88 Comanche slow to fire and surging once in open loop

[golddigger]

Good morning I ham beating my brains out chasing a problem 

the truck is a 4.0 82k miles automatic transmission.

it will be slow to fire  probably 4-5 revolutions. then it will fire. it will run decent until the truck goes into closed loop then it will have a slight surge when idling  I can hear when it goen into closed loop  as the rpms will drop down real low than it will go into surg mode.

it also has a slight stumbling issue at the start of the throttle range maybe 20 percent in 

while under a load or under acceleration it seems to run fine  just at cruzing speed about 45 mph,  or in nuetral about the same thottle  

what i have replaced.

Mullfer 

Cat   (was plugged)

02 sensor

TPS

Fuel filterr

spark plugs

map sensor 

Crank position sensor

 

mods

firewall ground direct from battery cleaned paint assed no-ox 

 

[pizzaman09]

I'd check to see if your header bolts are tight.  Also check to see if all of your header studs are still present, particularly the ones near the back of the head like to come loose and even back completely out.

[golddigger]

On 5/18/2025 at 9:28 AM, golddigger said:

Good morning I ham beating my brains out chasing a problem 

the truck is a 4.0 82k miles automatic transmission.

it will be slow to fire  probably 4-5 revolutions. then it will fire. it will run decent until the truck goes into closed loop then it will have a slight surge when idling  I can hear when it goen into closed loop  as the rpms will drop down real low than it will go into surg mode.

it also has a slight stumbling issue at the start of the throttle range maybe 20 percent in 

while under a load or under acceleration it seems to run fine  just at cruzing speed about 45 mph,  or in nuetral about the same thottle  

what i have replaced.

Mullfer 

Cat   (was plugged)

02 sensor

TPS

Fuel filterr

spark plugs

map sensor 

Crank position sensor

 

mods

firewall ground direct from battery cleaned paint assed no-ox 

 

Ill get after it   

I am also looking for a air temp sensor 

[89 MJ]

Did you make sure your TPS is adjusted properly? These Renix Jeeps take a little bit longer to start than a newer vehicle. 

[golddigger]

1 hour ago, 89 MJ said:

Did you make sure your TPS is adjusted properly? These Renix Jeeps take a little bit longer to start than a newer vehicle. 

thank you for your reply Carter 

I did adjust it correctly my input /base voltage is 4.96 and I adjusted it accordingly 

strange thing last night happened, 

I was checking the sensor plugs and found that when the air temp sensor is unplugged it will stop the stumbling even while driving yet there is still a small surge at idle. 

I need to find the unicorn sensor   for the air temperature.

any help will be greatly appreciated 

 

thank you  

John

[golddigger]

On 5/18/2025 at 6:03 PM, pizzaman09 said:

I'd check to see if your header bolts are tight.  Also check to see if all of your header studs are still present, particularly the ones near the back of the head like to come loose and even back completely out.

thank you  Pizzaman