Could it be the glow plug selonoid?

[Poorman]

Been fighting this smoky startup (bad) for awhile on my "86" 6.9 f350. I'm on a manual switch, last week I pulled the glows out and I had 5 bad ones, they were only 1.5 years old with 5000 miles on them, they were Beru. I needed to get the truck going to deliver some wood. I could only find AC Delco 8g locally so I bought 5 and put them in thinking I would do more research and order more online. Putting the 5 new plugs in didn't make much difference. I ordered in a set of Bosch 80034 and installed them last night. I was surprised that 4 of the 5 AC delco plugs I installed last week were dead but all three of the Beru's that were old were still good? I put new connectors on the harness to match the Bosch 80034"s (narrow spade) and installed them. Cycled them for 10 seconds and it fired up, smoking terrible and missing so bad I could hardly keep it running, I tried a few after glows but didn't change anything. The symptoms I've been having were much worse after installing the Bosch plugs. After thinking it over I remembered there's been a few times over the last year that I've hit the glow button and my ninth plug in the cab didn't light up, but always would on the second try. I didn't have a 9th plug in last night. Could it be that the solenoid relay is acting up? (rhetorical) Can a solenoid work but not pass on the proper amperage? Intermittently? And I think the Beru's are 6 volt and the Bosch I think are 12volt, would that put more work on the solenoid and make it more prone to failure? I'm going to replace the relay but would like to better understand what might be going on! Compression is good and if I leave it on the heater for 4 hours it starts pretty clean. THANKS

 

[Kdo58]

It could be the solenoid or even the switch, I use a warn winch solenoid ,you need to use Motorcraft glow plugs, most from Amazon or eBay are fakes.

 

[Lumberjackchuck]

Did you test your glow plug harness? Do you have a good connection to the plugs?

 

[IDIBRONCO]

You can't mix and match the Berus and the Bosch and expect good results. The Bosch plugs need a longer glow time than the Berus do. It's possible that the same thing could have happened with the Delco plugs too. I would get all 8 matching glow plugs and see how it starts. Then go on to other possible issues.

 

[gnathv]

Check the voltage drop across the glow plug relay. With a voltmeter set to dc, put the leads a the two large lugs on the relay. Have someone push the button and read the voltage. Should be less than 1 1/2 volts. If it’s more your relay is bad.

 

[Poorman]

So I tried jumping across the solenoid just to take the solenoid out of the equation and no difference, even jumped direct from the battery. The harness is two years old with new connectors to match the bosch plugs, tested to make sure voltage is getting to plugs. IDIBRONCO,I didn't mix and match beru's and bosch, I mixed beru's and delco's but only while I was waiting for the bosches to arrive. GNATHV, I will try testing across the solenoid while engaged, don't understand why it would be 1.5 volts?
I've been reading a lot tonight, a lot of what I read makes me think the bosch plugs will heat faster and a lot makes me think slower and that I need a longer glow time. In the morning I'm going to try 20 second glow time and see what happens (instead of 10). It's been said that you can't burn them out, I hope that's right. Thanks

 

[Rdnck84_03]

Yes the contacts in the solenoid can get burnt and not always make contact. With the 12 volt plugs you need to double (if not possibly a little more) the glow time.

James

 

[gnathv]

The voltage shouldn’t be more than 1 1/2v. 1 1/2v would be contacts beginning to pit.

 

[Lumberjackchuck]

I will try testing across the solenoid while engaged, don't understand why it would be 1.5 volts?

Ideally you’d want almost no voltage drop across the contact on the relay, you want it all to drop across the glow plugs in the circuit. But everything has a little resistance and the glow plugs have such little resistance you’ll have a significant amount of voltage drop before you even get to the glow plugs.

It’s just Ohm’s law, current multiplied by resistance equal voltage. So the higher the voltage drop across your relay, means the higher it’s resistance through that contact.

I do have a DC inductive ammeter, I’ve never tried reading what these glow plugs pull as far as amperage and how much variation but maybe I’ll try and report back.