If you want free power you can turn you fuel pin to the deep side and grind it down to give you more fuel. You can also turn up the fuel screw on the back of the pump. You can google VE pump mods and find alot of info and pics. Get gauges 1st so you don't melt the engine down. Please don't do it just for smoke though, that's just wasted fuel and does not mean your fast.
Being a 90' you are NON-I/C, that means you have a better chance at melting something. You have no intercooler to cool your air, you have a baby H1C that doesn't cool as well as other turbos. You also have larger stock injectors to add fuel to the fire. Also with a turned up pump you need to make sure your lift pump can keep up to feed the injection pump, so a fuel PSI gauge is important to. Gauges you need are EGT, fuel PSI, and boost. With a auto trans a trans temp gauge would be a good investment also. Gauges can get pricey easy, some can run almost $200 for one gauge. This gauge has lasted me over 2 years now GlowShift | 3 in 1 Multi Diesel Gauge - Boost, Pyrometer EGT, Pressure Diesel Gauges They are cheap compared to other sets, and some have trouble with them but mine has worked great. This link has some awesome info for any 1st genner, and has everything from basic maintenance to performance FAQ/Knowledge base "How do I...?" Look here first! A.K.A. "The Sticky" - Dodge Diesel - Diesel Truck Resource Forums Read through it and you should find out alot of good info on how to get more power, and fix alot of issues you come across. Good luck.
I played with the smoke screw and star wheel on my old '90. (Two adjustments for the AFC device.) Its probably the safest fuel mod because it doesn't result in more fuel *all* the time. (unlike the power screw)
That's just me though.... based on a daily-driven D250 and not towing.
I have more fuel mods on my '93 now, and an autometer pyro clamped to the column. Made me realize my generally conservative driving style is extremely unlikely to harm the '90.
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