a rough start thread...again

I have searched and searched.... Researched and put in parts...

Jeep:99 cherokee i6, 157,xxx miles, AW4

new parts in last 6-8 months:
Water pump/radiator and hoses
Fuel pump
TPS
IAC
O2 sensor
ignition wires
cap and rotor

New parts this week:
Precision fuel injectors
5-90 4 awg battery cables
Big offroad head light kit
Crankshaft pos. sensor
plugs
Ignition module

2 weeks ago
When it got down to 0 degrees here in Denver i went to start my jeep (it sits for a week or two cause it is not my DD) and it had a slow crank and would not fire. Thought it was the battery so switched batteries with my friend with no avail. After letting it sit and randomly starting it with gas pedal to the floor it slowly came to life. I narrowed it down to having to heavy of weight oil in there so i changed it to 5-30w.


Fast forward to the next weekend i get my battery cables and injectors. I go to start it to get it in the garage and it just cranks and cranks then slowly comes to life w/a rough idle (bout 40 degrees out).Let it warm up to operating temp. Change out the battery cables and it comes to life instantly seriously one crank.

Next day install the injectors. Had a problem with the #1 injectors o-ring leaking, replace that and it is sealed. Then got a CEL for the #1 inector not getting a good connection (PO201) giving it a rough idle. fixed that and it ran great!

This weekend i install a big offroad light harness upgrade. went to start it up (40-50 degrees out) and it still cranks and barely starts up. so i replace spark plugs, ignition module, and Crankshaft pos. sensor. Runs like a champ but it again even after being in a warm garage did the Crank...crank.... slow start then rough idle.

The long cranks aren't always happening i can start it one time and it fires right up and sometimes it just cranks. The cranks are fast too not like a old/bad starter (except the 0 degree start up, that was slow). the idle is fine after a few seconds.
It doesn't seem to be weather or rather temperature sensitive it just happens. I checked all the battery grounds and used di-electric grease every where. My battery is good and still holds a charge.
haven't put a gauge on my fuel rail yet but when i pushed on the valve after the jeep had been sitting for a while (3-4 hours) there was still alot of fuel in the rail. making me believe it is not a leaky injector, but not positive.

Any insight would be much appreciated.

Always start with the battery. If you don't, you can just end up P/ing into the wind.

Pull the battery and put it on a charger for 24 hours, then let it sit outside overnight before taking it in for a load test.

Starter-solenoids are volts stupid and amps happy. That means you can get a pretty good cranking out of it while the voltage may drop below 9.0 volts and result in the engine management system, which is volts happy and amps stupid, to act up or fail completely.

Post up your results.

And along with LOAD TESTING of the battery, (free most anywhere) I would recommend that you actually "freshen" your engine grounds. Disassemble, clean, reconnect. Sometimes a simple test of them isn't enough. Grounds deteriorate over time...........

If after that, you are still experiencing an extended crank, I would try the "poor mans prime" as a quick and dirty test to see if you have a serious fuel pressure drop.

1. Turn the key to the ON position (don't crank the engine). Fuel pump will energize and run for about 2 seconds.
2. Turn the key to the OFF position
3. Repeat the above two steps TWICE more
4. NOW crank the engine over.

If it starts quickly and cleanly using the poor mans prime, then you have identified a pressure drop situation and you would need further testing with a gauge/adapter/clamp, to identify exactly where you are losing your mojo.

joe_peters said:

Always start with the battery. If you don't, you can just end up P/ing into the wind.

Pull the battery and put it on a charger for 24 hours, then let it sit outside overnight before taking it in for a load test.

Starter-solenoids are volts stupid and amps happy. That means you can get a pretty good cranking out of it while the voltage may drop below 9.0 volts and result in the engine management system, which is volts happy and amps stupid, to act up or fail completely.

Post up your results.

Click to expand...

i have a trickle charger on my optima every day (its a solar charger), and even if the battery was dead switching out to a "known" good one with my friend would of shown that it was the problem.

I am starting to suspect it is the starter as i watch my amp draw on the guage cluster and it drops alot when cranking down to about 10 amps.

birchlakeXJ said:

And along with LOAD TESTING of the battery, (free most anywhere) I would recommend that you actually "freshen" your engine grounds. Disassemble, clean, reconnect. Sometimes a simple test of them isn't enough. Grounds deteriorate over time...........

If after that, you are still experiencing an extended crank, I would try the "poor mans prime" as a quick and dirty test to see if you have a serious fuel pressure drop.

