reply so we can keep working.
Best Regards.
Customer: replied 2 years ago.
Thank you for your comments. Getting back to you.
The symptom : When the engine is cold and the glow plug system is activated by turning the ignition switch to ON - the glow plugs cycle only once, turn off and stay off. The wait light remains on. The fast glow plugs are supposed to cycle on and off continuously until the engine is started. If I turn the key off and then on again the same symptom.The diagnostic chart I followed points to the alternator. A rebuild shop tells me alternator is good. The tester I am using has the following abilities I am trying to repair this vehicle myself using the diagnostic charts from the Haynes manual. I purchased an AC/DC clamp meter with the following abilities. I think it is sufficient.
DC Amps: 0-40A, 200A
AC Amps: 0-40A, 200A
DC Volts: 0-400mV, 4V, 40V, 400V, 600V
AC Volts: 0-4V, 40V, 400V, 600V
Ohms: 0-400, 4k, 40k, 400k, 4M, 40M
Frequency: 0-10Hz, 100Hz, 1000Hz, 10kHz, 100kHz, 1000kHz, 10MHz
Capacitance: 0-4nF, 40nF, 400nF, 4uF, 200uF
Duty Cycle: 0-.5%-99.0%
Diode: Diode Test
Continuity: Audible Beep
Expert:  Juan Crespo replied 2 years ago.
Since you are not answering my question regarding the glow plug system, nor following my advice regarding the type of tool needed to test the charging system, I'll opt out and re-open your question so other experts may answer. Please do not reply or the site will revert the question back to me. Best Regards.