All,

After piecing together the required parts for the CAC install, I got it done this last weekend. I've got a few more things to do but wanted to ask a few questions about what I've got. I'm not quite sure what the "expected" response from the truck is, so hoping to gain some knowledge here. Gas power-adders I'm plenty familiar with but wading into the diesel end has me just wanting to confirm suspicions. As for the reason for the IC (since that's also a debated topic), this is my towing truck. Recently while lightly loaded (4-5k) through the apalacia, I was pulling out of throttle down to about 50mph or so to keep EGTs at or below 1300, and that was on a relatively average 80*F day. Now I'm not expecting to fly 75mph up a 10% grade with this truck but I'm doing what I can to make it better at what it's doing.

As of now, the truck has an 6637, oil HPX from riffraff, the full CAC kit using Carson Stauffer pipes, a 7.3AL intercooler, and Riffraff boots + t-clamps, and the 6L trans cooler. That's it, nothing more, no tuner, nada. My intent was to do the mods incrementally, while tracking EGTs, Trans Temps, while towing, etc., and the end-goal was to compare results after each mod to see what the effect was. I totally understand that you have to balance the system and its a sum of its parts. I'm also not a fan of changing 18 things at the same time so that's why I initially chose the route I did and that may be a contributing factor to my question, just being honest

My question is that after the install, I've got what I would consider "more than expected" turbo lag. Rolling into the throttle the truck seems normal but if at any point I floorboard the pedal, it'll fall on its face while boost loads and then it'll light the turbo and it pulls as expected. During the install I did relocate the MAP line to the hot-side. All of that being said, I already have a hydra and downpipe on the way. I know the OE downpipe is doodoo and needs to go. I'm suspecting my issue is related to the stock ECU still fueling like it doesn't have all this extra air volume to move now. All of my turbo experience is on gas engines with waste-gated turbos, so I'm not well-versed with how timing (via a non-stock tune) can impact my lag issue.

Additionally, I'm going to get some PVC ends to pressure test from turbo-inlet to the manifold and just confirm if i don't have (or find any) boost leaks. From reading around, it seems the tune should help. Additionally, I understand the PSDs have a .84AR + wastegate, so folks also recommend switching to a 1.0AR turbine housing to also help with the lag. Is there anything else I should be looking at to hunt down issues and/or pursuing to improve my situation? thanks for your input!

Here's a video of what I'm experiencing:

 

No wastegate unless you upgraded your turbo

is your EGT gauge calibrated? and where is it located?
do you have ext leaks or CAC leaks?
fuel pressure?
engine oil full? mine gets weak when low


my 95 with no mods but a downpipe towed 10k with out issue and EGTs were under 1250 on a hot summer day

 

Agreed. Comment was with respect to the newer PSD's have other changes (like the turbine housing) that affect lag.

I never calibrated the EGT probe myself but I'll leave that to autometer. It's located in the drivers side exhaust manifold, where it should be. I did a mirror check on the up-pipes and they appear fine but no way to tell for sure unless they're pulled off. As mentioned prior, I'm testing for CAC leaks tonight/soon. Truck ran and boosted like normal prior to the CAC install so i have no reason to believe things are having issues, other than potentially elevated EGTs. From what I've read though, the stock downpipe is likely the contributor to that and what I was seeing was pretty typical.

I've also got a cable coming for forscan, which i needed anyway. Going to do some general checks with that and ensure i don't have any codes (no light but that doesn't mean everything) as well as logging to see what everything's doing. Make sure pressures are right, etc.

 

Stock turbine for the TP38 is a 1.15, non wastegated. 1994.5-1997 trucks.

I would check for boost leaks as you have sorted. Start it cold and put hands around the uppipes into the turbo flange adapter, you will not get burned if you work fast. Odds of them still sealed after 25 years is pretty slim. Do the same for the manifolds, it seems the driver side rear (No 8 as I recall) has the highest propensity to fail and create another preturbo exhaust leak.

Sounds like you have an automatic, the stock converter is pretty lame if you still have that in there. Too loose.

 

Yup, and I've consistently seen the 1.00AR upgrade as a common upgrade for the OBS trucks. After finding out the later 7.3's are 0.8x with the wastegate, it made sense. Also yup, auto. Eventually the converter will get changed but the truck's only got 62k on it so I'll wring it out a bit first lol. I'm not planning on pulling 15k, mainly enclosed trailers with a single car + supplies (somewhere around 8-9k likely) so I'm not too worried about the trans for right now. It's done just fine in relatively flat ground (got about ~14MPG doing about 65 pulling the trailer + car from central TX to central TN already). So if I keep an eye on trans temps, the loser converter should at least be manageable, even if it is still leaving power on the table.

Also, thanks for the info on the manifolds. I'll poke around and see what I can find before I do a leak test. I knew about the uppipes but hadn't come across anything specific to the manifolds yet

 

duct tape the outlet of a shop vac to the tail pipe and use soapy water on everything pre turbo to check for leaks, no heat involved and quieter to hear leaks.

 

I swear I have read here the OE lockup clutch material is not the best on these early trucks, maybe the auto guys can tell you. I will assure you that with any spicy tuning you will be blowing right through it and it will sit at or near redline until it locks up. Maybe tuning can make it lock in second, but my concern would be shock loading on the stock input shaft on a locked 2-3 upshift. Again, ask others. I would still pop in a mild shift kit, I did two of Precision's Powertow kits last summer in 4R100s. Excellent daily driving shift feel.

Good move on downpipe, stock is junk. If you have the oxidization catalyst I would just gut it. Stock muffler I swear I read is free flow.

