Motorhome Carb to EFI Conversion

[mh86]

Hello to everyone !! I'm trying to gather helpful information for my project which is: Installing a 1993 C3500 454 complete engine and wiring harness into my 1986 Holiday Rambler motorhome. I am kind of new with forums and the first thing I'll try and figure out is what a message "tag" is !!! Happy thanksgiving to all !!!

[dave w]

Would it be possible to get the 454 TBI engine running on an engine stand before you install it? The engine pictured is a 1998 Vortec 454.

dave w

[mh86]

After viewing info on ecm s/n 1228747 that I removed from my 1993 C3500 454 std 5pd I was suprised to find in the GM
ECM Forum it shows that ecm was used in 89-90 Chevy trucks. I'm not sure why that is or if it will make any
difference in the engine and carb to tbi swap. I just bought the '93 3500 recently just for the purpose of using the
gen5 engine with tbi in the '86 motorhome P30/markIV/454/carb/th400. I don't have an engine test stand but did do
some scanner and fuel pressure tests before starting engine removal from the '93. I replaced a defective temp sensor
and single wire o2 sensor but never able to get into closed loop. I began removing the engine from the '93 today and
did notice some extra wiring that looked like 2/wire o2 sensor connectors. So it's possible previous owners made
changes to who knows what! So in light of all that my plan for tommorow is finish removing the engine from the '93
and turn to the '86 to make sure the in tank fuel pump will supply enough pressure and volume to supply the TBI which
is about 30' from the 60 gal fuel tank. Any advice would be appreciated.

[1project2many]

Welcome.

I was asked to get involved in a similar project years ago but the owner of the motorhome decided the cost to do the job the way I proposed was too high. He tried to do it himself but ended up selling the vehicle in a state of partial completion when he finally realized it was no small task. It was too bad that he didn't give me the job. It would have made a nice swap project.

The ecm will likely work although there may be some mild tuning changes required to the calibration. If you're using a Turbo 400 then you should get a calibration for an automatic trans. Some of the one ton truck calibrations wouldn't enter closed loop at idle. A few wouldn't enter closed loop at all. Is there a three or four letter code on the chip? The distance between tank and pump shouldn't present a problem, but the type of pump will. Is the in tank pump configuration original to the motorhome? Carburetors typically run with 5-7 psi pressure and the TBI system will definitely need more pressure than that. As far as the connectors, harnesses are often built with extra connectors. If you want help ID'ing the connectors try to get pictures and wire colors and post them here.

[mh86]

I have the '93 engine ready to pull tomorrow morning. I pulled the ecm but cannot view the numbers on the prom because of the enclosure on the chip and didn't want to damage it. I did get the ID #6561 from the scanner. Is that number sufficient to identifiy the vehicle and equipment in the vehicle such as auto or standard trans? When you mention tuning changes to the calibration, what all is involved in doing something like that and what type changes can be made?

It seems the '86 was equipped with a high pressure (not sure how high yet) in tank pump and then an inline regulator to step down pressure to the engine carb and an additional line and regulator stemming off to the Onan generator carb which can only stand 2.5#. I submitted a few pics to give a general idea of where I'm at. I will post more details as I progress.

With regards to the overall wiring in this project I have it in my head that I could add an auxillary fuse panel just for the purpose of operating the ecm and engine controls in concert with the existing wiring and fuse panel in the '86. After I pull the underhood wiring from the '93 and lay it out in the shop I'll be able to get a better picture. In the mean time I'm definitely open to any and all suggestions and senerios. thanks

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I'll try to figure out how to make bigger pictures next time!!!

[1project2many]

You can leave the pictures like that. The forum software automagically makes them smaller. If you click on one it opens a new window to view the full size picture.

Tuning involves new tools and skills... electronic components to read, erase, and program chips, new programming software, additional software to interpret what's on the chip, and even more hardware and software to monitor how the engine is running. It might be helpful to obtain the tools and learn the skills but for a single project with mild changes you might just want to contact someone who can make the changes for you.

The only file I can see in the online lookup with that scan ID is from calibration ABFK, a 305 with auto transmission, 1988 model year, and 1227747. Either someone jammed a chip into a computer and a computer into the truck, or the scan ID isn't listed and we'd need to get the actual code from the chip.

Please, please consider safety first. I've seen to many motorhome fires caused in part by mechanics (pro and amateur alike) who do not understand how hot these vehicles can get and how hard they work. Take time to lay out the plumbing. Keep the fuel lines as far from exhaust as possible. Watch battery and power cable routing and use plenty of circuit protection. I am not making a comment on your ability, just putting the request out there.

Do you have a factory service manual and / or wiring diagram for the '93 truck? A subscription to AlldataDIY for this vehicle might be a good investment.

An auxilliary fuse panel should work. Find a dry and secure place to mount the ecm. That controller was designed to be inside the cab where extreme heat and rain would not affect it. Your fuel system will need a return line as well as the pressure line so you may be running a second line to the engine?

Good luck and keep us updated!

[mh86]

Engine pulled out of the '93 yesterday. Ate turkey today and started filling my head with ecm stuff. I finally got brave enough to remove the 24 pin chip from it's holder and was able to barely read the ID #which is 8197 and not the #6561 that I gave on my last post. So the correct numbers and letters are 1228747, ARPA, and ID 8197. I found reference to 1228747 that applies to 87-92 C/K trucks with 5.7 and 7.4L (HD) which the '93 is, but can't find any reference to the ARPA or 8197. I hope that info is helpful.

I did look a bit into the fuel plumbing and was able to adjust the regulator as high as 19 psi and ended up setting it to 13 static and flowing at a steady 11. I thought that would be a good starting point. The Mitchell book said 9-13. The pressure line is 1/2" metal line running front to rear and the return line is 5/16" also metal aside from connections at both ends. Unfortunately they are on the passenger side frame rail up to the old fuel pump position. I'm going to try to use metal line from that point over to the other side to an inline filter and possibly into the original lines pulled from the '93. I will make sure I use fuel injection hose for any connections.
When I pressured up the intank fuel pump the line pressure drops off completely within a few seconds without any apparent leaks. Do some type intank pumps bleed off and others don't and could that be an issue ?? I don't recall that happening whenever I checked other efi systems.

It's 2am, so here are a few pics. thanks


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