Lost boost idk why?

3Deez · Jul 25, 2015

Hi all. First post and guess what?...I'm asking for help. A few weeks ago I swapped in a 99 1/2 engine. It ran great! I drove it today (I rarely drive it) and my boost wouldn't pass 14psi and I see zero black smoke. The only thing I can figure is maybe the fuel filter. I tried my edge evolution CTS and Bully Dog. Could it be as simple as the filter?

ToMang07 · Jul 25, 2015

Mods? EGTs?

3Deez · Jul 25, 2015

ToMang07 said:
Mods? EGTs?

Egts were up around 11-1200. Mods are just the evolution CTS or bullydog. Also put a bts valve body in the trans. Usually just use the CTS but I tried the bd today to rule that out...it's leftover from unlocking the pcm on my 2014 Ram.

Magnum PD · Jul 25, 2015

Check your intercooler clamps and your up pipes for leaks.

ghohouston · Jul 25, 2015

And check the map sensor hose

3Deez · Jul 25, 2015

Magnum PD said:
Check your intercooler clamps and your up pipes for leaks.

I did tighten everything up. I had a cracked exhaust manifold and bought a dorman. When I switched motors,I broke the dorman at factory torque specs. I got another and put a thin film of high temp silicone on the gasket because salt had corroded underneath the other one. Do you think a tiny skim of ultra copper could have failed? I don't see any soot around it. Shouldn't I see smoke from low boost?

Magnum PD · Jul 25, 2015

How are the collector donuts?

Blown262 · Jul 25, 2015

When I got my truck, it would peak at 17psi and would struggle to break 15 when hot or with the AC on. No boost leaks. My issue seemed to be my fuel pressure from the factory pump. I would sit at 58-60 idle and drop all the way to about 20-25 WOT. When the fuel in the tank started to get hot, I wouldn't see anything over 15 psi and there was a severe drop in performance. It's still a minor issue to this day when the fuel gets hot, but I have twin 45GPH pumps that are capable of peaking at 80psi. My fuel pressure doesn't go below 45 psi WOT anymore. Hopefully this helps a bit

3Deez · Jul 25, 2015

ghohouston said:
And check the map sensor hose

Hey! That thing is a little brittle and a tad loose. So if the sensor isn't seeing the boost,the truck won't fuel as much either,right?

3Deez · Jul 25, 2015

Blown262 said:
When I got my truck, it would peak at 17psi and would struggle to break 15 when hot or with the AC on. No boost leaks. My issue seemed to be my fuel pressure from the factory pump. I would sit at 58-60 idle and drop all the way to about 20-25 WOT. When the fuel in the tank started to get hot, I wouldn't see anything over 15 psi and there was a severe drop in performance. It's still a minor issue to this day when the fuel gets hot, but I have twin 45GPH pumps that are capable of peaking at 80psi. My fuel pressure doesn't go below 45 psi WOT anymore. Hopefully this helps a bit

I probably should upgrade my fuel system. I will replace the filter soon. It's not very old though.

3Deez · Jul 25, 2015

Magnum PD said:
How are the collector donuts?

Oh I left that part out too! I put the good bellowed up pipes on it. Thanks

ghohouston · Jul 25, 2015

Yeah, if the map sensor is loose, it'll cut your power down. Replace it and report back.

3Deez · Jul 25, 2015

ghohouston said:
Yeah, if the map sensor is loose, it'll cut your power down. Replace it and report back.

Will do. Thanks

Blown262 · Jul 25, 2015

3Deez said:
I probably should upgrade my fuel system. I will replace the filter soon. It's not very old though.

Well I'm no expert on these trucks. There's people here with vastly superior knowledge. Personally, I would by a threaded adapter and gauge and check your post filter fuel pressure in the bowl before spending another 30 bucks on a filter. And if your MAP is loose, I'd replace that before going any further.

3Deez · Jul 25, 2015

Blown262 said:
Well I'm no expert on these trucks. There's people here with vastly superior knowledge. Personally, I would by a threaded adapter and gauge and check your post filter fuel pressure in the bowl before spending another 30 bucks on a filter. And if your MAP is loose, I'd replace that before going any further.

Thanks. I just can't believe that slightly loose hose could do so much,but I'll find out.

Blown262 · Jul 25, 2015

Well the MAP sensor in any vehicle plays a very key role in fuel delivery. There's no mass air sensor that I'm aware of on a 7.3, so the PCM needs to be able to see, based on pre written parameters, how much air the motor is getting to adjust the fuel table accordingly. I would imagine it's more important on a diesel as there is no throttle plate to control air flow. If the MAP sees that you have a manifold pressure of 22psi, but you really have 30psi, the PCM will deliver enough fuel for 22psi of MAP and you'll go very lean as all that extra air will try to force it's way into the motor. Does you turbo and/or boost gauge flutter at the threshold?

ghohouston · Jul 26, 2015

If the map sensor hose isn't tight on both ends, or has a crack/tear anywhere in between, it can definitely cause power issues. They get old and brittle. Sometimes they're fine for a long time, and then you remove it to replace injectors, or a turbo, and that old brittle rubber cracks, you don't notice it, and you're suddenly wondering what happened. Or sometimes they do it on their own.

I had a local guy on here once with a 6.0 who did an egr delete, and couldn't figure out why he couldn't build over like 10 psi boost. I went to check it out, and in 5 minutes found his problem, his original map sensor hose "looked old" so he replaced it with a new hose, that was too big, and didn't make a seal on the intake manifold nipple, or map sensor. We tossed the old hose back on, and all was better.

Arisley · Jul 26, 2015

3Deez said:
I probably should upgrade my fuel system. I will replace the filter soon. It's not very old though.

Your stock fuel system should be fine for your truck.

3Deez · Jul 26, 2015

Blown262 said:
Well the MAP sensor in any vehicle plays a very key role in fuel delivery. There's no mass air sensor that I'm aware of on a 7.3, so the PCM needs to be able to see, based on pre written parameters, how much air the motor is getting to adjust the fuel table accordingly. I would imagine it's more important on a diesel as there is no throttle plate to control air flow. If the MAP sees that you have a manifold pressure of 22psi, but you really have 30psi, the PCM will deliver enough fuel for 22psi of MAP and you'll go very lean as all that extra air will try to force it's way into the motor. Does you turbo and/or boost gauge flutter at the threshold?

It sounds different and it reads zero psi until I lean on the throttle more than usual.