Well i finally did a test drive of the 93 Cummins swap to my 25FT 12k# motorhome. Before I ask any questions, here's the tale of the tape:

* 366 spring installed
* deepest side of fuel pin / diaphragm facing front (turned 120 degrees)
* did NOT turn smoke, starwheel, or full fuel screw
* turned the intake air horn on the manifold facing forward
* Ford PS intercooler, with fabricated pipes from stock pipes in donor truck to fit its new home

Note: The full fuel screw WAS already at the collar in the donor truck, but I removed the collar and can go 3-4 more turns if needed. Leaving it as is for baseline marking with my gauges (did not have gauges in the donor truck).

I have the isspro tach and the 3-in-1 glowshift for boost, egt, and fuel pressure. I'm new to these gauges so I have questions on the readings and some observations:

1. The boost is very slow to build up and the highest I've seen it go is 8 psi, even at 2300 rpm when I'm going up the ramp to the freeway. Is this normal for a stock turbo?
2. The egt hovers at 800-900 when I'm cruising around 60-70mph. The highest I've seen is to almost 1100 degrees on hard acceleration.
3. I'm feeling the motorhome is not accelerating as the donor truck (which really was very responsive "unmodified"). Could it be the gear ratios? Motorhome's gears is 4.56 with 33-inch tires and the donor truck was 3.54 with 29-inch tires I think. The motorhome revs at 2000rpm when going 60mph on the freeway, and for reasons I don't know it also revs 2000rpm when I gently accelerate and cruise at 70mph. I'll be installing 4.10 axles soon.

One nagging question: How do you guys check for intake/intercooler/turbo-boost leaks?

Thanks in advance.

 

Yessir, your boost is low. Even a bone stock truck should see 15 psi, + 5 or so. The good news is that your EGT's are right about where they should be. For checking boost leaks, I idle the engine and take a can of ether and spray SMALL shots on all connections/hoses/IC etc etc. If the idle jumps up, you've found your leak.

Not sure about the gear ratios, but I'd say that could well be the cause.

 

I made a device out of simple cheap parts that clamps on to the front of the turbo, in place of the air cleaner duct. It allows you to pressurize the whole boost system with regulated shop air and listen for leaks. I've used it successfully on dozens of trucks and I'm sure glad I made it. There's a picture in my gallery.

The main body of it is a 4" x 2" Fernco plumbing adapter available anywhere.

 

Sounds like the converter might be slipping some where are you taking the trans temp from and how hot does it get?

 

Is the AFC boost line intact? Are you getting full throttle travel?

Sounds most like a boost leak. EGT's are a little high for cruising.

 

Cool tool

How much do you set your pressure @ ?

 

Thanks!
Usually around 20 PSI, to a maximum of about 30. Right around the pressure range that the turbo normally makes.

 

Update on this, but out of topic.

I found out that the brakes are dragging. That explains the unresponsive issue, and also the high egt at cruise, and even the TC slipping suspicion. The hydroboost for some reason is applying pressure to the brakes on all wheels on its own, even at idle. And that's why also my brake lights are stuck on all the time.

But that doesn't explain the low boost. As for right now I'm troubleshooting the hydroboost problem so I can continue to test drive it.

. . . And yeah the AFC tube is intact and throttle linkage connected properly. I'm getting a lot of RPMS from this engine, just not a lot of go.

 

I have a similar problem on my carhauler.
Except for the brake issue, it's what I'd expect from a 9,000 pound rig with 4.56 gears and UNTOUCHED fuel settings on the injection pump.

4.56s with an auto would tear me up.

Mark.

 

Hey check and make sure that the electrical side of things is good as well.

I had an overvoltage problem on my 91 D350 and it caused sluggish responsiveness and the boost to stay low (i.e. less than ten).

Fixed mine by changing out the voltage regulator with a stock mopar and also adding some grounds (from the voltage regulator to the block, block to chassis, etc). I also cleaned and put anti-oxidation paste on all of the connections under the hood. Check your main engine ground as well to make sure that it is clean...

Might be a long shot.
Just my two bits

Andy

 

Welcom to the forum.

Thanks for the suggestions. I will certainly do so.

 

Problem solved.

I fixed my hydroboost braking problem this morning so i was able to resume troubleshooting the low boost issue.

Before i did another test drive, I double-checked all my hoses and pipes and they were on the very loose side of things. When i installed the IC I know I babied them rubber hump hoses for fear I could pierce them so i tightened them finger tight, OK two fingers tight. In fact, the 3.25 to 2.5 rubber adapter at one side of the IC was off the IC - it was ajar with a loose clamp. So I tightened all the clamps as if I didn't care if they pierced or snapped (since they're just for prototyping. I'm gonna replace them with silicone ones).

I drove it for 40 minutes and here are my new observations:

1. I couldn't wipe the smile off my face (well that's my wife's observation)
2. The boost climbs reasonable well now to 10 psi easy on ramp to the freeway;
3. The EGT now hovers around 550 cruising at 70mph and 2000rpm.-8
4. On an intentional hard acceleraration, I was able to make 22psi at 2500rpm, and 1000 egt. I didn't want to push it harder - I was already going 85mph.
5. and oh my fuel pressure gauge, for some reason, is now showing lower pressure (5-7 psi, used to be 6-8)

The one thing I wish it does is take off / pick up speed with a lot less rpm, from a dead stop. I don't understand why it has to go all the way to 2000rpm (noisy) before the rpms drop and the engine quiets down. The donor vehicle didn't used to do this, of course there's a big difference in weight (5K# truck VS 12k# motorhome) and the gearing (3.54 vs 4.56), (note: my tps/potentiometer is set to 0.70 volts)

What can I do to allevaite the above issue (other than putting on my 4.10 gears)?

And the new observations, are they pretty normal this time? If so, I'm ready to mess with the starwheel and/or the full fuel screw. Which one should I mess with first?

 

May I use the ether cans found at Home Depot or lowes?

 

Start cranking on that fuel screw. You really won't be able to wipe the smile off. Use the starwheel and smoke screw to fine tune to your liking. I think your rpm issue is a combination of the added weight, stock torque (non)converter and the gearing.