1996 F150 5.0L throwing fuel rich codes on two banks.

Check Engine light is on.

Engine just pulled, rebuilt and reinstalled.

Following also replaced:

Injectors
Radiator
Water pump
All belts and radiator and heater hoses
Motor mounts
Throttle body
Catalytic converter
Muffler
Plugs and wires
All filters
Mass Airflow Sensor
All 3 O2 sensors
Thermostat
PCV Valve
EGR Tube
Bypass hose
Starter solenoid
Oil pressure sending unit
DPFE Sensor


My "mechanic" has given up trying to determine the cause of the Fuel Trim running between -7% and -20% intermittently on both banks and the Check Engine light.

So please HELP!!!

 

What codes are present?

ave you checked fuel pressure?

What injectors did you buy?

 

Vacuum leaks? My 96 threw codes for both O2 sensor banks and it turned out that the rubber elbow at the evap solenoid was split.

 

I'm sorry, I don't have the specific codes. My OBD scan tool won't be here until tomorrow.

I stopped by Autozone and had them read the codes with their scanner and didn't write them down. I'll either go back there today and ask them to scan it again and write down the codes, or I'll post them tomorrow when the BlueDriver scan tool arrives.

The "mechanic" checked the fuel pressure and said it was good. (I had suggested that perhaps the fuel pressure regulator needed to be replaced. He said he checked the pressure and it was good.)

As for the brand of injectors, I don't know. He ordered them and put them on. All I can tell you is that they are yellow.

He made the comment that they looked identical to the ones he took off. (Which he was supposed to save for me, but didn't.)

 

I would suspect either high fuel pressure, incorrect injectors, or a MAF problem.

When you get the scan tool, can you post the coolant temp it reports as well?

 

Fuel pressure is as follows (according to the mechanic):

35 regulated
45 unregulated

 

I assume that means vacuum line on/off. Those numbers seem okay, maybe a little on the high side, but nothing that'd cause a -20% fuel trim.

 

I think you're right in your assumption.

I'm going to go and get a fuel pressure regulator and we're going to put that on and have him rescan everything. And I'll get the codes and post them.

This is actually it's more about the exercise of having him put it on and then check all of his work while I'm standing there than the part itself.

I also asked about the injectors.

These are the ones he put on:

http://www.amazon.com/gp/aw/d/B01BLT...rds=e2tz9f593a

I'll provide an update after the regulator is swapped out and I get all the codes.

Thanks a bunch for all your help!

 

EGR possibly hanging open?
It would be like a vacuum leak, but its letting in oxygen deficient exhaust gas into the intake making it run rich instead of oxygen rich air to make it lean out.

 

P0172 System Too Rich (Bank 1)
P0175 System Too Rich (Bank 2)
P0232 Fuel Pump Secondary Circuit High

Last one is new after replacement of fuel pressure regulator.

Fuel pressure at rail after regulator replacement 30 at idle up to 40 under acceleration.

Coolant temp 199

 

I'd suspect either a MAF problem, or incorrect injectors then. Are both O2 sensors reading a high voltage? High would be over 0.500 volts, usually around 0.7-0.9 volts.

 

I had the same issue last year and couldn't figure it out, so this may help or not. It was about six months until I had to get the truck inspected so I wasn't too worried about it. I decided to take care of a few other issues I had at the time, one being the brake booster was making a hissing sound (leaking) and was continually getting worse. I ordered one from Rockauto, put it on, and my codes disappeared. I would have never thought that it would be the cause of the codes, but here we are.

 

Took the truck for a 30 mile round trip. I drove, mechanic monitored the system with his SnapOn diagnostic tool.

O2 sensor voltages went up and down indicating proper functioning according to him.

Water temp 199
Baro 151

Short term fuel trim on both banks moving within +-5 and +-7 ranges.

But long term fuel trim still showing -17 and -21.

Tested for possible EGR valve hanging open/closed by using vaccum pump to manually open/close it. At idle truck would go from running smoothly to almost dying when state of valve was changed manually.
Test indicated it was working properly.

Injectors used claim to be a direct replacement for the Ford part # injectors that were replaced.

Turned check engine light off about 15 miles into our trip and it has not come back on. I've driven it probably 50 miles after he turned it off and it hasn't come back on.

The truck seems to be running fine.

But the long term fuel trim #s are still out of whack while the short term numbers seem to be in the acceptable range.

My own scan tool will be here tomorrow. I'll take some readings and also see if the check engine light comes back on.

I'll post what I find out.

Thanks again for all of your help.

 

The long term fuel trims are excessive, but the short times varying around +/- 5% indicates the computer was able to successfully pull enough fuel. I personally think the injectors were a little out of whack.