what is the proper way of testing a glow plug relay?

 

well had a general idea so i went out and played with it have a constant hot on the large stud which comes off the battery and both of the smaller studs were hot when i turned the switch on but no hot on the other large stud going to the glow plugs should both the smaller studs be hot when the switch is on or what somebody please explain kinda new to diesels not sure how it should be.

 

Hey Country,
When the controler is calling for relay closure, the small wire on the back will have 0 vdc and the larger lug on the right should have battery - what ever voltage loss results from the glow plug current draw. Someone in a previous post said that was about a 2 volt drop. So, If you have 13.2 volts on the battery lug and the relay is closed, you should have about 11 volts on the glow plug lug. The smaller wire on the front will have battery voltage anytime the key is on.

When I was testing my gpr problems, I removed the small wire on the back of the relay (Just to be safe. I wasn't sure if putting an outside ground to the controler might cause damage) and used a jumper wire to give it a ground. When I did this I could hear the relay click, but got no voltage on the glow plug side of the relay. Thats because my relay was bad.
Sounds like for some reason your not calling for relay closure. i.e. the back wire has voltage not ground.

 

ok this is what i did i removed the back wire like u said and used a jumper wire to give it ground the relay opens and there is power on the glow plug side now. the wire is not going to ground so what do i look for now what tells the wire to go to ground.

 

anybody know?

 

The main computer (PCM) normally provides the ground for the GPR by sinking current through a solid state device. When this closes the circuit to ground the GPR is energized. If your GPR works when you provide the ground source, but doesn't otherwise there is either something wrong with your wiring between the GPR and the PCM, or the PCM has sustained some sort of physical damage.

If it is the PCM, my inclination would be to just disconnect the wire and wire in a manual switch between the GPR and ground and install it somewhere on the dash. This would be a cheap solution to a very expensive replacement, assuming nothing else seems to be wrong with the PCM. I wired a manual bypass switch into mine so that I can control precisely when the glow plugs are on. I find that even on a cold day, I can shut the GPR off within 10 seconds of the engine starting, although under normal operation the PCM would keep the glow plugs on for about 4 minutes total (if the engine is very cold, like about 25 degrees or less).

The WTS light normally goes out after about 30 seconds, but the GPR stays on much longer than the light. I find that it will start much better on cold days if I wait about a minute or more (30 or more seconds after the WTS light goes out) before cranking the engine, and it will always start within about 3-5 seconds. I know the GPR is still being activated because I wired an LED on my dash into output side of the relay so that I can tell when it is on and powered at the output terminal.

Also, you should get very little or no voltage drop across the main GPR terminals when it is energized. If you do lose several volts, this indicates a GPR that is failing. This is a mechanical relay (unless you are in California), and any voltage drop will result in internal heat being generated due to resistance across the GPR's internal contacts. Obviously, this will shorten the remaining life of the GPR even more. In other words, a good mechanical relay will always have exactly the same voltage on the load side as on the line side and any voltage drop will always indicate either and undersized relay or poor connections at the internal contacts. Either scenerio will result in heat generation.

 

well i kinda feel stupid i was told which relay to check and it was the wrong one i had been checking the relay for the intake air heater, duh. but what i did find is that the gpr is working like it should , my prob is this i get heavy amounts of smoke on cold startups and when its a bout 10 or 15 degrees i cycle glowplugs twice so they get nice and warm then try to start it it will start fairly easy in my opionin but it lopes realy bad and smokes heavy then shuts off so i repeat and fire it up again same thing it lopes and shuts off usually on the third time it will stay running and smoke very very heavly for a min or so. my questions is this do ya'll think its glowplug time or maybe my air intake heater is not working, i bought a manual from the parts store today it said the intake heater was there to warm up the incoming air to cut down on smoking on cold start ups. I probably need glowplugs but just hoping for something easier to fix. or last questions when its that cold outside 10 or 15 degrees is it normal for it to shut off like that , i work third shift so im not able to plug it in a night. sorry for all the questions my first diesel still learning.

 

where exactly is the gpr located?
and how much are they?

 

Country,
How many miles are on that truck? Isn't it a 01? I wouldn't expect to be doing glow plugs before 80 to 100K miles.
One other problem I found on my 99 was a loose Molex connecter at the valve cover. It had corroded and the pins weren't making good contact on one bank of glow plugs. I've read other posts about bad valve cover gaskets causing your type of troubles; look for heat damage on the connector or valve cover gasket around it. The wiring to the glow plugs and injectors are passed through the valve cover gaskets. I've also heard of some trucks having shorts in the wiring under the valve covers, wires poorly secured rubbing on the push rods until shorted out.

There are many posts here about how to test your glow plugs without taking things apart. I snagged a procedure for testing and replacing the glow plugs and relay but it's for an earlier model truck and wouldn't help you, other than to say you should have .1 to 6 ohms of resistance on a plug.
Some of the older trucks have two plugs on each of the covers, my 99 only has one on each cover. If your truck is like mine, the glow plug connector is located on the bottom inside of the valve cover gasket just about in the middle of the cover. The one on the left is located in the same place but it's kinda hard to get to. There are 8 wires in each plug, 4 glow plugs and 4 injectors. The inside four pins are injectors and the outside four pins are glow plugs. Put your voltmeter's negative lead on the negative battery terminal and then test each glow plug at the pins on the valve cover gasket. If you see an open or a short then that plug is in trouble. My meter is not real accurate, so I didn't see the correct ohm readings but I did see the exact same reading on each plug. Therefore, I made the assumption that they were all good. Kinda doubt they'd all go bad by the same amount at the same time. If your need pics or a detailed procedure, do a search on this forum and you'll find one. I'm on dialup this week and it's too slow for research. Hope this helps.

 

On mine, it's just left of the fuel filter. It's a round red/brown unit with two large wires and two small wires on it. Looks alot like the old Ford starter relay's. My trucks 600 miles away so, I can't tell you the wire colors right now.

Anyone got pics?

 

Your right MDB. I hadn't thought about it, just paraphrased another post. If theres a voltage drop in the circuit it would be in the whole circuit, not just through the relay. Good point.

 

As Clemzeter said, the GPR is just behind the HPOP, and just to the right of the fuel filter on top of the engine. An OEM relay will set you back about $65 to $95, either at the dealer or Napa. However, many people use the GPR from the older IDI engines, which at Napa costs app $23. I don't know what is different about them, as they look almost identical. Napa thought the expensive one may have some sort of diode or other solid state circuit in it, but it doesn't. I took my old one apart, and there is no reason based on how they are made that they should be so expensive.

I replaced mine with a White Rodgers relay from Grainger for about $22. I used this one because it seemed like a much better relay. It has silvered contacts and is rated for 100 amps continuous duty use. Also, the coil's current draw is less then 1 amp, unlike the OEM which is close to 4 amps. This may not be signifcant, but based on the fact that the PCM sinks this current through small solid state devices a lower current draw would seem to be better.

 

thanks clemzeter for all the info it was a big help

 

Hey MDB, you must be the post I read a while back. I'm going to save the relay info this time and when I go through Salt Lake next week try and get one. Theres little doubt in my mind that I'll need another one and the White Rogers sounds like a smart purchase. Will I need a part number or just tell'em white rogers 100 amp dc relay?

 

No, they won't have a clue as to what you need. Ask for part #6C017, which is their stocking number. You will need to enlongate the one mounting hole slightly to allow you to reuse both mounting bolts, but otherwise it should bolt right up.