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I own a 1995 Jeep Wrangler YJ 4.0L just got it reassembled after repainting I'm having 1 issue it's starting hard I replaced the iac valve no change when it starts firing it only sounds like a few cylinders until it warms up i have to keep my foot on the throttle slightly it sometimes back fires but once it's warm it runs perfectly fine. I don't have a vapor canister in it cause it got lost could that be my issue? 

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Hi, jjuststice85...Random possibilities would be the temperature sensor or the O2 sensor.  I would retrieve any codes stored and look for a MIL "Check Lamp" signal.  Is there a check engine (MIL) indicated?  You should get a code for common devices that have faults.

You do need a vapor canister to complete the vacuum circuit, and also to get proper pressure and seal at the fuel supply side.  If the misfire is from fuel starvation, this could be part of the issue.  Fuel pressure can be checked at the fuel rail.  (You have a two-rail EFI system.)  Logically, if the problem did not exist before the canister disappeared, this could be the source of trouble.  A vacuum leak could drop the signal to the fuel pressure regulator.  Low vacuum at the pressure regulator increases fuel pressure during cranking the engine over.  Once the engine produces vacuum, the regulator drops fuel pressure slightly.

Most issues that cause a problem here should throw a code.  Your Jeep is OBD-I still, you can benefit from an OBD-I scan tool to get codes.  Disconnecting the battery will clear codes.  You want the stored codes, so don't disconnect the battery before the initial diagnostic read.  (OBD-II like the 1997-up Wrangler is easier to diagnose, a $20 OBD-II reader from Harbor Freight can retrieve the codes quickly.)  There is the 3-turn ignition switch method for retrieving codes, though you need to pay attention for an accurate read.

I'm not a "parts replacer" unless there is a clear problem.  All devices can be tested for ohms resistance or voltage if necessary.  Some issues are fuel related, others vacuum or the PCM.  The crank position sensor, the throttle position sensor (TPS), a PCM plug contact issue or other message carrying devices can be involved.  

Did you unplug the PCM during work on the body?  Have connectors in the EFI sensor circuit been unplugged?  Sensor wires could now be making poor contact in the cold start or warm up circuit.  Grounds can always be an issue.  Did you paint surfaces where the body grounds attach?  If so, direct contact with sheet metal must be reestablished.  This is a D.C. system, grounds are as important as the positive leads.

Let's work through this...

Moses 

Edited by Moses Ludel

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The check engine light does work but isn't throwing a code but I have a guy with a snap on scanner going to hook up and see what he can fine. I double checked all my ground points and made sure they had a clean surface. I did have the pcm unhooked and only disconnected things needed to remove body from frame. Thank you Moses for the input it gives me a few ideas to start at. I'll double plug connection is there a spray or cleaner you recommend for electrical 

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I use Mopar Electrical Contact Cleaner in spray, though surely this is a private label product...A quality electrical contact cleaner will work, CRC is popular.  

Don't scrap the contacts with a sharp or pointed metal tool or knife, let the cleaner do its job.  Look for black oxidation on contacts, that's the biggest threat with electronics on automotive applications.  Scotch Brite fine grade pad will supplement the contact cleaner if necessary, avoid clawing at the contacts, use a brushing approach.

You're being methodical with the scan tool, there's a wealth of stuff that can be done with the right software.  Let's evaluate the findings...

Moses 

 

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Well got it checked out only thing electrical that failed was cyl. 1 injector  I got a set of 6 coming. Now on to the weird when I first posted my question it was mid 30's outside when I was having issues getting the jeep to start. On Wednesday it was high 50's and it fired right up no problem. The other thing that slipped my mind is why is the fuel pump and starter or it may be the ASD istead of the starter relay clicking really fast for about a minute when I prime the pump. Only does it if it's colder outside 

Edited by jjuststice85

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jjuststice85...I'm still suspect of grounds.  Resistance changes, including ground resistance, are affected by temperature.  Sensors like the temperature sensor (CTS) and crank position sensor (CPS), or ohms resistance at the relays, can change with temperature.  Fuel pump load can raise resistance, and this often is affected by cold weather.  

Poor grounds can increase resistance, sometimes causing issues in colder weather...See if the body to frame/engine ground has a paint barrier or limited contact.  Check the PCM ground.  Definitely check the frame to fuel tank ground, as too much resistance on this circuit would cause the relay to act up.  The fuel pump circuit needs proper grounding as much as it needs power.  Also make sure the power distribution box is adequately grounded.  This can affect relay performance.   

I'm curious how the injector change works out.  If the Jeep has higher mileage, the injectors might need attention.  There is also a "syndrome", however, of a #1 injector fault code that often turns out to be other issues.  If the new (rebuilt?) injectors do not remedy the troubles, we can discuss this further.

Moses

Edited by Moses Ludel

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The injectors are changed still having issues with a cold start and it has a miss fire when I'm on the throttle my buddy swapped me crank sensors for the fun of it mine worked just fine in his wrangler and there was no change in mine the relays are no longer clicking guessing a bad connection 

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jjuststice85...Relay not clicking now could have been a bad connection or poor ground...too much resistance in any case.

OBD-II troubleshooting codes are not failsafe.  The #1 Cylinder Misfire code often has an entirely different cause than #1 cylinder fuel or spark troubles.  On many PCM/ECM troubleshooting systems, the actual trouble masquerades as a #1 Cylinder Misfire code.  For insight, read through this topic at our forums:

http://forums.4wdmechanix.com/topic/73-40l-jeep-six-cylinder-1-misfire-trouble-code/.  

See if this information helps you find the root problem.  We can pursue the issue further...

Moses

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Hey thanks for the advice finally made progress in took my distributor and coil pack off and swapped them out cause they were under warranty rest the timing and now it fires right up 

20151229_105624.jpg

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Yea!  Glad you found the underlying problem...That should do it...Great looking Jeep YJ, should be reliable now...

Happy New Year, jjuststice85!

Moses

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