1. Turn the key to the ON position (don't crank the engine). Fuel pump will energize and run for about 2 seconds.
2. Turn the key to the OFF position
3. Repeat the above two steps TWICE more
4. NOW crank the engine over.

If it starts quickly and cleanly using the poor mans prime, then you have identified a pressure drop situation and you would need further testing with a gauge/adapter/clamp, to identify exactly where you are losing your mojo.

Click to expand...

The grounds are all clean as i grinded, sanded, and put di-electric grease on all of them when i installed my new battery cables. Though this problem popped up before the battery cables, and the cleaning and replacement did not make a difference.

the prime is fine, like i said it is a new fuel pump and when it has been hard to start that is the first thing i do is cycle the key a few times and listen for the prime. I hear the prime and it always sounds strong.

Just attempted to start the jeep after sitting since last night.....Crank CRANK crank, it sounds like it wants to kick over but it just can't light up the cylinders. tried several times but did not want to push my luck on the battery dying.

I am going crazy here. Before 2 weeks ago it was starting strong every time.

Re: a rough start thread NOW NO START...again

mistake didn't mean too post

fuses are good, wiggled the shifter, started in neutral, checked the grounds, especially around the starter, pulled and switched around the relays, and pulled and cleaned that MAP sensor connection..... nothing worked

Bout to pull the dizzy cap and pull the Camshaft positioning sensor, check that, see if there is anything obvious in there.

Not the Camshaft positioning sensor.
Tried putting a Brand new battery on it, nothing changed. Crank sounded the same and no fire.
pulled the plug and still have spark. Though after a few times of trying to start it then pulling the plug there was some fuel on the plug. Don't know if thats bad or just cause it didn't fire.

Coolant temp sensor..... Sounds like your flooding.

Cleaned the connections to the computer it sounded like it was a stronger spark/sputter but still no fire.


Thank you for the input i will start looking down that road. though now that CTS, MAP sensor, and ECU are the only things i haven't replaced.
My cousin is coming over Friday to bring over a fuel gauge. See if everything in my fuel is tip top, though i don't see any way it is not but i need to double, triple check everything.

the fuel pump has a valve to prevent total drain back.did you replace just the pump or the whole assy in the tank.the fuel system is one of the few the computer does not moniter

So does it start easier after you "prime" it?

I would really check that ECT coolant temp sensor.

I had the same problem and after I checked everything, it was the ECT.

91to99 said:

Coolant temp sensor..... Sounds like your flooding.

Click to expand...

Now that you've eliminated the battery, i'll second the Coolant Temp Sensor. Sounds like it may be telling the computer a lie about what the temperature really is, and thus throwing off the proper mixture needed to fire.

Mine used to go through a similar hissy fit, mainly during drastic temperature/humidity changes..much like you're seeing. I would have the most problems in Spring and in Fall. Eventually, my CTS failed all together one day this driving down the highway and the gauge dropped to zero. Didn't notice the hard starting this past fall with having that a new sensor in place.

Cheap sensor...approx $20 if memory serves. So you're not out much if it doesn't solve the problem.

Air intake manifold temp sensor will do it too.

bought a brand new starter. not starting
Brand new Coolant temp sensor. not starting
Pulled and switched around 40 amp fuses. not starting

Skreed said:

So does it start easier after you "prime" it?

I would really check that ECT coolant temp sensor.

I had the same problem and after I checked everything, it was the ECT.

Click to expand...

It hasnt been starting at all.
Even when it was the "poor mans prime" never made a difference.
I am getting fuel. I will know my exact pressure tomorrow. but i know there is fuel in the rail and getting to the spark plugs.

1 tuff mj said:

the fuel pump has a valve to prevent total drain back.did you replace just the pump or the whole assy in the tank.the fuel system is one of the few the computer does not moniter

Click to expand...

I replaced the whole assembly in the tank filters regulator pump. everything. bought it at napa

Ecomike said:

Air intake manifold temp sensor will do it too.

Click to expand...

Just cleaned the Air temp sensor but it didn't seem that bad to begin with. I tried starting it up but no dice. still did the same thing. crank but no fire

Only thing left would be ECU and the MAP. My buddy is coming over tonight (i think) to exchange MAP sensors with me. See if i can get it to fire with his installed.

I have got a replacement computer lined up, if it comes down to that. .

Any current codes?
Your sure you have good spark from the coil? and to all the plugs?
Plz make sure you dont have any wires mixed up on the dist.