Can ECM diagnostics be ran with it off the truck

We hooked it up to the computer and erased all “historic” codes. He eliminated the vehicle speed parameter(70mph) and we drove it. Started down the road, rpms were going higher than 1800rpm prior to each shift, just to show him, that it would probably drop back down in 9th or 10th. Got it up to 10th, truck was at 77mph and then rpms dropped to 1800. Went back, checked for codes and VSS, showed up. Codes 35 and 54, both related to vehicle speed sensor. So, I’m gonna go get a new one tomorrow and try it.

 

This plug has 2 wires per plug and 2 plugs. How far do I screw this sensor in and lock it down?

 

I have only ever encountered 2 legit failed ECMs and one failed because it was full of water due to external damage. There's a reason ECM replacement is the very last step in every troubleshooting procedure.

 

I would not send the ECM out. If you've got a harness or sensor issue you won't see it with the ECM out of the truck. The fact ECMs are generally very reliable it'd most likely end up being a waste of your time and money.

 

It's often looked at as a last resort or just poor diagnosis and it doesn't fix it. Kind of like throwing a harness on because the "tech" can't (or doesn't know how) to find the problem wire or sensor. Ironically, usually the problem remains.

I watched a guy replace a harness on a forklift recently. The problem was someone installed an incorrect relay in the box. So the problem still remained after 8 hours of labor at 140/hr plus 3500 for the harness. A relay costs a couple dollars.

All the while these shops try to force their incompetence on the customer.

 

I think those get twisted down by hand until they stop. Then, back it out about a quarter inch or so. Maybe a couple full turns then lock it down.

 

Well, I got no problem admitting my ignorance, about some things. On, the other hand, I didn’t quite expect the one mechanic I talked to, to immediately suggest converting it over to a DDEC4(harness, ecm, injectors).

 

I hope you didn't think I was referring to you in my previous statement. Just referring to some of the halfass mechanics in the industry that won't take the time to learn something new or keep up with industry developments.

I didn't know you could convert to an updated system. How nuch did he say it was going to cost? Did he guarantee all your complaints would be resolved 100 percent? What are the advantages or disadvantages to changing over?

 

Naw, I didn’t interpret it that way.
He didn’t elude to what it would cost to convert but did say it used to be offered as a kit. It was everything I mentioned and also, drilling a port into the intake for some kinda sensor, that the DDEC4 has. Before, I grill the guy, he did suggest plugging it up and testing for codes first, it’s just that he was 2-3weeks out. I think that a little rediculous considering the guy who did test it, had it diagnosed it 15 minutes. Maybe he was just giving me a “worst case scenario”?

 

You need to find mechanic who can do advanced diagnostic to read what cause the limp mode. Also some words about your truck, year, transmission, advanced ABS?