Topic: Not running good when cold

[k]

My Jeep is having a problem running when "cold".  It will start and sound good while not under load, but a soon as you put into drive (automatic) and apply the pedal, it will cough, misfire and even backfire.  Tried looking on line and at other posts for similair problems, but here is the kicker.  Unlike most that seem to start fine and develop problems as they warm up, mine clears up when it warms up.  There does appear to be a hesitation, but not at all what it does when cold.  Some other info, there does appear to be a small exhaust leak that quites down once it warms up also. 

What I have done so far...
1) Seafoam in the tank, crank case (30 miles then changed oil), and through a vacuum line, per directions.
2) Replaced IAS.  Thought it might be dirty.  Took it out and it came out in pieces (Backfire?).
3) Replaced plugs, some looked better than others.
4) Purchased compression tester, but have not gone through the paces yet.  Hopefully on the next day off.

Recent mods?
1) 4.o throttle body and spacer.
2) 19# injectors.
3) Sharp's adjustable FPR (Checked pressure.  It's good.)

Last item went in after Christmas, and the problem just started within the last month.  I have heard theories from MAP sensor to a bad lifter.  Any ideas?

[grumpygy]

Vaccum leak that seals up when it warms up.  Look at the areas you worked on.

[k]

Checked before, but will look in some less obvious areas.  Also might try spaying some throttle body cleaner around the vacuum connections to see if it causes a change in the RPM.

[sharpxmen]

Vaccum leak that seals up when it warms up.  Look at the areas you worked on.

vacuum leak won't make a difference unless it's on the MAP line.

My Jeep is having a problem running when "cold".  It will start and sound good while not under load, but a soon as you put into drive (automatic) and apply the pedal, it will cough, misfire and even backfire.  Tried looking on line and at other posts for similair problems, but here is the kicker.  Unlike most that seem to start fine and develop problems as they warm up, mine clears up when it warms up.  There does appear to be a hesitation, but not at all what it does when cold.  Some other info, there does appear to be a small exhaust leak that quites down once it warms up also. 

What I have done so far...
1) Seafoam in the tank, crank case (30 miles then changed oil), and through a vacuum line, per directions.
2) Replaced IAS.  Thought it might be dirty.  Took it out and it came out in pieces (Backfire?).
3) Replaced plugs, some looked better than others.
4) Purchased compression tester, but have not gone through the paces yet.  Hopefully on the next day off.

Recent mods?
1) 4.o throttle body and spacer.
2) 19# injectors.
3) Sharp's adjustable FPR (Checked pressure.  It's good.)

Last item went in after Christmas, and the problem just started within the last month.  I have heard theories from MAP sensor to a bad lifter.  Any ideas?

i can think of tps, temp sensor or even O2 sensor, but it's all guessing.

[k]

i can think of tps, temp sensor or even O2 sensor, but it's all guessing.
[/quote]

thought about the O2, but doesn't the ECM use information from that only after it warms up?  Not sure when the temp sensor falls into play, I think it lets the ECM know when to go from Open Loop to Closed Loop (right order?).  That might leave the tps and MAP sensors as likely culprits if it is sensor related.  I really hope that it is not a lifter.  Want to install the roller rockers and planned on replacing all the lifters then, just don't have the dough yet.

[sharpxmen]

i can think of tps, temp sensor or even O2 sensor, but it's all guessing.


thought about the O2, but doesn't the ECM use information from that only after it warms up?  Not sure when the temp sensor falls into play, I think it lets the ECM know when to go from Open Loop to Closed Loop (right order?).  That might leave the tps and MAP sensors as likely culprits if it is sensor related.  I really hope that it is not a lifter.  Want to install the roller rockers and planned on replacing all the lifters then, just don't have the dough yet.

if it was a lifter or a cam lobe you'd have that problem when warm as well and you'd be also hearing it.

ECM uses the o2 feedback once the O2 sensor is heated (warmed up) and not when the engine is warm - that is about 60 to 90 seconds from starting the engine.

the temp sensor would tell the ECM what mixture to target when cold (or warm), too lean and you'd be sputtering.

[k]

if it was a lifter or a cam lobe you'd have that problem when warm as well and you'd be also hearing it.

ECM uses the o2 feedback once the O2 sensor is heated (warmed up) and not when the engine is warm - that is about 60 to 90 seconds from starting the engine.

the temp sensor would tell the ECM what mixture to target when cold (or warm), too lean and you'd be sputtering.

Wouldn't the O2 sensor bring on a code?  (It does on my Ford anyway) CEL is not light, and does work.  It did go off earlier when I disconnected the vacuum to the MAP sensor.

[k]

CEL is not light,

sorry, I meant lit

[k]

Compression test completed, done cold relatively speaking (about 100* here today):
1st run                  2nd run
1) 150 psi              150 psi
2) 150 psi              155 psi
3) 140 psi              150 psi
4) 150 psi              150 psi

not bad.
Number 3 plug didn't look too good, and I had just replaced them.  Pulled distributor cap, and number 3 pin was not worn the same as the others...hum.
Performance Distributors cap and rotor on order. (Already run a Jacobs Coil and wires)
Unplugged MAP sensor and it actually ran better until it got into operating temp range, but will look at that more after replacing the cap and rotor.

[Torch_Ind]

can you get access to a scan tool to see what your sensors are saying when cold? 

[k]

can you get access to a scan tool to see what your sensors are saying when cold? 

closest thing I have is an Autozone.  I know they can pull codes, but don't know if they can scan.  Defeats the purpose though, unless they will let me take it home, it will be too warm when I get there!     Can't have a normal problem that acts up when warm!

[sharpxmen]

try this (PCM temp sensor is on the thermostat housing)



ENGINE COOLANT TEMPERATURE SENSOR TEST
To perform a complete test of the engine coolant
temperature sensor and its circuitry, refer to DRB
scan tool and appropriate Powertrain Diagnostics
Procedures manual. To test the sensor only, refer to
the following:
Disconnect wire harness connector from engine
coolant temperature sensor (Fig. 33).
Test the resistance of the sensor with a high input
impedance (digital) volt-ohmmeter. The resistance
should be less than 1000 ohms with the engine at its
correct operating temperature. Refer to the Coolant
Temperature Sensor/Manifold Air Temperature Sensor
resistance chart. Replace the sensor if it is not
within the range of resistance specified in the chart.
Test continuity of the wire harness. Do this between
the Powertrain Control Module (PCM) wire
harness connector terminal-2 and the sensor connector
terminal. Also test continuity of wire harness terminal-
4 to the sensor connector terminal. Repair the
wire harness if an open circuit is indicated.

[k]

Sharp,

try this (PCM temp sensor is on the thermostat housing)



I will need to get a volt meter.  I was in constuction before, my auto tools are limited to wrenches and sockets mostly...

In the mean time, here is a pic of the plugs...

[k]

opps.  let's try the pic again...

[Torch_Ind]

opps.  let's try the pic again...

wow 3 of them look like they got way to hot. discolored and warped ends

try the old plugs again maybe you got bad ones