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1988 S15 2.8L V6 to 350 Engine Swap
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GMhead
Novice
Apr 5, 2009, 12:59 PM
Post #1 of 12
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1988 S15 2.8L V6 to 350 Engine Swap
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1988 S15 Jimmy, can't find RPM wire and temp sensor for gauge. Input would be appreciated. I have an 1988 S15 GMC Jimmy, It had a 2.8L V6 but I put a Chevy 350 in it with Electric fans and a MSD distributor which runs on a switched power lead and a RPM wire. I am trying to retain the stock gauges and I wanted to know (A) Which wiring harness off of the stock 2.8L distributor contains the "RPM wire" and which wire is it and (B) which sensor sends the temp signal to the temperature gauge, is it the temp sensor/sender in the cylinder head (runs on oil temp) or the temp sensor/sender in the intake manifold (runs on coolant temp)?
I am asking because I must retain the one that sends the temp signal to the temp gauge while replacing the other one with the new temp sensor that runs the electric fans.
Thanks a million!!!
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Tom Greenleaf
Ultimate Carjunky
/ Moderator
Apr 5, 2009, 7:03 PM
Post #2 of 12
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Re: 1988 S15 2.8L V6 to 350 Engine Swap
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I think temp guage sender is on side of 350s on head. For the temp switch for fans find a plug near thermosat that will trigger fans at the prescribed temp of the switch chosen. It's kinda see what works best for this special transplant which is done with some regularity to my surprise!
Gauge sender from the 2.8 may work directly on the 350.....
T
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DanD
Veteran
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Apr 6, 2009, 3:05 AM
Post #3 of 12
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Re: 1988 S15 2.8L V6 to 350 Engine Swap
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The “RPM” wire would be the white wire (terminal “A”) coming off of the original ignition coil’s wiring harness.
The temperature sensor for the PCM (computer) is the two wire connector with a yellow (signal return) and blue (ref voltage) wires. It’s located in the left front corner of the 2.8lt intake manifold.
The temperature switch for the temperature gauge is a single dark green wire; the sensor is located in the left front corner of the left cylinder head.
Both of these sensors, sense engine coolant temperature; I can’t ever remember GM using an oil temperature gauge; not back then, on a passenger vehicle anyway.
Dan.
Canadian "EH"
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GMhead
Novice
Apr 6, 2009, 12:03 PM
Post #4 of 12
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Re: 1988 S15 2.8L V6 to 350 Engine Swap
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Thanks a lot for the input guys, I will certainly put it to good use. I asked because the temp sensor/sender in the 350 head is a one wire and the the sensor from the 2.8L cylinder head is a 2 wire. I'm going to interchange the sensor from the 350 cylinder head with the sensor the that came with the fan relay kit which is also a one wire and just tape off the remaining 2.8L wiring because the relay kit is stand alone. I retained the sensor/sender that came out of the stock 2.8L intake manifold, which with the given information should control the temp gauge? I don't understand is why a truck that originally came with a clutch fan would have two temp sensors/senders. If I interpreted anything wrong please feel to correct me, once again thanks for the input!!!
To clarify, no, the truck doesn't have a oil temp gauge, that was my error. The sensor in the cylinder head must monitor the coolant temp or at the head.
(This post was edited by GMhead on Apr 6, 2009, 12:07 PM)
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Tom Greenleaf
Ultimate Carjunky
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Apr 6, 2009, 12:37 PM
Post #5 of 12
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Re: 1988 S15 2.8L V6 to 350 Engine Swap
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Re: Two temp senders.....
Even pre electric fanned the coolant temp switch was separate from the sensor for the light or gauge in many. The switches are for the electric fan and dunno where it would be placed. I might pick a spot for relevent need for a fan and make one up as personally I'd only want an electric fan to come on below the thermostat's rating based on temp of return coolant but who am I to decide??
T
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Loren Champlain Sr
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Apr 6, 2009, 4:16 PM
Post #6 of 12
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Re: 1988 S15 2.8L V6 to 350 Engine Swap
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GMhead; Didn't realize this was going on in two areas of the forum. The single wire sensor in the cylinder head is for the temperature guage ONLY. The two wire sensor in the intake manifold (usually by the thermostat) is for the computer. The computer needs this information for fuel delivery at different temps.
