reformedricky

Hello. First I'd like to say thank you to this community. I've learned a lot from the write ups and tips.

I've got a newly acquired 1990 Jeep Cherokee recently rebuilt 4.0 engine. The motor blew up shortly after I bought it :/

while the engine was getting rebuilt I went through Cruiser54's Renix Tips and found that the throttle body was opened way more than it should have been. I closed it and cleaned it, adjusted TPS per Cruisers tips.

I have a low idle <300 rpm here are some diagnostic hints i've found.

• when I first turn it over the idle goes >1k rpm after it get some heat to it, it creeps down to <300.
• Upgrading the braided ground cable seemed to prolong the drop (I think).
• creating vacuum leak seems to make it better.
• unplugging IAC shortly after start up freezes the idle drop and it stays good.

I've done lots of reading and lots of tests, but I don't know what my next step is. here are some results of my sensors etc.

• MAP Wire B off: 4.11 volts; Wire B running: 1.8; Wire C: 5.0 volts
• CTS 344 ohms (180* (running cold stupid after market thermostat))
• IAT 750 ohms between 100 - 155*???
• TPS (flat connector) Wire A & B: 4.88 volts; Wire B&C .81 (17%)
• O2 Sensor A&B 27.7 ohms (???)/14.33 Volts (???) B&C 5 volts when off and seems to be rapidly jumping when on.
• EGR: engine dies when depressed; when revved, i can see the pin moving in and out.
• CPS: seems weak only .3 Volts AC when cranking. (will this show low idle?)
• I changed the injectors to 746's because one of my old ones broke upon installing... I need to check the fuel rail pressure. I don't remember if the idle was low before it blew up, but I don't think so however, this could have been because of the throttle body being partially open.

note: I found that if you use the formula -0.1962x+248.3 where x = the CTS in ohms, you'll get the temperature reading... this I guess this is only linear after 160* or so.


Cruisers tips completed:

1-Ground refreshing
3-Connector and relay/receptacle refreshing
4-Coil/ICM contacts
5-Checking sensor grounds
6-Sensor ground upgrade
8-TPS testing and adjusting
11-Throttle body and IAC cleaning
13-Renix Distributor indexing
14-Restoring throttle butterfly adjustment
21- Renix EGR valve test
25-Valve cover mod

reformedricky

Bueller?

LaredoBucket

I though Renix were 89 and earlier??

reformedricky

87-90

adamj

Seems like you've done a lot of investigating already, I subscribed to see what you come up with as far as a solution/remedy. How about fuel pressure regulator? Would that be something to check out?
Hope you get this figured out.
Just wondering, do you have a steady idle? Or does it waver/hover a bit (up/down a few rpms)

reformedricky

Yeah, vatozone didn't have a tester I could use. That would have ruled out the regulator.
My idle is steady when it first starts but when it drops it fluctuates 50 rpm or so.

Cheddarnut

Not sure if you have harbor freight nearby...twenty bucks.

http://t.harborfreight.com/fuel-inje...18%2Findex4%2F

cruiser54

How's the line from MAP to throttle body?

Great job so far BTW.

reformedricky

Thanks! I changed the hose when the engine was out because it cracked a lot. Not sure if the ID is the same. I'm also not sure what that hole is above where the map hose goes in on the TB

cruiser54

Make sure it's not leaking.

reformedricky

Doesn't seem to be (sprayed TB cleaner) but I noticed the top piece came off of the rubber (wherever it does) gonna try and seal the bottom to make sure.

cruiser54

Hose goes into the vacuum hole in the bottom. That "plug" goes into the top hole to secure the assembly.

reformedricky

update: I sealed the MAP lines with RTV, used a zip tie on the connection to the nipple. However, this did not work. the problem still exists.

things i've noticed: if I unplug a vacuum line the idle gets better (not A LOT better) after i unplug it, the IAC takes over and makes it worse again... if I plug the hose in again, the jeep just about dies... but then the IAC seems to open up and keep it alive.

I removed my CPS and drilled a bigger hole and cleaned off the tip... now my reading is 1.02 vAC!!!!! more than double what it is supposed to be? don't think it's related.. just crazy...

don't know what to try next.... would exhaust restriction cause this? do i need to clean my TB more?

cruiser54

What size did you drill the CPS? The upper hole only, or both?
Throttle body needs to be spotless including the edges of the blade.

Which vacuum line do you unplug?

reformedricky

I drilled a 3/8" hole on each side of the CPS was i just supposed to drill one?
I think I left some grime on the sides by the connecting rod of the butterfly valve. i'll clean that up. I also noticed that the blade catches on something if i open it slightly.

I unplugged the line on the manifold that goes to the firewall side of the valve cover.