dealing with the mechanic

[farmerpatrick]

New diesel owner here. After realizing that I do not have the know to dive into the black smoke that suddenly appeared overnight, I brought it to a shop that said "yeah we work on a lot of diesels, it won't be any problem." Now they're saying they think it probably just needs an injection pump, but they can't say for sure because "we really don't see many diesels in here." He's telling me that it has something to do with the air/fuel ratio. No kidding! So now that he has told me nothing I guess I have to pay them their 35 dollar fee and move on down the road. Any suggestions? I am mechanically inclined and have always worked on my own gas engines, but I don't want to get in over my head with a system that is completely foreign to me.
As in my earlier post, I am having black smoke under a load but none at idle or light throttle. This seemed to happen overnight.
I would really appreciate some input. I know it could be the timing, but for it to just all of a sudden happen like that? What else could it it be, and how do I check and fix these other variables.
Thanks diesel page!

[Peter J. Bierman]

First off all, get out of there!!
Second, read my answer on your first post.

Peter

[C.K. Piquup]

Are you getting good air-flow?How`s the power?I assume you put a fresh air filter on,but the fresh-air intake could be restricted.Just trying the simplest solution first.One thing for sure,the pump`s giving the fuel.

[dieselbegreat]

Yeah, get outta there! It's worth the $35 for them not to work on it further. The Haynes Diesel Engine Repair manual says black smoke under load can be caused by:
restricted air intake
nozzles
incorrect fuel (gasoline)
injection pump
high exhaust back pressure
restricted fuel line or filter
low compression
timing advanced
camshaft worn
EGR stuck open

I'd check the EGR function first. Maybe you got some bad fuel because it happened overnight.

[farmerpatrick]

Update, I got the truck out of the shop and I brought my dog and my pistol, so I didn't have to pay them the 35 dollars nonetheless. Haha. Anyways, my uncle who happens to be 800 miles away owns an A/C and cooling shop, but the good part is he employs a previous Gm diesel servicewriter. To quote my uncle "he is a crack diesel mechanic, call back at 1 tomorrow and try to be nice to him." Anyways I called the guy and he said to unplug the vacuum line to the EGR valve. Easiest thing first right? Anyways, No EGR operation and just like that NO SMOKE. A miracle, no.. just another 6.2 enthusiast that has owned and worked on them for years.
I think what happened was this:
When I first bought the truck 2 weeks ago, I was pulling 2 codes. Map sensor voltage incorrect, and EGR circuit fault. Well, the fella at Auto ZOne (which will be the death of me) pulled a MAP sensor out and the MAP code went away. Well, then I found that the line to the EGR was busted, so no vacuum. Anyways, that was probably the only problem I had and it was causing an erroneous MAP code (maybe). So now, I'm going to put the old MAP sensor back on, and hook the EGR back up and we'll see if I'm code free and smoke free.
Anyways, another point for others, is this: the servicewriter told me that noone stocks the MAP sensor, usually a special order part, so if the fella at your parts store says they got it he is probably giving you a generic gas sensor that would work on anything. That is probably part of my problem right now.
I'll try to make more sense next time.
If anybody has been through this before let me know.
Patrick

[britannic]

It's probably time to remove the EGR for good in any case - strictly for testing and off-road purposes :D ! I didn't have EGR in the first place, but I know others here know how to expunge it in a convincing manner with lasting benefits to the engine.

[farmerpatrick]

I like the idea Brittanic, I think I would like to remove the EGR for good. I'd like to know what all it will involve, what effects it will have, and what I will have to do to not always have a CHECK ENGINE SOON light. Another question, does anyone know if there are two different MAP sensors for a 6.2L, because it was something that I changed right about the time the smoke started. I understand that the EGR and MAP are directly related, so I'm wondering if maybe they did sell me the wrong part. A little research and I find that OEM, does have two different part numbers depending on what color connector you have. But all the parts suppliers have them as the same exact part??? Should I just go buy the one at the dealer? If I lose the EGR, I'm still going to need a MAP sensor.. right? Currently, I'm running an EGR code (because the EGR vacuum line is unhooked) but it's running strong without any smoke.
THanks,
Patrick

[farmerpatrick]

Quick update, I am going to replace the Auto Zone Map sensor with one from the dealer. I am getting a MAP sensor code along with the EGR code. Once I get the new Map sensor, I'll hook up the EGR again, and see if it fixes codes without getting the smoke back... I guess I'm going to have learn all about this EGR thing.
Patrick

[farmerpatrick]

I replaced the MAP sensor with an AC Delco one from the dealer, and I hooked the EGR up again, once again no codes but lots of black smoke. If I unplug the vacuum line to the EGR then I pull two codes: EGR circuit fault, and MAP sensor incorrect voltage. But with no EGR: no smoke.
Any ideas?? How should I begin troubleshooting the EGR?
Patrick

[EWC]

Is this on your 91 ? What are your codes ?

[farmerpatrick]

Yes this is my 91 6.2L "C" the codes are 32, and 33 which according to Haynes is MAP sensor voltage and EGR circuit fault. I expect the EGR code simply because the EGR is unhooked to avoid the clouds of black smoke. I messed around a little tonight with my vacuum tester. The egr valve is definitely working because you can tell a very noticeable difference in the noise at in the intake when the vacuum line is hooked up or not. When the vacuum is tested it stays around 15 inches at idle and bumps up to 20 when throttle goes up and stays there through WOT. THe Haynes manual says vacuum should be 20 at idle and 0 at 20 degrees of throttle and up. SO obviously my readings are putting a big question in my mind.
Things I'm going to troubleshoot next:
1. TPS
2. EGR vacuum solenoid
3. Vacuum pump

It seems to me that the egr valve should be open at higher throttle levels to cut down the fuel ratio and this would avoid smoke. So if the solenoid is always applying vacuum to the valve then it would always be open and then EGR wouldn't be the problem. I'm guessing it's not that simple though.
It was nighttime, but it seems to me that with the air filter cover off, i couldn't get it to smoke whether the EGR was hooked up or not. But then again it might have just been cause it was dark out. I'll play around with that theory tomorrow, and then maybe I'll just go the route of opening up the intake.

[britannic]

I searched the 6.2L forum for "egr" and found some threads for you to check out:
egr stuff (http://forum.thedieselpage.com/cgi-bin/ultimatebb.cgi?ubb=get_topic;f=2;t=002270)
egr disable (http://forum.thedieselpage.com/cgi-bin/ultimatebb.cgi?ubb=get_topic;f=2;t=002356)
egr removal (http://forum.thedieselpage.com/cgi-bin/ultimatebb.cgi?ubb=get_topic;f=2;t=002315)

[arveetek]

I had no idea that a 6.2L was ever equipped with a MAP sensor! What a deal.

I say remove that nasty EGR, discard the MAP sensor, and remove the bulb in the SES light. There's really nothing on a 6.2L that a computer can help you diagnose anyway. It's mostly just for the emissions crud that isn't needed in the first place.

Casey