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4 Wheel Drive/SUVs/1990 gmc sierra 305ci engine change


I have 2 questions, 1) concerning an engine change. Ive read that GMC produced the 305ci engine from 19772003. What I want to know is how late of and engine can I put in my 1990 GMC Sierra K1500 4X4 truck without having to modify the connections, IE where the newer engine will connect to my current computer and wiring harness. My engine, 1990 GMC 305ci, TBI, 5 speed std trans.
2) Before I bought this truck I took it into a service diagnostic shop to have everything checked out. The shop said it was a great truck and the engine was tight. The shop said the truck said that it would pass the smog test with flying colors. I bought the truck, started the paperwork with DMV and took the truck to a STAR inspection station. The truck failed miserably on everything. The truck runs like a top. The star inspection station said to take it to a repair inspection station down the street to have the truck checked out and have the necessary repairs done. The 2nd shop said I needed new heads that mine were shot & @ a cost of $1800 plus materials. I took the truck back to the original diagnostic service shop with the print out from the star inspection station. They said that there isnt anything they could help me with & that DMV had me?? I took the truck home, did a complete tuneup, flushed the whole fuel system. Changed all the fuel line to braided SS. And the Day before taking the truck back in for a retest I put in 10 gals of alcohol straight/ no gas anywhere in the system. During the retest the tech says everything looks good. Then the tech asked if I had the repairs done that the other shop recommended. I told him that I did a complete tuneup/ system flush/ oil change & that I had the heads redone. The tech call the 2nd shop talked to them and then said that my trucked failed again. I tried taking the truck to a different Star inspection station and they ask if the necessary repairs have been done. They said all Star inspection stations are linked together through DMV. I then sent an email to Bureau of Automotive Repair and explained what was going on. I never heard back from them


Wow, sounds like the repair station has something going on with the inspection station.  Not sure where you are at, but if you took the truck to a service diagnostic shop, why didn't you get a smog certificate there?  There should have been no reason to take it to a star inspection station.  In California, the seller is responsible for the smog by law.
I would try to find another reputable shop that does smog certs, and have them run a smog test, without telling them the history.  If it passes, take the cert back to DMV and file a formal complaint.  You could do a simple compression and leak down test to check the heads.

As far as what years will work with your computer, you would have to contact a shop that does this type of installations, as the specs change quite a bit depending on the year.

Check all avenues before spending the money on a new motor.


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Carl Brandt


Will discuss suspensions, lifts, lockers along with tire suggestions. Trail ratings and possible requirements needed for specific type of trails. Safety equipment and what you should carry with you. Certified off-road instructor. I am not a mechanic, and 4-Wheeling is a hobby, so if I can't answer a technical question it is due to my mechanical knowledge being related to vehicles that I have owned, or have worked on. I do not have manuals on all vehicles, and I suggest that you obtain a repair manual for mechanical problems and do some research before asking your question. Most mechanical questions can't be answered completely without looking at, or listening to the vehicle in person.


40 plus years of 4 wheeling in a variety of vehicles. At the present time, my major off-road rig is a 94 Jeep Wrangler with a spring over and a 1 1/2" suspension lift. This gives me a total lift of 7" or so. I have lockers front and rear. I have removed the track bars, and sway bar for maximum articulation. I am running a stock 2.5 ltr 4 cylinder with a Jacobs ignition along with a cold air high flow filter. It has 4.56:1 gears with a Dodge NV4500 transmission along with a 3.8:1 Atlas II transfer case. This gives me a final ratio of 105:1 in low gear/low range. Other vehicles I own, are a 96 Ford F-250 with a 6" lift, posi rear end, 36" Hummer tires, 5 speed with a fuel injected 460 ci engine, an 87 Samurai with an 8" lift, Ford 9" rear end with a spool, Chevy Dana 44 front end with an electric locker, 5.88 gears, 16% reduction in high range and a 6.5:1 low range with 35" Baja Claws, and a stock 2003 Grand Cherokee Overland. Trails I have run are the Rubicon (10 times), Dusey Ershim, Fordyce Creek trail, McGrew trail, several trails in Moab, Utah along with local monthly runs.

Lost Coast 4x4's Cal 4-Wheel Corva UFWDA Blue Ribbon Coalition

Certified off-road instructor - Certificates in engineering/electronics

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