Clicking Glow Plugs?

[wmoguy]

When I flick the key to "on" the wait to start light comes on for about 2 seconds then I hear what I think are the glow plugs clicking non-stop until I start the truck. If I watch the volt gauge it bounces down and rebounds with every click.
I bought a new GP relay to install this weekend and have 8 new GP's sitting in the garage. Do these issues sound like plugs and/or relay or is it something else?
Also, anyone have some good instructions for replacing the GP's and relay? Pretty pictures with instructions are greatly appreciative

TIA fellow OB's!

 

[mabc926]

Sounds like the relay.

 

[SparkandFire]

My truck did this with two bad glow plugs.

Changed out the bad ones and now the WTS light is on 10 seconds or so, then the truck fires right up.

The newer style relay actually shortens the glow time significantly if it senses less than normal current draw (to protect the remaining GP's from overvoltage) It pulses like that as a way of trying to tell you something is out of whack in the system (similar to how a blinker circuit works, if one bulb burns out the other one flashes very quickly)


Ohm out each GP individually, you should have less than 3 ohms per plug to ground.

 

[Compu Doc]

Sounds like the relay.

No it's not the relay just some bad glow plugs. If the OP bought all new Motorcraft/Beru plugs then change them all out. If you bought Autolite's or Champions or some other brand do not install them and return them for Motorcraft.

As for instructions carefully remove the negative battery cables and then the glow plug wire from each plug. It can be done all at the same time or each plug wire can be removed individually. Take the appropriate size deep socket and gently unscrew the plug. You should be able to do it with a 1/4: drive ratchet. If you feel any resistance to the plug coming out grab a can of PB Blaster and spray the exposed threads. After you do that screw the plug back in and repeat the process until the plug comes out easily. The PB Blaster will work it's way in and eat any carbon on the tips that may be hanging up the plugs from removing easily.

Take your time and do not rush. After you replace all the glow plugs with Motorcraft/Beru plugs then reconnect all the GP wires and then reconnect both negative battery cables. Turn the ignition on in the truck and see how long your wait to start light stays on for. After it goes out start the truck.

If the wait to start light is the same as it was before on a very short cycle then replace the controller. Their is no need to replace the controller if the time increases when the new plugs are installed. Also you should no longer hear a rapid click of the controller after the new plugs are in.
If all works well after the glow plugs are in put the glow plug controller in a safe place where you will not forget where you put it because although you did not need it today their may come a day when you do.

 

[Diesel JD]

It's very likely you just have a bad glow plug or two. As stated motorcraft/beru ZD-9 are the preferred brand(much preferred) over any others. Autolites and champions are definitely a bad idea with this system. Find your bad glow plug, figure out what brand it is, if it's a Motorcraft just switch it out, if it is autolite or champion then you should replace the whole set if you can afford to....and it's good insurance because they tend to swell and stick in the head when they burn out. If they are Bosch, AC, SLM/LDM, Delphi etc, then it's a judgement call. They usually don't ruin engines like the bad brands do they just don't work as well or last as long as the Motorcrafts do. In any case you should not mix brands. The ohm test is the correct test for the 87 and later system but in reality bad glow plugs are usually opens so a light bulb (not LED) test light will find them. If you don't find any opens then any plug that differs significantly from the others is probably the bad apple or if you find different brands. Proceed with extreme caution if you find ANY resistance once you have unthreaded the glow plug as CompuDoc indicated. If you force it you could be left with the difficult decision of risking engine damage by hoping the engine "passes" the glow plug tip or pulling the head. Not good choices so be careful and post back before you act if you have any questions.

 

[mabc926]

I was way off, my truck has the 6.9 style GP system so that's always the system I think of.

Anyways, if you're getting new glow plugs check out rockauto.com they have about the best prices around.

 

[wmoguy]

Thanks guys! I bought a set of gps when haul had that sale in January. They are Bosch plugs. I think I will attack this project this weekend.
While I am under the hood I think I will turn up the pump. I am pretty sure it's less than stock cuz it feels weak and has ZERO smoke even if I lug it Can someone post the link to the article on doing this? I did a search but didn't score

 

[OLDBULL8]

If the wait to start light is the same as it was before on a very short cycle then replace the controller. Their is no need to replace the controller if the time increases when the new plugs are installed. Also you should no longer hear a rapid click of the controller after the new plugs are in.

