No Start?

Ok, I am just finishing up a motor swap on my 1989 Cherokee. I swapped in (from a running 1995 Cherokee parts vehicle with a 4.0L/ AW4/ NP231) the motor, trans, t case, and wiring harness.

It is not starting, I believe that it is fuel pump related (I'm still using the fuel pump from the 89, if that matters). I believe its the fuel pump because, when i turn the key on, the fuel gauge reads 1/2 tank. But as soon as i try to crank it over, the gauge drops down to empty. Also, it doesn't seem like there is any fuel pressure at the rail.This leads me to believe that, when i start to crank the engine over, I am loosing power to the fuel pump. Is that a correct assumption? I plan on checking the voltage at the pump this weekend when i have someone to help me out to figure out if i am actually loosing power at the pump.

Is there any where else i should be looking instead? Thanks in advance for the help:smootch:

Why does it seem like no fuel pressure? Did you check to see if fuel sprays out of the Shrader valve or test the pressure at the valve with a gage? Or try starting with spray start? Or pull a spark plug to see if it's dry? Or try the opposite approach and check for spark. Usually it's spark or fuel. Did you change the PCM with the wire harness?

The PCM went in with the wiring harness. I basically have a 1995 Cherokee on an 89 body/frame . I never thought to try the shrader valve at all, I just squeezed the fuel hose to see if I could make it compress. i don't know if there is enough pressure in the line to make this a reliable test, but it was just a quick idea i had before i had to go. Tomorrow ill test for spark. Is it normal for the fuel gauge to drop to empty when you try to start it? I have never seen that before, and thats kind of what is making me think its some kind of electrical issue related to the fuel pump.

I don't think the pump would affect the gage. Unless it was a bad ground.

Checked wiring (at least on a 2000). It is not a common ground. The pump grounds to the body and the gage grounds through the PCM. Is the battery strong enough?

If the entire fuel injection harness and computer went in with the engine, only that part is OBD1. The rest is still Renix wiring - including how the computer interfaces with the fuel pump, etc.

A sit down with both wiring schematics, and a pot of coffee, will alllow you to trace out the diagrams side by side and determine exactly what it different. Cherokees went through major wire harness redesigns on a periodic basis. The 87-90 is different from the 91-96 and may have imtermediate changes. Obviously, Renix and OBD1 don't substitute well, but there is no guarantee the body harnesses are compatible.

Good Luck.

most of the guys I know just keep the Renix fuel injection system and put the HO engine in with it - it runs really good and is alot less hassle than what you're trying to do - not to say its impossible or a bad idea its just tougher

noooo, the ENTIRE wiring harness came out of the 95 and went into the 89, including the interior harness and fuel injection harness:doh:. The only thing that is still 1989 on it is the fuel pump and the body/frame. so it is not because of the harnesses not interfacing with each other, but maybe the fuel pumps are different. I did test for spark today, and it has it. So the next time i get a chance ill check for fuel pressure. Thanks for the help guys

I might have an idea on the fuel gauge.

Renix period sender is low ohm = empty, high ohm = full.

Then there was a change that reversed that. Anybody on here remember when that was? Did you change the fuel pump and sender?

so there is a difference between the renix pump and the 95 pump! Well i guess the next thing i'm doing is putting the fuel pump in from the 95 and see what happens.

I do not know about the pump, I was referring to the fuel gauge sending unit, and again I don't know what year the change was in.

Found another thread. When changing to the 1991+ the fuel gauge sending unit resistance is opposite of the 1990 and earlier. So, If you used the harness for the 95, did you change the instrument cluster too? If you did, then the 89 sending unit is backasswards for the 95 harness/cluster.

I did use the new instrument cluster in the swap. I did figure out the problem though, there was a short between the fuel pump relay and the fuel pump, which caused my gauge to malfunction when the pump got power. So i eliminated the short, and it started :cheers: thanks for the help guys!!! Oh, is it just me or is the pump loud? i never remember it being as loud as it is now. is there supposed to be a ballast resister in the 95?