First of all I would like to say thanks to ya all that post on this forum, there is some good info being shared here. In the spirit of the cold weather and all the hard cold start threads being posted I though I would share my situation. Ever since the mercury dropped below 30 my 93 idi has been a bitch to get going in the morning. If I plug her in overnight, she fires right up. I've checked the glow plugs with a circuit tester and they all test good, I've changed the fuel filter and ran some stanadyne through it along with put some in the tanks. My fuel return lines are not the grey factory ones and I believe they've been replaced in the last ten years. There are no wet spots around the filter, IP, return lines or injectors. I have the manual GP switch, when I turn the key and press the button the WTS light comes on for five secs. I then go to turn it over and after about 3-5 secs of cranking it sounds like she wants to start along with some blackish to bluish smoke rolling out the tailpipe, but once I lay off the ignition it dies, so I hit the GP switch again, WTS light comes on for a sec., turn her over and the same thing, after about the third time she starts going along with some rough idle for 2 secs. and then its fine for the rest of the day. Is this losing prime? I've read other posts about the fuel return lines shrinking in the cold and sucking air, the only difference is this truck doesn't actually get started and then dies, it acts like it wants to start, but just won't keep going until about 20 secs. of back and forth and it looks like my house is on fire from a block away. Any ideas?

 

Welcome Digler,
I think you found the right place. What you're describing is the classic bad glow plugs air intrusion problems. I don't think there needs to be any wet spots for air intrusion but someone will correct me if I'm wrong. More learned members will chime in and help with the mystery. LOL, yea when traveling and I have to cold start in a hotel parking lot I always make sure no one is in the immediate vicinityso as not to envelope them in that cloud. Good luck.

 

At first I thought it was the Glow plugs, but I tested them with the test light trick, one wire to the + post of the battery, one wire to the GP, and every single one the bulb lite brightly. I've been looking at posts by Dave S. about the GP relay and haven't quite figured out wheather or not I'm getting enough juice to the them.

 

Did you remove the connector from each plug before you tested it? I found that if connected it will light the bulb bright but when I disconnected them it was very very dim.

 

Ya, the connector was removed.

 

That's the problem with the test light trick. Even if it lights there is still a chance that under load inside it can break the connection and not heat up fully. Another words when you first hit the glow plugs on they start to warm and "grow" inside and lose the connection. does this make sense to you. Can't really think of any other way of explaining it. I had this alot on the old chevys.
The other thing that tells me you have bad glow plug/s is your time of only 5 seconds. It should be about 10 seconds on cold day if all your plugs are good. The shorter the time, the more plugs are either out or faulty connection at the terminals. The controller senses the resistance and that's how it judges the turn on time, less resistance= shorter on time.

 

The 93 new style controller uses resistance feed back to time the glow cycle.

What you may have is a couple glow plugs that are outside the optimum resistance range.

Ideal is between .5 and 1 ohm.

To give an example,
@12 volts .5 ohms resistance means a 24 amp draw or 288 watt heat source.
@12 volts 1 ohm resistance means a 12 amp draw or 144 watt heat source
@12 volts 2 ohms resistance means a 6 amp draw or 72 watt heat source

A couple 2 ohm plugs in the circuit, the controller thinks the glow plugs are hotter than they really are, so it turns them off early. (5 seconds)

So if you look at the examples for heat produced, then factor in 1/2 the normal time, you can see why you engine is hard to start.

In your example I am going to say the rough idle is the cylinders with high resistance glow plugs.
Those cylinders just don't have enough heat to fire correctly.

On the new style system, the test light is a decent fast test for burnt out glow plugs.
It was a great test for the old style 6.9 system, it used a timer not resistance.

The best test though is a resistance test.
It can pick out high resistance glow plugs and glow plugs that have shorted internally that the test light method will show as good.

But the bad thing, it usually takes a decent ohm meter to read ohm's that close to a dead short.
.5 ohm's is close to a dead short.

Digital auto ranging multi meters are the best choice for this.
I have a Micronolta meter from Radio Shack that I paid 80 dollars for many years ago and a Fluke that I paid over 150 dollars for also several years ago that both do a fine job.

With modern electronics, I bet there are cheaper meters on the market that will work just as well, but I can not give you a name.
I do know Fluke, which is a good name has several cheaper meters now.
But I can not say for sure if they are as accurate as the more expensive units are.

 

Would a clamp-on amp meter on the GP wire reflect the differences mentioned above? I have one that I use to check charging amps from a wind turbine. If so it sure would be a quick check. If not then with a multi meter the procedure is?

 

Thanks Dave, I don't have a digital auto-ranging Multimeter, but sounds like something I'll have to ask santa for. I've heard the flukes are good, would the ones sold at your local lowes (Idea) or Sears (craftsman) be suffice?

 

Fi it has a peak hold function, the clamp on meter would probably give you an indication.
But to be of much value, you would have to test each glow plug while it was completely cold.

Once it had been heated, until it returns to ambient air temp, the reading will be less.

This looks like the only auto-ranging meter Lowes has on their website.
EXTECH at Lowe's: Mini Pocket AutoRanging Multimeter

I think I would take a new glow plug to the store and tell the salesperson if it can read a resistance value on the glow plug, you'll take it.

The usual problem with cheaper meters is they just show a dead short at .5 ohm's.
So if it can read a new plug, should be very close to .5 ohm's, it should be fine.

Sear, well when you see meters in the hundreds of dollars range, yes they have one that will test glow plugs.

I see the latest version of the Fluke meter I have is 370 dollars and they don't even show a clamp on meter like mine.

 

My truck will do the exact same thing. Turn the key on and the glow plug light will go out in 3 to 5 seconds but the truck does not want to start. Does the same thing as the OP's truck. I noticed a long time ago that if I watch the amp guage the glow plugs are still on for another 5 or 6 seconds after the light goes out. If I wait till the amp guage comes up before trying to start it it will fire right up. I don't pay any attention to the light anymore, just watch the amp guage to tell me when the glow plugs have cycled and then start it. I know for a fact all my glow plugs are good but for some reason the light doesn't cycle with the plugs correctly. You might check to see if your's does the same thing.

 

I've come to find out that about 10 seconds Is the sweet spot for heating with a manual switch, then again the lowest temps we've seen in my part of Georgia haven't dipped below the 20's. My truck will start after 8 seconds, but she'll stumble a bit once cranked, even after about a 3 second afterburn. She's pretty much smooth after a 10 second burn, without the need of an afterburn. You mentioned that your using a manual GP control, so you can completely disregard what your "wait to start" light may do.

If its firing right our when plugged in with the block heater, it sounds as if the root of your problems is that your not getting a long enough glow when using the switch.

 

How is your manual glow hooked up? Is it the controller still in command but only when you hold the button, or total manual control?

 

Thats a very good question............ If your not in total manual control, your definitely not getting enough time to for them to heat. Mine are on full manual. my "wait to start light" serves no other purpose but to let me know that the relay is closed, but its also just as apparent by watching the volt gage drop to about 9.5 volts. I'll probably disconnect it once my replacement push button come in, currently I'm using a single pole residential light switch to cut them on!

 

Can any body test this? Just kidding, But have never heard of this. Most that complain about the newer system have never said that the GPs keep heating after the light goes out early.