Loren
SW Washington
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GMhead
Novice
Apr 7, 2009, 2:05 PM
Post #7 of 12
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Re: 1988 S15 2.8L V6 to 350 Engine Swap
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Ok, as far as the "RPM" wire (white), i've found and matched that up... so that's good! As I understand the temp sensor in the intake manifold (2 wires, yellow and blue), which I've also matched up and the colors are correct, is for the computer for fuel delivery purposes so i'm going to leave that as is. And as for the temp switch in the cylinder head, i'll just try to use the existing one from the 2.8L because its 2 prong with 2 wires and the 350 temp switch is only a 1 wire and might not be compatible with the gauge IF I can get it to work.
But with all of this being done another problem has presented itself. As is so common with these kinds of engine swaps, since I'm leaving the existing temp sensor in the intake manifold for the (PCM), the intake manifold doesn't have anymore spots to put my new aftermarket (1 wire) temp sensor for the electric fans. So my question is: Is it ok to just put the fans on a switched (+) lead so they come on with the truck and stay on, or do I splice the "1 wire" that would've gone to the aftermarket temp sensor for the fans into the PCM temp sensor (Yellow or blue wire) and have it work that way? Or are there any other suggestions? I know Jeg's sells a temp sensor that slides into the upper radiator hose, would that be a good alternative?
Thanks again guys,
-GMHead
(This post was edited by GMhead on Apr 7, 2009, 2:23 PM)
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Loren Champlain Sr
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Apr 7, 2009, 3:50 PM
Post #8 of 12
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Re: 1988 S15 2.8L V6 to 350 Engine Swap
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Don't use the CTS connection going to the PCM. The temp sensor for the fan should be mounted in the cooling system....usually near the thermostat or in the radiator, itself. The one you mentioned from Jegs should work fine.
I'm still concerned about the 2.8 and 5.7 computer compatability. I may be wrong, but I think you have opened a bucket of worms when it comes time to try and run it. 
Loren
SW Washington
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GMhead
Novice
Apr 7, 2009, 5:14 PM
Post #9 of 12
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Re: 1988 S15 2.8L V6 to 350 Engine Swap
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Computer compatibility as far as the temp gauge, the PCM, or both? I sure hope not, this has already been a costly enough engine swap. Since I've gone from the electronic throttle body to carburetor, although I'm still using an electric fuel pump, do you think I'll still need to retain the temp sensor for the (PCM)?
(This post was edited by GMhead on Apr 7, 2009, 5:17 PM)
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Loren Champlain Sr
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Apr 7, 2009, 5:19 PM
Post #10 of 12
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Re: 1988 S15 2.8L V6 to 350 Engine Swap
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Oh, I forgot that you were going with a carb. No, the CTS shouldn't have anything to do with anything, and you could use that port for your cooling fan switch. Forgive me for being old and no longer having a memory, but what carb are you going to use? As long as it isn't a feedback, you should be okay.
Loren
SW Washington
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Loren Champlain Sr
Veteran
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Apr 7, 2009, 5:24 PM
Post #11 of 12
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Re: 1988 S15 2.8L V6 to 350 Engine Swap
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GMhead; What about emission testing in your state? Is the vehicle old enough that it is exempt? I think you can pretty much trash the computer system and go with the old stuff. (not that you have a choice) HEI distributor w/vacuum advance, electric choke, ect. If the engine runs well enough, it should pass tail pipe emissions anyway.
Loren
SW Washington
(This post was edited by Loren Champlain Sr on Apr 7, 2009, 5:25 PM)
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GMhead
Novice
Apr 8, 2009, 4:25 AM
Post #12 of 12
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Re: 1988 S15 2.8L V6 to 350 Engine Swap
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Oh, that's quite alright... I appreciate the help anyway I can get it. I'm Using a Holley 650 with vacuum secondaries and an electric choke with an MSD vacuum advance distributor. Luckily enough, Michigan doesn't have any emission testing so I'm all squared away in that area, no inspections necessary! Nevertheless this is great news... Problems solved!
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