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On start up, give it gas it dies...

Bdiddy11

NAXJA Forum User
Location
Boise,ID
I've got an 87' Chief, automatic, approximately 165k miles or so on it. I just did a partial tune-up w/new plugs/wires and cleaned the dist. Haven't done the oil change yet but will do that here shortly. Also ran some seafoam through the TB and in the gas tank. Has plenty of oil in it too...

Here's the issue... when I go to start up the Jeep in the morn, it cranks over, idles, and if I hit the gas it will either die or try to die on me. Only when I let it warm up for about 5+ minutes can I then hit the gas and drive it normal. Even when I start it up, and put it in reverse it will die on me w/out letting it warm up. I'm really confused at what the issue is or where to start. It's also got a new battery because mine wasn't holding a charge.

I was having these issues long before I did the partial tune-up and even when the weather was a lot nicer.

Any ideas on where I should start checking?
 
If the map sensor is inoperative you could have these symptoms. First thing is to check that the vacuum hose is connected to it.
 
Any other ideas...? Would it be best to try a junk yard MAP sensor to see if that's the issue or just get a new one?

instead of just replacing parts, you need to test the sensors with a meter. go to www.lunghd.com and go to on site tech. on site tech has a section for sensor diagnostic for non HO engine(renix)
 
Okie... so the hoses seem to be fine and connected to the MAP sensor. I went to the junk yard and got two other sensors to test them, and used a digi-multimeter as well, still having the same issue.

Any other suggestions on what this might be? I give it gas... and it will either die or try to die on me. Only way it doesn't die on me is if I let it idle for about 5 or so minutes. I'd like to get this taken care of as it's a pain in the butt in the afternoon when I want to get out of work but i've gotta wait to let the Jeep warm up so it doesn't die on me when I try to pull out into traffic giving it gas.

Thanks.
 
I'd try testing the coolant temp sensor. If it is bad, it can send a bad input to the computer which could result in an improper fuel mixture, which could result in cold driveability symptoms. It is an often overlooked sensor.

The coolant temp sensor can be checked with a simple meter. Best way to do it is to remove the sensor and place it in a beaker of water and test resistance with temp verified by a calibrated thermometer, but simple and dirty, you can test the sensor in the vehicle and get a fairly good idea of your sensor is working. Refer to the link in the earlier post for more info.
 
I took a picture of what I think is the coolant temp sensor.. I'm still a novice with knowing parts in the engine bay...


tempsensor.jpg


Is this it?

87' Chief, Automatic.
 
The sensor you have there is the intake manifold air temperature sensor (MAT among other names). They get coated in oil an occasional cleaning (gently) can be helpful.
The engine temperature sensor is on the lower left of the block near the front and is actually much the same sensor as the MAT. First thing in the morning before the motor has been started, do an ohm test on the MAT and the engine temperature sensor, they should have nearly the same resistance.
Maybe clean the IAC, at the least squirt some spray oil down the orifice for the IAC. Though it likely needs a cleaning. They aren't real difficult to clean, remove them being careful of the "O" ring seal. I usually scrape off as much junk as possible gently and do the same for the seat in the TB, then use a little spray oil to loosen the rest and wipe it off with a rag or Q tips. Let a few drops of oil run behind the piston in the IAC, I use regular old synthetic motor oil, though a short squirt of spray oil may be as good. I wouldn't give the IAC a bath in spray oil or solvent, it is actually a ting little electric motor. Clean the connector pins up good with a contact spray.
This may be your problem it may not, but the IAC needs periodic cleaning anyway. Don't mess with the IAC piston, tiny little gears and teeth in there, if it is pulled out too far, the piston will launch half way across the garage (there is also a spring in there).
 
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Brian,
Sounds to me like it may be an O2 sensor.
 
Hey Commando where ya been? =) I shot you a PM not too long ago.

An 02 sensor... poo stain. Guess I should read up on how to test that too.
 
I did a test on the O2 sensor from Lunghd's site. The first one testing A + B terminals. It came up with a reading of about 13 OHMS... what's that mean? Is it a bad O2 sensor that could be causing these problems... or just part of it?
 
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