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Hello again everyone. I have a 1996 Deville with 117,000 miles on it and I am getting two codes popping up which are a PO171 and a PO174. These two codes are a lean bank 1 & 2. I have tighten down the intake manifold, put a fuel filter on, checked for vacume leaks and made sure I didnt have bad gas. Nothing has worked, what should I check or do next. It seems like when the weather gets real cold these codes pop up. Thanks everyone

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Your codes point at a vacuum leak that is common to all cylinders. Keep after the vacuum hose situation and since it is weather/temperature related, pay extra attention to plastic elbows, tee fittings, and nipples.

Maybe a stethoscope would help??

Jim

Drive your car.

Use your cell phone.

CHOOSE ONE !

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What have you done to check for vac. leaks? Have you made sure that the intake(into the throttle body)is sound?

I have inspected all vacume lines on the top side of the engine, visually. Yes the throttle body to the intake is sound, I put a new gasket in.

Jim, I will check all the elbows and plastic fittings. I dont know if this will help but my idle RPM'S are at 600-625 in gear with the brake on.

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I replaced all elbows and plastic fittings, they didnt look bad but better to be safe than sorry. I did check everything between the air filter and the throttle body, the screen by the MAF sensor was clean and what I could tell the MAF sensor itself looked good.

Ranger, the PCV fitting in the rear cam cover seems loose. Could this cause a PO171 & a PO174? I will replace this fitting tomorrow.

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:P :P Oh, Well when I indicate "plenum" I'm getting at the intake between the air breather and the throttle body..

Oops! I didn't read it close enough. I saw "plenum" and automatically assumed you meant THE plenum on the 2000+ engines. Sorry for the misunderstanding.

Ranger, the PCV fitting in the rear cam cover seems loose. Could this cause a PO171 & a PO174? I will replace this fitting tomorrow.

Yes, if the rubber grommet is loose enough it COULD cause those codes.

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When i replaced the wires on my '94 STS I broke the rear cam cover Pcv tube (brittle plastic) and spliced it with apiece of 3/8" fuel line,itseems to be working fine,although I think that I might just run afull length of 3/8" hose to repair...

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Now we have just a PO174 code with the service emission message across the bottom gauge cluster with no service engine light on. Does this mean I need to replace the front camcover fitting? Thanks

Edited by heitzman
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P0174 - Fuel Trim System Lean Bank 2

Anything on Bank 2 that can leak vacuum only to Bank 2, that includes

Intake manifold gaskets

Check these links

http://caddyinfo.ipbhost.com/index.php?showtopic=17226&st=0&p=122871&hl=P0174&fromsearch=1entry122871

especially this one, notice the list of things I posted to check

http://caddyinfo.ipbhost.com/index.php?showtopic=21056&st=0&p=142124&hl=P0174&fromsearch=1entry142124

Pre-1995 - DTC codes OBD1  >>

1996 and newer - DTC codes OBD2 >> https://www.obd-codes.com/trouble_codes/gm/obd_codes.htm

How to check for codes Caddyinfo How To Technical Archive >> http://www.caddyinfo.com/wordpress/cadillac-how-to-faq/

Cadillac History & Specifications Year by Year  http://www.motorera.com/cadillac/index.htm

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Does anyone have any other ideas?

P0174 - Fuel Trim System Lean Bank 2

Since you are now down to a trouble code that points at bank 2 (front bank) I would say you have repaired all the sources of vacuum leaks.

The next logical step here (for me anyway) would be to suspect one or more dirty, partially clogged fuel injectors. If it was my car, I would run two tanks of the highest octane fuel you can buy from a top tier gasoline retailer. The detergent levels in top tier fuel might be enough to remove nasty deposits from your fuel injectors.

Top tier retailers include Chevron, Exxon, Shell among many others. Do a search on top tier retailers.

If that fails to produce results, I would try a can of Techron concentrate; be sure to follow the instructions to the letter. I am not a fan of additives, but recommended levels of Techron concentrate can produce results without doing any damage to the fuel pump motor windings.

Jim

Drive your car.

Use your cell phone.

CHOOSE ONE !

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I checked the O2 sensor and harness all is well, it was replaced less than 6 months ago. No exhaust leaks. I did put a couple of hose clamps on the hose fitting to the front cam cover upto the throttle body. I also went and purchased a bottle of Techron concentrate and filled the tank up with gas. So we will see what happens now, I think everything has been covered except the O-rings on the injectors but I will see where we are at with what I have done so far. Thanks again everyone.

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That's great, so the P0174 code was brought on by a clogged injector, I guess?

Pre-1995 - DTC codes OBD1  >>

1996 and newer - DTC codes OBD2 >> https://www.obd-codes.com/trouble_codes/gm/obd_codes.htm

How to check for codes Caddyinfo How To Technical Archive >> http://www.caddyinfo.com/wordpress/cadillac-how-to-faq/

Cadillac History & Specifications Year by Year  http://www.motorera.com/cadillac/index.htm

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I am thinking your right bodybyfisher. It had to be a clogged injector or maybe that tube that runs from the front cam cover to the throttlebody. But anyway I really appreciate the help and thanks again.

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Well I am glad we could help

Pre-1995 - DTC codes OBD1  >>

1996 and newer - DTC codes OBD2 >> https://www.obd-codes.com/trouble_codes/gm/obd_codes.htm

How to check for codes Caddyinfo How To Technical Archive >> http://www.caddyinfo.com/wordpress/cadillac-how-to-faq/

Cadillac History & Specifications Year by Year  http://www.motorera.com/cadillac/index.htm

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Applying several fixes at the same time can mask the actual "problem". But when you need the car on the road, you need the car on the road. I understand and applaud the repair approach.

My money is on the Techron that cleaned up one or more dirty injectors.

Thanks for the feedback and continued Happy Motoring!!

Jim

Drive your car.

Use your cell phone.

CHOOSE ONE !

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