Detroit 12.7 DDEC 4 Interesting problem

Ok. Put a mechanical boost gauge in. My scangauge which reads what the ECM sees, is way off from my actual manifold pressure. Mechanical gauge shows 30 psi. Scangauge shows 18 psi. Something is obviously wrong. What it is, I don't know.

 

Just had my injectors all set to 75 and got 2 more pounds boost and way more power. Engine harness is next when i get home.

 

This thread is getting old, but I thought I would put an update up. Still have not fixed the problem with the truck. But have it narrowed down. For some reason the ECM is reading the boost sensor wrong. I replaced the wiring harness to make sure there was nothing wrong there. But either there is a table in the ECM that is wrong, or something. So far everyone I talk to says the ECM tables are all the same. But basically the problem is, is that when I am building 30 psi of boost the ECM only reads 18 psi. So it only adds fuel for that much creating a constant lean condition. I have talked to more so called experts than I care to think about! And none of them have an answer. I'm basically down to rebuilding the ECM. But the problem with that is, that if the rebuilder uses the program from my computer, I will have the same problem. So why spend the money and rebuild it when I can't see it fixing the issue? So I am just waiting and driving it until I find someone who understands the problem and isn't just a parts changer.

 

It takes fuel to.make boost, if your making 30 psi you have fuel for 30 psi. Your not running lean.
Are you sure your scan Guage reads absolute boost or ecm for that matter?
Is it posible that you have to add the atmospheric presure on to the ecm or scan quage readout.
Depending on your elevation your atmospheric presure could be any where from 10-14.7 psi.
Now add that onto your 18psi and bam! Now you got your true boost reading.
Get it out of your head that diesels run lean, they make boost with how much fuel they have. These are not a gas engine.
Also you are running a non wg turbo, so your boost is a direct result of your fueling not a stuck waste gate.. personally I think your over analyzing things and it's running fine.

 

Scan gauge reads a different value then what the gauge shows ECM doesn't always use the same psi reading as the gauge according to what I read before somewhere Just googled it ECM can also read in inches of mercury which is close to double the psi the gauge shows

 

speaking of fuel to make boost.... have you checked fuel pressure? upgrading to a bigger turbo usually doesn't do much except bring egt down a bit unless you add more fuel..

tge extra air the turbo puts in does nothing if there is no more than normal fuel in the chamber.

 

You're assuming a bit here.

1) You're assuming the engine is running lean. I assure you it is NOT. The only thing that might possibly be out is timing and it wouldn't be a huge amount. If the truck is running fine, it is fine!

2) You're assuming the scangauge is giving the reading that the ECM is seeing. The scangauge is a very generic device. It gives goofy readings all the time depending on which truck it is installed. The only real way to check it is to get a shop that has DDDL hook up to the computer and go for a drive.

Don't goof with the ECM
Don't pay any more money on this
Don't do anything until you've checked #2.

You're assuming the truck isn't right, when it could just be the scangauge.

 

I read this and wonder where you figure 40psi from? If you have a larger turbo producing a greater volume of air psi will be lower and still getting more air. Psi is only half the eqution cfm is the other. Not to mention all your electronic gauges are set programmed around stock turbo. Runs good, pulls hard and good fuel mileage is all that matters!

 

my buddys dd4 runs around 40 psi boost my dd5 runs 48 or so with the leon tune they both have 171702 on them