Mechanics

NEW MOTOR, NEW SENSORS, STILL P0171!!!!

1997 Ford F-150

Engine Performance problem
1997 Ford F-150 V8 Four Wheel Drive Automatic 204000 miles

Ok- My truck kicked the infamous p0171 codes and gave missfire codes on cyl 1 and suffered a major power loss though it has 35" tires with 4.10 gears. I replaced every plug/wire, new coilpack (though it was just a year old) replaced 02 sensors, new MAF sensor, new IAC sensor, new pcv valve, checked hoses for vacuum leaks, new fuel filter, ran seafoam through vacuum line from brake booster to smoke out the system. Still no improvement. I took it to the dealer who diagnosed that everything looked acceptable except cyl 1 failed the leakdown test. Suggested a new motor since the rings were probably shot. I had a new Jasper put in- idled better but still no power on hills/hard acceleration. I decided to go with catalytic converters. Temp tested between the 2 banks and bank 1 (pass side) was extremely hotter. Replaced both sides (all 4 converters) to be safe. Still no power improvement though I had no check engine light. One day later my CEL came on. Hooked it up and it's the same p0171 code saying Sytem Lean on Bank 1. I'm bank at the beginning though my bank account is almost $6,000 lighter. I guess Fuel delivery is my next route.
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Jmpowell1
October 3, 2010.



Why did they replace the engine? What was leaking down compression or fuel pressure?

This code simply means additional unmetered air is getting into the engine (By-passing the MAF). Usually, it's caused by a MAF but I see you replaced that. Have you thoroughly checked for vacuum leaks? There is a vacuum hose behind the throttle body that has a 90 degree bend and commonly dryrots.

Also, a faulty DPFE (mounted to the engine) can be the cause. It has two rubber hoses that go to the hose for the EGR. Many times corrosion in the sensor will cause it to under report EGR flow. What happens is the EGR is told to stay open longer causing a lean misfire. Yes, it sould set a PO401 (EGR insufficient air flow), but it is known to many times set the PO171 or PO174.

Let me know what you think. I have to admit, I'm not sure what all the dealer did, but I don't think you needed a new engine. This type of thing really upsets me.

Let me know.

Joe

Well the dealer didn't replace the motor. They only noted that cylinder 1 was showing much lower compression, like 60 lbs I believe. They also said that it was leaking down which was probably a sign that the rings were shot (Im assuming compression) and they suggested a new long block. This was after I had replaced all of the sensors and what not, so I figured this could possibly be where the misfire was coming from. If it had no compression to respond to the combustion, then the computer would read it as a misfire, this causing the lean condition on that bank. We decided cyl 1 was so shot that a new motor was needed anyways, and could be a cause for the power loss. So I took it elsewhere for the Jasper swap. Myself and a couple of family mechanics checked for vacuum leaks prior to the dealer visit. I had already changed the pcv valve and inspected the hoses/elbows coming from the pcv to the throttle body and around the EGR. Wouldn't the DPFE kick a lean code for both banks? Should I buy an injector and try it on cyl 1 since that is where all of my problems have shown? What about vacuum leaks on the brake booster? Wouldn't that cause both banks to read lean though?

Tiny
Jmpowell1
Oct 4, 2010.
From what I have delt with, the DPFE will cause a lean mixture on both banks. What it does is corrode inside. As a result, it doesn't sense properly and causes the EGR to stay open longer than it should. Thus, you get a lean mixture. As far as a vacuum leak at the brake booster, yes, it will cause a lean mixture on both banks.

I'm glad the dealer didn't take you. I would have done a wet compression test if it was a valve or the rings. Rings would have cost you a hundred bucks if you did it. As far as a valve, remove the head and reseat the valves. I just hate when dealers tell customers they need a new engine when it can be a cheap, easy fix. Sorry if I sounded upset.

Let me know if you have other questions. My guess is the DPFE is setting the code. Keep in mind, if you had a cylender that wasn't firing, the O2 sensors should have thought it was running rich because there would have been unburned fuel.

I'm here if you need anything. Let me know and I'll do my best to help.

Joe

Thanks so much for the quick replies. I probably should have looked more into the possibility of it being a valve. Esp since the catalytic converters on bank one clogged. However, I didn't have the time to put into pulling the head since I just moved and don't have a garage here and needed my truck back asap for work. I know that cylinder 1 was firing electronically, but I'm almost convinced there was an absence of fuel there causing the lean reading. I'm going to buy one injector tomorrow, disconnect the battery to reset the computer, pull the fuel rail and replace the injector on cylinder one. Hopefully that is going to be the root cause of everything. **Injector clogs/leaks, causes misfire, caused catalytic converters to clog after driving for way too many miles running lean while trying to troubleshoot, then the exhaust backed up, burnt the valve and caused the cylinder compression failure.** This is my theory anyways and I may be completely off. But I have way too many custom hours/money into the truck to turn back now. Yea I could have bought another truck for what I have into it, but atleast I will know what has been done to this truck! Any ideas if the new injector doesn't fix the problem?

Tiny
Jmpowell1
Oct 4, 2010.
Make sure there is power to it. Let me know what happens.

Joe

Ok so I went to Pep-Boys today and picked up a new BWD injector for cylinder 1. They were $10 cheaper than at Advance! I pulled out my toolbox right there in the parking lot and did the swap. Disconnected the battery prior to discharge any run-setting the computer may have stored for the misfire/lean condition. Cussed under my breath when the new injector wouldn't fit. Then found the old o-ring from the old injector was stuck inside the fuel rail blocking the new one. So I removed the o-ring, slapped in the new injector and fired it up. The " lub-dub" lope is still there sometimes at idle, but when I pulled out from the light it was as different as going from the stock gears to 4.10s! My truck has it's power back! (I think!) I cleared the code and I'm going to log some miles tomorrow to see if a code will show up again. I'm going to go ahead and order a complete set of rebuilt injectors for $100 and swap the rest out. The loping at idle I think may still be from the dpfe sensor. I'm going to pull the throttle body soon and go through the ports on the (3-year old) EGR and vacuum lines soon.

Tiny
Jmpowell1
Oct 5, 2010.
I hope that takes care of it. Keep me up to date.

Joe

Ok- so I logged about 200 miles on my truck last night and finally got to some hills where I noticed the power still wasn't where it should be. Soon the check engine light came on and now I'm back to square one. I'm going to scan it again. I'm assuming it's still the p0171 code, so should I be looking at replacing the DPFE now?

Tiny
Jmpowell1
Oct 6, 2010.
I would have it checked first.

Well I guess I'm taking my truck back to the dealer to have them reanalyze everything tomorrow. I'm just exhausted from playing the " that didn't work, try replacing this" game. I'm dying to see how this new motor will run when it's actually running on all 8 cylinders!

Tiny
Jmpowell1
Oct 10, 2010.
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