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Old 12-04-2013, 06:57 AM
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glow plug test...or bad injector

I tried starting my truck to come home last night, in 25 degree temp. Heater not plugged in. I let glow plugs heat for about 45 seconds, then cranked engine. After about 5 seconds, engine started firing. I released key, and engine immediately stopped. I let glow plugs heat another 30-45 seconds, then attempted to start again. I cranked for about 10-15 seconds. No sign of trying to start, and tons of white smoke in exhaust. At this point I'm thinking I have to call the wife to pick me up. Let the glow plugs go for about a full minute, then tried to start again. Engine started as soon as I turned the key.
I know the gpr and at least some glow plugs work, because after about 2 minutes, the dash light get noticeably brighter. I tested the left bank glow plugs last weekend. About 60 degrees out, engine cold. I got 10 ohms on each. I understand they should be .6-2, so I'm a little confused with my results. I assume since I have a reading, they aren't bad. I didn't get a chance to test the right bank, but assume they are OK.
At no point do I get a SES light. So are the glow plugs bad at 10 ohms? Or is it common for the gpr to intermittently not work when beginning to fail? I can only tell they were operating if I happen to be looking at the dash as they turn off, and notice the light intensity change. Or does it sound like faulty injectors? Truck runs fine otherwise, I just find it strange that it won't start, then immediately turns over after try glow plugs again. It seems as if they weren't even working the first 2 times.
I plug the heater in at night, and truck starts fine in the mornings. I have no place to plug the heater in at work, and I'm not even going to bring it to work anymore since the high temp will be 10 degrees until next week.
Any thoughts or input are welcome. Thank you
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Old 12-04-2013, 10:13 AM
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I think I answered my own question. It's only 8 degrees F outside and snowing, so I was reluctant to do any testing. I forced myself to go out and check the relay. I have power at the 12v constant post. I turned the key on, and had 11.5v at the constant, and no power at the other large post (output). Checking the smaller ones, I had 11.5v at one, and nothing at the other. I kept checking all the posts until I heard and felt a noticeable click from the relay. After the click, I still had the constant, but nothing else. At this point I went inside for a while and warmed my hands.
I read a post on another forum about testing the relay, and it said with the 2 small signal wires removed from the relay, they should both have 8v. I came back out, removed the small wires, and tested them. I turned the key on, and one had 11.5v, the other had none. I still had the 11.5v at the constant, and of course nothing on the other large post. It seems to me that for the relay to operate, one small wire should have voltage and the other should have a ground. I understand that one is a voltage signal from the PCM, the other is a PCM created (controlled) ground. I don't really understand why they would both have 8v, so I think I got some bad info there. As I recall, the red one had power, the orange had none. I put them back on the relay, then went inside for a hand re-warm.
I came back out, and turned the ignition back on. I tested voltage again, and this time had 11.5v on both large posts, and one of the small posts. For some reason I think I was reading 11.5v at the ORANGE wire and nothing on the red, but I may be mistaken. It was freezing and I was rushing. I tested each post multiple times. I then switched to resistance and tested the signal wires. I think I got infinite on the red and no resistance on the orange, but again I may be mistaken. I switched back to voltage, and still had power at both large posts. I decided to try to start the truck since the relay was activated, and it started immediately.
I do have the block heater plugged in, which makes a difference. But, usually when it's "cold" out, the water temp is either half-way from the very bottom to the bottom of the "normal" range, or at the bottom of the normal range. Since it's only 8 out, the temp was all the way down, and not reading anything.
So, I do believe that the GPR is only intermittently making contact. I'm confused about the signals from the PCM, but they seem to be correct from what I can figure. I have to wait til the weekend, but I'm going to get a NAPA GPR109, and see if that solves my problem.
I wanted to re-test my glow plugs, but it was just too freakin cold for me. I may go back out a little later and check
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Old 12-04-2013, 11:20 AM
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First, I think you Do have a problem with the GPR but I don't think the NAPA one is the best choice. Recently the Western Plow relay has become popular because it's HD and cheap! (@15.00) The NAPA is neither.

The biggest, best, relay you can use is called the Stancore. There are Lots of posts about it here and a good write up here-> Welcome to guzzle's Stancor GPR replacement Mod Web Page

Next, whoever you got that 8v info from,,,, STOP Listening to anything else they have to say. They are Clueless BSers

Key ON you'll have 12v (or whatever the system has in it) on your sm Red wire. The Orange it what controls the relay, from the PCM, and has GROUND in it when activating the relay and nothing when it's not (disconnected). When both sm wires are connected to the relay you'll have 12v in both.

The real test however, is once activated, do the two large terminals have equal voltage in them. The shows that the relays internal contacts are good and can handle the 150A the GPs are going to draw.

All Here -> Troubleshooting GPR & GP's
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Old 12-04-2013, 03:40 PM
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Thanks for the info. What you said about the signal wires sounds about right. I'm pretty certain however that when I finally had power to the output post (with brown wires) I had no power at the orange wire. I don't recall the exact voltage, but I think both of the large posts were reading about the same, right at about 11.5v.
The other confusing part was the first time I tested it and had no voltage at the output. I kept checking all the different posts, then heard the relay click, and felt it through the test probes, presumably when the PCM stopped the ground. I'm not sure why I heard and felt the click if the relay had not made contact between the large posts. I guess maybe the contacts internally are burned, so the solenoid is moving, but the contacts are only intermittently allowing current. I'm still going to throw a new relay at it, and I'll cut the old one open to see what it looks like. Thanks for the western plow info, I'll look into those
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Old 12-08-2013, 05:14 AM
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I got the new relay installed. I tested the new one with the engine warm, but I was fast enough to get the meter on it, and it's working. I also had 12v on both control wires. I cut open the old one and the contacts are burned. Not as badly as I expected, but probably just right for intermittent contact. I decided to get the cheap Napa one because I wanted to replace it right away, and they are on my way home. The western one would've cost more, plus I'd have to wait for it in the mail. I'll just expect to replace it annually. I'm planning to install a LED on the dash with power from the relay output, so I'll know when it's on its way out in the future. Thanks again
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Old 12-08-2013, 06:45 AM
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If the engine was warm, you didn't miss anything

The relay never wouldn't have come on anyway (despite the WTS light, which has No Relation to the GP activation). I too have an LED on the output side of my GPR, once you do you'll see that for yourself!
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