My CEL just came on about a week ago displaying Codes PO171 and PO174. Message on my OBSII Scanner said lean on banks 1 and 2. Where do I start and in order of what priority. The vehicle is a 97 4X4 Ranger 4.0 with automatic and 97,000 miles

Thanks for any help anyone can lend.

 

The first thing to check for is a vacuum leak.
Check for cracked or broken vacuum hoses.
Check around the intake manifold gaskets.
If you dont find any thing,clear the codes and
drive to find out how quick it comes back.
Have also seen o2 sensor set this code but
not both sides at once.
Hope this helps.

Mike

 

Thanks Dr No

Kinda had a feeling thats where I would be starting based on different information I've been assembling since the CEL came on.

 

Need some help. Posted a thread about 2 months asking for help in troubleshooting codes PO 171 and PO 174. (Banks 1 and 2 both lean.) Received 1 response to the thread to check for a possible vacuum leak somewhere.

I have more information now.

Vehicle is a 97 Ranger with a 4.0 and automatic transmission. Vehicle starts up OK either when hot or cold and idles fine during the entire warmup period. The problem occurs after vehicle has reached normal operating temperature. It appears to run OK under a load and at highway speeds, even though it does not seem to have the power it used too but when coming to a stop the engine will lobe very badly and sometimes will stall. It needs additional accelerator to keep from stalling. This lobing condition will last for maybe 10 or 15 seconds then the engine will return to a normal idle ( about 550 RPM in gear.) It will idle smooth for maybe 30 seconds and then start lobing badly again. This cycle continues to repeat itself.

Sure would appreciate any help.

 

Did you ever check for vacuum leaks? The 4.0 can have problem around the intake gaskets. What is the engine vacuum? Do you have any exhaust leaks?

 

Ken00
Have spent a little time checking for vacuum leaks around hoses and PVC value. Not sure of what a good procedure would be for checking for vacuum leaks. Could you advise?

Also have noticed a good amount of rusting on exhaust manifolds. Very good chance there could be a leak there. What should the engine vacuum read?

Thanks

 

On a cool engine spray carb cleaner around the gasket areas, if the idle changes there's a leak.

Rusty manifolds won't be a problem since they are thick cast iron.

around 15-17, steady.

 

Thanks Ken for the help and your time. Will give it a try today.

 

My 97 4.0 Ranger had this problem (for a few years). I finally decided to change the plugs & wires. EGR was in two pieces (rust) so I decided to take it to a shop. I has around 100k miles. After this work was done, it still ran rough. The Mech, said the upper intake manifold gasket was leaking. He was able to verify it by spraying around the suspected area. The spray sucked into the gasket area and the engine ran fine for a few seconds.

I had the gasket replaced and the truck runs like new.

Kenny III

 

Thanks for the reply Kennyiii. I got tired of fooling with a few months ago and finally took it in to the shop. They told me the same thing that you did. Bad upper intake manifold gasket. They replaced it and it's run fine ever since.

Thanks...

Redtruckdude