Jeep Enthusiast Forums banner

No Fire, Where Should I Begin?

1K views 21 replies 6 participants last post by  oldtime_ironman 
#1 ·
I have no fire on my 91 YJ 4.0. Where should I start???? Thanks.
 
#3 ·
no don't start there... start by doing a code scan...

turn the key from the off position to the on position 3 times... on the 3rd time leave it on, and your check engine light will start blinking... count the blinks and then look up the codes... for more information just doing a search on the forum... that's where you need to start to save money...

if you get code 11 which is a blink then a pause then another blink and a long pause.... you have a crankshaft position sensor going bad or a camshaft position sensor going bad
 
#6 ·
It's usually a bad crankshaft position sensor, or sometimes a bad coil. BUT look at what cevans said: get the codes from the computer first. It will save you some grief because the jeep computer is one of the best diagnostic tools all by itself!
So why not get the codes and then get back to us?
 
#7 ·
if the crankshaft position sensor is the one that bolts to the bell housing then i already replaced that last week... my fuel pump wasnt coming on so i thought that was the problem. i ran a power wire straight from my battery to my pump and it came on and ran fine. so theres no fire and the fuel pump isnt coming on without me forcing it on (holding the hot wire to it). but ur right, ill try the code thing when i get home and get back to you.
 
#8 ·
#12 ·
Yes, you can also check power to the ecu on pins 3 and 9 on the ecu connector with the key on. You should see 12 volts on both pins. If you have power on those 2 pins and no CEL then read the link I posted about the ecu.
 
#16 ·
ok good news, sorta...

because i didnt have the 470uf cap i just plugged the ecu back into my jeep and hooked my ignition coil back up. fuel pump came on, it cranked for a few and was wanting to run but wouldnt idle. when i gave it some gas while cranking it, it would run, but not idle with my foot off the pedal. after about 3 minutes, it finally started to idle. i let it run for about 10 minutes.

so where does that leave me? do you think theres still something that needs to be changed out? (either the caps or the ignition coil) or do you think maybe something was just loose and i snugged it back down when i hooked everything back up?
 
#17 ·
That is a standard ECU. If your CEL came on when you cycled the key then it wasn't the cap issue. I think you were just not getting the key cycle correct. Look at this and retry it:
 
#19 ·
checked the codes... i got a 12 and a 33.

33 = Air conditioning clutch relay circuit open or shorted ( Also will show up for rigs without AC)

12 = Memory Standby power lost (Batt or computer recently disconnected)

so basically it told me nothing. i dont have my a/c on it anymore and i disconnected the batt and ecu to check the caps on the ecu. so im pretty much lost now, ive done everything i can think up.

now it just doesnt idle by itself. i have to stay on the gas a little. after about a minute, i can let off the gas and it will idle and run just fine.
 
#20 ·
checked the codes... i got a 12 and a 33.

33 = Air conditioning clutch relay circuit open or shorted ( Also will show up for rigs without AC)

12 = Memory Standby power lost (Batt or computer recently disconnected)

so basically it told me nothing. i dont have my a/c on it anymore and i disconnected the batt and ecu to check the caps on the ecu. so im pretty much lost now, ive done everything i can think up.

now it just doesnt idle by itself. i have to stay on the gas a little. after about a minute, i can let off the gas and it will idle and run just fine.
Well, now you got spark. But since it doesn't idle I'm betting its a fuel issue.
 
#21 ·
It could be fuel, it could be tune up time. If it's changing cold to warm and you can get a good idle warm chances are one of the sensors are not giving the ecu what it needs. There is a sensor call the IAC that is responsible for idle along with the Throttle position sensor. I would start by cleaning the throttle body, IAC, and TPS and if it's been more than a few years give her a tune up with a new fuel filter, plugs, etc.
 
#22 ·
^^^ X2 what Que said. I always tell people to put a good tune up and check for codes first. So that way you know what you have, and a good base line to measure from. The tune makes a *huge* difference on these engines.

By the way, how the heck did you get the gunk off the top of the computer board?
 
This is an older thread, you may not receive a response, and could be reviving an old thread. Please consider creating a new thread.
Top