1994 6.5

[John D.]

I Have a 1994 Chevrolet 3500 with a 6.5 that has been changed out. My truck has "F" as the 8th digit in the VIN # meaning Heavy Duty. Will the engine out of a light duty work with my ECM? I have been told by some that it will and some it will not. Could someone confirm this and advise me of what direction to head. Any help would be appreciated.

[john8662]

Yes, if your current ECM is not equipped with an Eprom that runs the 1994 specific injection pump only on some 1 ton 6.5's starting in 1994.

Read the tag on the injection pump you have in the truck now (the original engine) and I can tell you if you can swap and put the Light Duty engine in your truck (minus the EGR intake manifold, which you'll swap out for the one on your HD engine.).

It will say DS4 831 XXXX, need the rest of the numbers...

J

[John D.]

There's the problem, bought the truck 3 years after the engine swap, all I know is the people that had the truck before me. told me it had wiring issues since the swap and had been parked. Soooooo, no old engine to look at.

[DmaxMaverick]

The "engines" are interchangeable, so it will work. The long blocks are identical, within the year models. The differences are the emission components, and some (relatively minor) electronics. If using a 1994 LD complete engine in a 1994 HD truck, the intake (non EGR) and injection pump should be original 1994 HD equipment for a non-issue replacement.

The 1994 model year is unique, in regards to the LD vs. HD models (VIN S vs. VIN F). The HD models (VIN F) require a unique injection pump, while the LD models are interchangeable with any, including later model year pumps. This is not a wiring issue, but is specific to the unique computer programming. If you have a 1994 HD PCM, you'll need the specific 1994 HD injection pump. This can be worked around with aftermarket programming or a PCM swap from a 1995 model. Depending on your local emission requirements, this may or may not create other issues.

[Kennedy]

Actually it's just the Eprom that needs swapped Mav not the ECM. The 5068 pump is the odd man out the rest all interchange. There are a lot of mismatched trucks running around out there due to swaps.

[phantom309]

My 5068 pump runs just fine on a 5521 eprom.

[DmaxMaverick]

My 5068 pump runs just fine on a 5521 eprom.

As it should. It isn't the pump, it's the EEPROM that causes the stink. The 5068 pump will work with any EEPROM. The 5068 EEPROM will only be happy with a 5068 pump. You aren't using the EEPROM that makes it unique to 1994 HD applications.

[John D.]

Thanks guys, found out that whoever did the swap did not know about the odd pump. I read the #s on the pump and found out that it was a 5521 and the ecm in the truck was for a 5068. wanting to keep the truck as original as possible I have a 5068 on order. Will let you know the outcome.
Again thank you for the info.

[phantom309]

As it should. It isn't the pump, it's the EEPROM that causes the stink. The 5068 pump will work with any EEPROM. The 5068 EEPROM will only be happy with a 5068 pump. You aren't using the EEPROM that makes it unique to 1994 HD applications.

well you better explain to me why,..

[DmaxMaverick]

well you better explain to me why,..

The 5068 EEPROM REQUIRES the 5068 pump to operate properly. Any other EEPROM is perfectly happy with any other pump, including the 5068 pump. It's the EEPROM, not the pump, that's unique (except the relation of the pump). Why they did it? I don't know, but that's how it is. If you have a 5068 pump, it will work with any EEPROM. If you have a 5068 EEPROM, it will only work with a 5068 pump. You have a 5521 EEPROM, so you don't have to deal with any of that nonsense.

[phantom309]

The 5068 EEPROM REQUIRES the 5068 pump to operate properly. Any other EEPROM is perfectly happy with any other pump, including the 5068 pump. It's the EEPROM, not the pump, that's unique (except the relation of the pump). Why they did it? I don't know, but that's how it is. If you have a 5068 pump, it will work with any EEPROM. If you have a 5068 EEPROM, it will only work with a 5068 pump. You have a 5521 EEPROM, so you don't have to deal with any of that nonsense.

Thanks for the three peat but there's no facts here,..
Why won't a 5068 e prom run a 5521? What driveability problems arise? is there anywhere i can read about this? There are MANY posts stating it won't work regurgitated over and over again,... but no concrete facts that i can find,.
Can you post some links??

[Kennedy]

I've worked numerous customers through correcting this issue over the years, but most are long distance. I did have one here locally that was a 94 with the old 5068 eprom running a later model pump. It started and ran and the owners thought it was fine, but to me I could feel that just was not "right." It started harder than it should plus it had a little stutter-step when you went to accelerate. A nice puff of white smoke at times as I recall.

In simple terms it just was not as responsive as it should have been. I've encountered this so many times that I added a 5068 conversion chip option. This is a stock chip matched to the pump model. Whenever I do a performance chip I request the pump model number. I just need to know the pump and do not match to the Eprom as it may be wrong. Match the pump and all is well.