govt

Just installed a Quadzilla Commander and was really surprised to see the low turbo boost readings at low speeds. I always thought when I start to hear the turbo that I was starting to receive boost but the gauge still reads 0psi.
Thermocouple is pre-turbo installed and I can get to 17psi which still seems low. Again this is at low speeds and as power increases, turbo gets louder, boost does show up on readout but gauges are new to me and looking for feedback on what is the norm. Thanks!

CJ

Add some injectors and your boost numbers will go up. I have never liked the electronic gauges my self. I prefer mechanical. But thats just me. With just the VA5 I was getting around 22psi, not too sure how the quadzilla compares but 17 might not be too far off. Do you have a boost elbow? With the jammer III's I can get 32psi.
CJ

Tate

Boost sounds low. In stock trim, I could get 22-24 psi. Whats your EGT's like when cruising and WOT? Where is your boost sensor located? You may have a boost leak, but your EGT's will be higher.

nelrod

My boost numbers are low at low speeds, this makes sense to me but it makes me wonder if my Commander is way off on boost at top end. Mine says 38 and have seen 40. I only have Quad Race box and amsoil nanofiber drop in. Are these numbers believable? Those are at wide open throttle 3000 - 3500 rpm. And it is hauling male donkey by then.

govt

I don't have a boost elbow but I will be installing a MBRP 4" exhaust in the morning. Bought some upgrades (Xzillaraider, Commander and MBRP exhaust) so my weekend is full of trying to see what the upgrades are doing to my truck. EGT's cruising are 400 - 600 and WOT is 800 - 1000. The sensor is located in exhaust manifold between #3 and #4. Looks like I'm not going to get over 17. Just did another run down the street.

natlchamp2k4

you have to block the wastegate with either a turnbuckle or boost elbow. These do not allow the wastegate to function as normal thus you will see more boost.

Jamie

P.S. Nice Green ExCab LB 4x4

CJ

I think Tate was asking where the boost sensor is located. Mine is a boost bolt that replaces an intake manifold bolt. But this is for mechanical gauges, not sure how the quadzilla gets its boost pressure.
In my previous post I said that with the box I was getting 22psi. That was stock(oops) with just the box I get around 26psi.
CJ

torquefan

Most 98.5 and 99 trucks I've looked at would only make 16-17 psi boost. You can adjust the wastegate actuator for a few more psi, but the computer will defuel it if over about 21.

govt

Not sure how that magic happens...just installed a thermocouple in the manifold and tapped into the map sensor. That's it!
Does the boost elbow decrease mileage?

CJ

No it just allows you to build more boost. I assume the quadzilla has a built in boost fooler. Otherwise any boost over 21-22 lbs will only cause the computer to defuel anyways. If I remember correctly you have an auto tranny and I think they have a trick with a turnbuckle that allows you hold the wastegate closed longer allowing more boost. Someone with an auto will chime in and explain it better than I could.
As far as boost and mileage. Boost itself does not affect mileage however inorder to make more boost you need more fuel which will affect mileage. That being said al long as I drive like a human being my mileage increased about 1mpg with my mods.
CJ

natlchamp2k4

I agree.......more boost will not decrease mileage, it will really wake the truck up allowing it to fuel past 21-22# boost.

Jamie

Tate

Since the unit is picking up the boost signal from the MAP sensor, a boost leak could cause lower numbers. Or the MAP sensor may be going out, giving lower readings. Have you had your codes checked?

govt

Tried to but Cummins said they couldn't talk to my computer but couldn't tell me the reason why. Just finished the MBRP exhaust install. Boost is now showing up quicker but I can still hear some turbo before it shows 1psi. Maybe this is normal?

dieselfan

yes it normal, boost sucks unless you put a smarty or some kind of decent fueling box or programmer. once you put that quadzilla xzillaraider it should shoot up to 26 to 30 with a j-hook or turnbuckle(if auto).
you can have 0psi doing like 50 something mph if you try. you only get boost when accelerating.


dieselfan

CTD NUT

No J-hook for a 99 auto - it still uses the HX35.

If 17 psi is the boost level with stock fuelling, that is still low. You should be able to hit 20 psi. One of 2 problems are likely......either the engine is losing some fuelling or has a partially stuck open wastegate (the latter isn't likely), or the MAP sensor/gauge reading isn't accurate.....I would tend to lean towards the MAP/reading be a bit off. I would take the mechanical gauge anyday....too many things in this equation to allow for some inaccuracies in the boost reading when doing it electronically.