Low Boost - 12 PSI?

[BrentM]

On my 93 W250, 5.9L can't get the boost over 12 PSI.

I have boost tested through the turbo and have pressurized it up to about 25 PSI on the compressed air supply, and it holds about 22 PSI on the boost test gauge.

I have 2 or 3 tiny bubbles coming through the rubber connections to the intercooler, and when I release the airline and cap the supply, it slowly drops about 1/2 lb per second, which I have read is expected, so I don't think I have a boost leak.

Could the turbo be worn out and not up to making more than 12 PSI?

Is there anything else I should check before replacing the turbo?

Thanks in advance for any help

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[AK Bob]

I don’t know anything about the 1st Gen Cummins, so your post sparked my curiosity. Did some checking on the internet and found a few links that may be helpful.

Apparently, the stock Holset H1C fixed turbo has a peak boost of 18 PSI (see Road Block #4 in first link).

The lack of fueling is another factor in obtaining boost (see other links).

Hopefully, this is helpful, and others more knowledgeable on the first gens will chime in with their experience.

https://www.drivingline.com/articles/performance-roadblocks-of-the-89-93-59l-cummins/#:~:text=The%2520factory%2520turbocharger%2520bolt ed%2520to%2520the%2520’89-’93%2520Cummins%252C,boost%2520number%2520can%25 20be%2520well%2520over%252030%2520psi.

https://www.cumminsforum.com/threads...essure.269544/

https://www.turbodieselregister.com/...estion.273967/

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[Corkey]

https://www.dieselpowerproducts.com/...ummins-1040178

This will also help if you haven't upgraded yet.

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[BrentM]

Thanks @AK Bob for the links; the Driving Line Article is perfect.

Looks like I am not too far off on the max boost PSI.

I have a new Hungry Diesel Fuel pin and 3200 RPM Governor spring; I have not installed them yet.

I wanted to ensure I had a good baseline before making any changes.

I will install those and turn up the fuel screw and report back; thanks again for your help.

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[BrentM]

https://www.dieselpowerproducts.com/...ummins-1040178

This will also help if you haven't upgraded yet.

Thanks @Corkey I have this one https://www.thehungrydiesel.com/#!/T...in/p/440224591 and a 3200 RPM governor spring, I purchased a while ago and will be installed shortly.

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