I have a 1987 Jeep Cherokee with the 4.0 - 6 and automatic
I have recently incountered a problem starting the engine when its been setting for a 1/2 hour or more.

The engine strart when primed so it is a fuel delivery issue. (injectors not fireing)
I have changed or checked the following:
New items:

Fuel pump
Fuel filter
Fuel pump relay
Crank Sensor
TPS
Cam Sensor (Pulse generator)
Start relay
I have checked:
MAP sensor
Oxygen sensor (heater side only)
Oxygen sensor relay
Maniford air temp sender
Coolent temperature sender

The items that were checked were found to be within specs per the Renix manual

I am lost and definately need help. I suspect the issue is with the ECM but the car runs fine after started. Any suggestions?

 

I'm also having fuel pump/starting issues and I've narrowed it down to the ECU. It's a worthwhile bet for you as well

 

Renix 4.0s seem to have a mind of their own. I had a '87 with a similar problem. Never figured it out since it ran so well every other time other than the hard start after sitting like you explain. I havent had a lick of trouble with our '89 renix powered XJ though.

 

several other factors to consider:

1987 has an extra connector between the motor and engine bay harness. it typically corrodes. it is called a C101 connector


there was a recall, in which they bypassed the C101 for the crankshaft position sensor wiring directly through the firewall, to the ECU above the gas pedal.

I've had that cause similar issues, especially when it's humid out. bypassed, fixed.

another thing, bypass the ballast resistor (white ceramic located on the driver's side of the engine bay...two wires going to it) by making a jumper wire. this is a basically pointless resistor that more or less acts as a sound deadener for the fuel pump. they can partially fail, and when there is no current running through them, the resistor spring contracts...i.e. cool down after shutting down engine, and it takes quite some time to get it warmed up enough to get the two broken halves of the spring to make contact. you can replace it for under $10, and use a jumper wire to make it run.

the likely-hood of the ECU failing is fairly slim. chances are it's bad/dirty connections, or a bad resistor.

 

the other thing that I would do is check your injectors... or upgrade to the 703's it fixed a friend of mines similar problem...

 

Welcome to CF.
I don't know very much about the Renix system, but here's something that might help. http://www.lunghd.com/Tech_Articles/...iagnostics.htm
There's a pic of the ballast resistor for the fuel pump there w/the EGR info.

 

another thing, bypass the ballast resistor (white ceramic located on the driver's side of the engine bay...two wires going to it) by making a jumper wire. this is a basically pointless resistor that more or less acts as a sound deadener for the fuel pump. they can partially fail, and when there is no current running through them, the resistor spring contracts...i.e. cool down after shutting down engine, and it takes quite some time to get it warmed up enough to get the two broken halves of the spring to make contact. you can replace it for under $10, and use a jumper wire to make it run.


Sorry to get off topic but in order to jump the ceramic ballist resistor I just connect the two wires that connect to it together??? Mine wont let my truck start sometimes, mostly do to corrosion. It seems to corrode quickly even after I clean it.

 

yep. you have to make a jumper wire for it that has two male spade connectors on it so it can plug in