I have the 1.0 turbine housing, I dig it. But I also row gears so helps for relighting. Saw a dyno years back it is only restrictive past about 3000rpm. There is also a drop in S300 style turbine wheel that folks seem to like on here, I do not have it as it was unavailable when I rebuilt mine. Now with my 205/30s I plan to go with KC's Stage 1 turbocharger.

Should have mentioned the intake manifolds leak too, they are pretty easy to reseal. We are also all in agreement e-fuel is a no brainer on these trucks.

 

I had forgotten about that one but have heard it before, thanks. I have a soapy spray bottle for leak-checking various things already, as was the plan for the pressure test. I'm assuming for the test I have to set the mega-maid from suck to blow?

Good to hear. Usually the direct drum is the one that takes all the beating but i've not looked into the internals of the converter. Something i'll have to look into. Agreed for long term that it's going to get a new trans. Honestly I'm not after anything that's "big power" so I'm hoping that'll be the saving grace, really no interest in the new injectors and +180 route. Primarily just looking for a "daily" tune and then a "tow tune" with the hopes that they'll help with the shift points and get the turbo doing its thing. I'll have to dig through receipts and confirm, but the trans as-is already is a firm shifter. Certainly not the breakem-loose 1-2-3, u-joint destroyer VB that I had in my mustang one upon a time, but it's certainly firm. Does a good job of keeping things loaded on the shifts.

 

Yup stock muffler is straight thru with a small resonator chamber in the middle IIRC. once you do kitty and downpipe your opened up plenty.

I agree with these guys, check leaks pre and post turbo. MEthods listed are great

 

I did my mods in the opposite order. Did downpipe first, and ran just the downpipe for a while. Downpipe alone made a large difference in getting away from a stoplight or down an on-ramp; felt like the truck could now get out of its own way. I didn't have a boost gage at that point, but it sure felt like turbo lag lessened after the downpipe.

But downpipe is only part of your puzzle. And I also will be checking for leaks at my next major maintenance down-time.

 

I saw a dyno years ago showing the DP was good for about 20rwhp at peak, pretty solid gains for $100. Average torque gains escape me, I do know around 350-375rwhp I think it was shown a 4" exhaust would outperform the stocker (even with cat delete and DP only) in average torque gains.

 

Seemingly on turbo vehicles this is a common theme. My WRX saw a pretty healthy gain from just a downpipe and tune. Some of the new audis/VAG group cars on the other hand we don't even have to put a downpipe on because they're pretty fantastic as an OE. Just a tune on those REALLY wakes them up. I'll be interested to see what it does for the EGTs once on the truck. Reading around prior, I've found they contribute quit a bit as well.

 

Also, update on the truck. So, sheepishly, I'll admit that this was likely my own doing. After completing all the changes, I let the truck idle for a good while and then got out and drove it for about ~10-15 miles or so in varying stops, low speed, highway speed, etc. I noticed in the riffraff instructions for the HPX that in (approx) 25 miles the air should have made its way out of the system. I knew I was a little short but figured the majority of it should have been taken care of.

Last night I checked the engine oil, topped off the trans fluid, and then went for another ~15 mile drive about the same conditions. I wanted to "get used to" how the truck felt now so I didn't get myself into any trouble driving it around (ie, pulling out thinking i could scoot but it wouldn't). After that, I noticed my trans fluid was still a little low but was back to a reasonable range. Driving around too, i started to roll into the throttle and it was responding a lot better than what it was previously. Coming back home, I tried to repeat what I showed in the video and the truck didn't care, just picked up and went. Maybe a liiiiiiiiitle bit of lag but most certainly an "expected" amount, not the "boost loading" experience i had previously.

In reflection, I think it may have been a combination of air in both the oil lines and the trans lines that was leading to injectors not fully functioning as well as air in the trans lines causing lockup to not function. I remember a similar experience with putting an auto trans in my mustang, it took about ~30 miles of driving for OD to finally lock in after getting all the air worked out, etc. There's no doubt that the downpipe (and tune) will wake it up more, but I'm hoping some continued driving will work more and more out of the system and it'll be in good shape.

Thanks everyone for the input. I'll keep this thread updated after i've had a chance to get some miles in and keep adding fluids.

 

can take 100 miles to purge all air out or go up a long steep grade at full throttle

 

Well had a chance to drive it around quite a bit more and it got about as good as it would. Symptoms like the initial video would still happen in first gear real low, albeit less spool time. I'm guessing that was just from no-load on the engine, because rolling into it with a little throttle up to about 3-4psi and then getting on it showed almost no difference from before the CAC addition (in terms of spool time). In a higher gear, the change in spool time was not noticeable.

Also, I had the chance to add a downpipe and hydra, that definitely made a difference lol. Its certainly woken up, I've got some custom tunes coming but even with the PHP built-in tunes its performing much better. The +45 "daily" tune is a little hazy but not rolling coal, the "+65 fuel sipper" (it was the lowest eco-tune they had) is my new favorite DD tune. Locks up early, no haze, just enough to wake the truck up. Both from a "punch" in low gear to a "ease into it" in a higher gear the truck seems very happy.

Driving around at 65 MPH on flat and level i saw EGTs go from 730 (stock) to 540 (CAC + tune). I'll have a chance later this month to pull a lightly-loaded trailer (3k lb) so it'll be cool to see how the truck responds to that. Thanks again everyone! This was certainly a learning experience lol. I haven't spent a whole lot of time under the hood with the powerstrokes yet so this was also a great chance to check out all the fuel feeds, oil lines, etc. and learn where all of that was as well.