89 Comanche won't start without starter fluid

[atanaciop]

Hey Guys!  I've been reading this forum for about a week now, and tried a lot of different tips.  I recently picked up a 1989 Manual 4.0l Comanche and it's my first introduction to the renix system.  When I purchased it, it wanted to start but it just started and died with starting fluid.  Towed it home and went through all the Ground Refreshing tips, added fresh fuel (it had been sitting for a year), added new fuel filter.  Fuel Pump had recently been replaced.  Have proper fuel pressure at the rail 31-33 psi while running and around 39-40 psi when vacuum is pulled off the regulator.  Brand new NGK Copper plugs with factory .35 gap.  Anyway, it will not start when cold without starting fluid, it will just crank and crank and crank.  But one or 2 squirts of fluid and it gets going.  Idles great, and drives great after that.  Once the engine is warmed up I can start the jeep everytime after, but when cold it won't start at all.  I measured the CPS VAC and it was within range if not more 1-1.1v (not sure if that's to high?), and ohms were at 215.  I have noticed when I shift gears at around 3000rpm the exhaust backfires once.  I can reproduce almost everytime around 2500rpm-3000rpm.  I'm wondering if this could be a clue to why I can't start it.  Anyway any recommendations of where to look would be helpful thanks!  I included a pic of my new baby.

[87MJTIM]

Welcome to the addiction.

 

In order for you to help diagnose the Renix engine you should get two things: 1) The Renix engine control manual, and 2) Nickintime's REM module.

 

Both of these will help you.

[fiatslug87]

Welcome, add you VIN to the registry and someone will get you the build sheet https://comancheclub.com/forum/28-comanche-registry/

 

In addition to the RENIX fuel injection manual, the manuals here are very helpful https://comancheclub.com/topic/48710-diy-projects-writeups-master-search-index/

 

[JMO413]

Do you have fuel pressure when cranking?

[OldManComanche]

When the engine is cold, turn the ignition switch on (Don't crank the engine), do you hear the fuel pump come on for a few seconds?

[atanaciop]

Thanks for all the links @87MJTIM and @fiatslug87 will definitely bookmark those and go through everything.  Yes fuel pressure is at around 40psi when cranking @JMO413, and I can hear the pump running @OldManComanche  I actually bypassed the resistor so I could hear it.  and I can hear it loud and strong.  I primed the rail on/off/on/off/on and still nothing.  But this morning I took some of the gas from the tank and put a spoonful in the throttlebody, and it started right up first try.   So I feel like injectors aren't spraying during cranking, but as soon as the Starter fluid or gas in the throttle body ignites, then they start spraying and they continue to run.  Like I said once started she idles perfectly and revving is great.  The injectors are the Bosch type from @cruiser54's recommendations.  Is there something that might tell the injectors to spray during startup but no during operation?  I had taken the injectors out and tested them with a 9v battery.  they all click open and closed and carb cleaner can spray right through them.  It seems to me like it's a slight electrical problem.  since it starts and stays running with gas or starting fluid initially.  Then whatever residual gas is left in the rail or injectors is enough to get it going again when warm?  Thanks for any help in advance!

 

[JMO413]

This is from the 4.0 fuel injection manual.

[OldManComanche]

In the 4.0 fuel injection manual JMO413 posted, look at the second note. ECU thinks WOT and is not spraying fuel. A little help from some extra fuel in the intake will get it to crank 400 rpms, and start spraying fuel. when the engine is warm it will make it to the 400 rpm with out any extra help.???

[atanaciop]

I just saw this note, and thought the exact same thing!  I wonder what would cause the ECU to think it was WOT.  Sounds like that is exactly what is happening.  What could cause False WOT condition?  I'd imagine something with the throttle body, could a faulty TPS cause somehting like that?  

[atanaciop]

the previous owner gave me all the old parts he had changed out, and i found a brand new TPS in the bunch.  Wonder if that's something he never got to.  I had checked voltage on the TPS I have installed now and everything seemed to check out.

[Andy in Pa]

2 minutes ago, atanaciop said:

the previous owner gave me all the old parts he had changed out, and i found a brand new TPS in the bunch.  Wonder if that's something he never got to.  I had checked voltage on the TPS I have installed now and everything seemed to check out.

You may want to check the actual performance of the TPS with a meter.  Hook up a meter and move the TB open/closed smoothly and slowly to see if the TPS has any deadspots.  I can't help you on how to hook up the meter though, someone else will have to provide that info.

 

[atanaciop]

Also thinking maybe my starter is tired and not reaching 300rpm possibly....I'll check the tps tomorrow and try to track some of this down.

[atanaciop]

after a month of scratching my head cleaning bits and pieces, and trying multiple ways to get this jeep to start without starting fluid, I finally got it starting properly.  There were only 2 things that I did differently the other day that got it going.  I noticed my battery had stopped charging and the jeep would shut off when I disconnected the battery, so that told me my alternator was not working properly.  Replaced it with a new bosch unit and it still wouldn't start right up (I didn't expect that to fix the no start) but I started it up with starter fluid and let it run a while to charge the battery.   I noted all the sensors in crank mode and I hadn't really inspected the CTS, I didn't think that would cause a no start though so I just kind of ignored it.  After thinking about it I figured I'd take a look at it.  The previous owner had installed an after market coolant gauge and had tapped into the coolant temp wires to send it to the gauge.  I decided I just wanted to remove the gauge entirely for no reason, and unplugged all the connectors.  Decided to try to start up the vehicle, not thinking anything would change, and it started right up with no starter fluid.....I thought that was odd so I let it cool down and figured I'd try again a few hours later.  Tried it again once the engine was cool and it started right up again.....still thought that was odd that it started, so I decided to let it sit overnight and figured i would not start in the morning.  Tried it again the next morning and fired right up.  I've now started it about 10 times the past few days and have not had to use starting fluid......So my guess is that that gauge or tapping into those wires caused a weak CTS signal to the ECU causing a no start for some reason.  What a strange problem.  but Thanks so much everyone for helping me out!  Now I'll start working on all the small things I want to do with this truck.