That is the wrong information to give someone uninformed as to how GP controller's work.

From 1983 to 1986 6.9 engines, glow plugs should only be on for 5 seconds or less as they are 6VDC plugs and energized with 12VDC or they will fail prematurely, they are a ZD6 glow plug.

From 1983 to 1987 an electronic controller should NOT be used, it's better to have a manual push button to operate a relay and held closed for not more than 5 seconds.
If you have changed over to the PTC Positive Temperature Co-efficient glow plugs, then an electronic controller can be used. http://www.oilburners.net/brian/idi/FordGPretrocombo.htm


From 1996 to 2003 the cycle time is controlled by the engine oil temperature thru the PCM, they are a ZD11 glow plug.

From 1988 to 1995 the cycle time is controlled as below.

The Zig Zag Chromalox strip hooked to the relay and then to tha GP wires is used for current rush control, it should always be there.

All the GP controllers made since 1988 to 1995 have a thyristor incorporated in the electronic circuit. It senses the ambient temperature and tells the controller how long to stay on, they are ZD9 glow plugs and are 12VDC plugs.

A GP controller will stay on from 0 to 20 seconds depending on the ambient temperature, the thyristor sets the cycle time. If all GP's are good then the controller will turn on for that length of time, then the controller will cycle ON/OFF for up to two minutes to keep the GP's glowing after the engine has started.

ZD9 glow plugs pull 18 amps each to glow then back off to 15 amps each when hot for a total amp load of ~144 to ~120 on the cycle start to finish. With good batteries and GPC relay, the voltage will drop to no more than ~9 VDC then return to ~12.6 VDC. from beginning to end of GP cycle.

 

[Compu Doc]

The OP has a 1993 truck. His GP light stays on for two seconds now cold. So if he were to replace the GP's on a cold engine and the light still went off after two seconds after replacing the GP's on the same cold engine that has not been started how is that giving him bad information?.

When I bought my truck 10 years ago the GP relay clicked the WTS light was on for two seconds before clicking. After replacing the GP's and having three bad ones after testing the old ones after they were out and the others replaced my WTS light stayed on longer and the GP relay did not rapidly click anymore.

I don't think that the OP was looking for information on how the GP controller works (although it is good to know) he was asking if the problem was the GP relay or the GP's. He has both all 8 new GP's and a new controller that were not installed yet and the controller may not have to be installed as I said in my original post.

 

[wmoguy]

G Plugs replaced

Well that went relatively easy! No stuck plugs, not broken tips (thank you lord!)
The plugs that were in there were Autolite plugs, they seem to be pretty bad. See pic below.
Now with the new Bosch Plugs in, I get about 10-15 seconds, and i can hear a slight humming noise, like things are workign as they should. Then the wait to start light goes off, that clicking starts. If I start the truck that clicking continues for about 15 seconds, in which during that time you can watch the voltmeter bounce up and down rapidly. Sound normal?

 

[Compu Doc]

Well that went relatively easy! No stuck plugs, not broken tips (thank you lord!)
The plugs that were in there were Autolite plugs, they seem to be pretty bad. See pic below.
Now with the new Bosch Plugs in, I get about 10-15 seconds, and i can hear a slight humming noise, like things are workign as they should. Then the wait to start light goes off, that clicking starts. If I start the truck that clicking continues for about 15 seconds, in which during that time you can watch the voltmeter bounce up and down rapidly. Sound normal?

About as normal as your going to get with the Bosch plugs. The glow plugs do stay lit after the WTS light goes on to cut down on smoke when the truck is started cold. About a minute or so (never actually timed it) they go off.

 

[romulus]

yep i had the same symptom when i first bought my truck many years ago. it had autolite gp's installed by the PO.... and they are complete junk, you see the difference in the build quality compared to the oem plugs....and they are made in germany, gotta love that.

i also replaced the relay on my controller with a starter relay. the contacts in the old relay were shagged.

starts every time with no issues at all for the last 5 years.