I've been looking for info and reading a lot on the early '90's 7.3 IDI glow plug system and thought it would be nice to have a few basics in one place with an easily searchable title.
I haven't found my answers yet so this post is to help myself as well as all other TDS users in solving their glow plug system issues without having to search thru scores of threads on users specific glow plug problems.
It will not be an all inclusive complete diagnostic and repair guide to all aspects of the glow plug system, but I will try to go a little beyond just the very basics. Sort of a text only flow chart.
Lets start with this handy reference link from cdnsarguy
http://www.thedieselstop.com/forums/f30/gp-controller-how-works-271828/
"My truck is hard to start, is it the glow plugs?"
To decide if your GP system is working correctly or not (and the hard start is not fuel related) we should start by answering these questions.
1. Are my batteries fully charged, and supplying adequate amps for cranking/starting.
If not, first check alternator output, then have batteries load tested.
2. At temperature "X" my WaitToStart light stays on for "Y" seconds for a cold start [without block heater].
.........(need table of values here)...........
If your WTS light times are not within a couple seconds of the approximate times at a given temp.
a) Check for bad connections at glow plugs. May be broken, rotted or just disconnected.
b) With a cold engine remove wires at glow plugs and check resistance. They should all be 1 ohm or less. If not replace as needed, or remove and inspect all for burnt/swollen tips (replace all if they're autolites )
If GP's ck OK then the glow plug controller and relay are next to check.
1) Look for bad relay connections (loose,burnt,dirty), or bad controller ground wire.
2) Check voltage at large relay terminals. GP side (ribbon resistor) voltage should be the same as hot battery side with key "ON", and relay energized (WTS light is on). Lower voltage =weak/bad relay. No voltage =bad relay or relay trigger wire (white wire on small terminal) circuit issue, check for battery voltage there when key is turned to "ON".
If relay is bad, it can be purchased by itself, or with the controller as a unit.
If relay ck's OK the controller can be faulty, but is not really testable separately, either it cycles GP's or it doesn't.
3)The wiring harness to the glow plugs is another possible issue and can be checked by 1st disconnecting wires at all GP's, Using an ohmmeter check for continuity from each wire end to terminal at bottom of ribbon resistor on relay where harness connects. Or by connecting a jumper from "hot" side of relay to bottom of ribbon resistor harness connector, then using a test light, or volt meter from each GP wire end to ground.(The WTS light will come while this method is used.)
{Use of a battery charger me be needed for extended testing of the GP system to maintain appropriate battery voltage levels.}.
This thread is a work in progress, sort of a "wiki" or possibly a potential "sticky" on the subject I suppose. As additional info is posted I will edit this original post without quoted attribution for ease of future viewing. All replies will obviously be in the thread below.
Thanks in advance for any contributions.
Some questions for completing this post.
1 A short table of approximate seconds of glow time @ various temps.
2 What sensor does the GP controller use to determine temp? integral or?
3 What voltage should be reaching GP's, 9-10?
I haven't found my answers yet so this post is to help myself as well as all other TDS users in solving their glow plug system issues without having to search thru scores of threads on users specific glow plug problems.
It will not be an all inclusive complete diagnostic and repair guide to all aspects of the glow plug system, but I will try to go a little beyond just the very basics. Sort of a text only flow chart.
Lets start with this handy reference link from cdnsarguy
http://www.thedieselstop.com/forums/f30/gp-controller-how-works-271828/
"My truck is hard to start, is it the glow plugs?"
To decide if your GP system is working correctly or not (and the hard start is not fuel related) we should start by answering these questions.
1. Are my batteries fully charged, and supplying adequate amps for cranking/starting.
If not, first check alternator output, then have batteries load tested.
2. At temperature "X" my WaitToStart light stays on for "Y" seconds for a cold start [without block heater].
.........(need table of values here)...........
If your WTS light times are not within a couple seconds of the approximate times at a given temp.
a) Check for bad connections at glow plugs. May be broken, rotted or just disconnected.
b) With a cold engine remove wires at glow plugs and check resistance. They should all be 1 ohm or less. If not replace as needed, or remove and inspect all for burnt/swollen tips (replace all if they're autolites )
If GP's ck OK then the glow plug controller and relay are next to check.
1) Look for bad relay connections (loose,burnt,dirty), or bad controller ground wire.
2) Check voltage at large relay terminals. GP side (ribbon resistor) voltage should be the same as hot battery side with key "ON", and relay energized (WTS light is on). Lower voltage =weak/bad relay. No voltage =bad relay or relay trigger wire (white wire on small terminal) circuit issue, check for battery voltage there when key is turned to "ON".
If relay is bad, it can be purchased by itself, or with the controller as a unit.
If relay ck's OK the controller can be faulty, but is not really testable separately, either it cycles GP's or it doesn't.
3)The wiring harness to the glow plugs is another possible issue and can be checked by 1st disconnecting wires at all GP's, Using an ohmmeter check for continuity from each wire end to terminal at bottom of ribbon resistor on relay where harness connects. Or by connecting a jumper from "hot" side of relay to bottom of ribbon resistor harness connector, then using a test light, or volt meter from each GP wire end to ground.(The WTS light will come while this method is used.)
{Use of a battery charger me be needed for extended testing of the GP system to maintain appropriate battery voltage levels.}.
This thread is a work in progress, sort of a "wiki" or possibly a potential "sticky" on the subject I suppose. As additional info is posted I will edit this original post without quoted attribution for ease of future viewing. All replies will obviously be in the thread below.
Thanks in advance for any contributions.
Some questions for completing this post.
1 A short table of approximate seconds of glow time @ various temps.
2 What sensor does the GP controller use to determine temp? integral or?
3 What voltage should be reaching GP's, 9-10?