4.0L OHV & SOHC V6 Tech General discussion of 4.0L OHV and SOHC V6 Ford Ranger engines.

Intake and exhaust mods turned check engine light on ?

  #1  
Old 12-06-2018
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Intake and exhaust mods turned check engine light on ?

I recently installed a cold air intake and a complete 2.5 inch exhaust with a magna flow rear cat . On my 2005 Ranger 4.0 I took it for a test ride, 16 miles in the mil [check engine light came on, code reads po174 lean burn right bank lean burn left bank. Will this clear with putting miles on? Or will I have re tune the PCM?
 
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Old 12-07-2018
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Welcome to the forum

P0174 just means Lean on Drivers side bank
Do you have a 2nd code?
Like P0171

Lean code on both banks would be related to the new CAI, Ranger already had a CAI which works fine, just FYI

Lean code means computer is having to add at least 20% more fuel that it calculated based on air flow reported by MAF sensor.

I assume you are using stock 4.0l exhaust manifolds and did the 2.5" pipes from there back

If you are using non-stock headers then check for leaks at the heads, exhaust leaks there suck IN air, which causes Lean readings at O2 sensors, a false Lean
So that could just cause the one Lean code
 
  #3  
Old 12-07-2018
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Thanks for the input RonD I thought as much that two codes would of had to be turn on but not always true for both banks to come up as lean burn. I have access to ALLDATA pro not much info under po174 it refers to look under po171 for possible causes. On line po174 comes up as right bank lean and po171 left bank lean.My OTC code reader is saying both right and left lean burn. On ALLDATA some of the possible causes are the obvious ones, MAF, vacuum leaks, fuel filter, fuel pressure, intake leaks, PVC, EGR, and the most interesting one was Air induction turbulence due to an incorrect air filter. But not any thing regarding the exhaust system. ALLDATA also said once the PCM reaches 15% in trying to correct Fuel trim it kicks a MIL code. I installed an AFE cold intake at the same time as the exhaust install. AFE teck said I need to put as much as 200 miles on upgrades to reprogram PCM . I only have driven as to date about 85 miles on the upgrades. Just wondering if if more miles will allow for a correction? In the mean time I am check out what came up on ALLDATA list Replacing fuel filter, checking for vacuum leaks, swapping out the MAF, and so forth. Just wondering if any body out there actually had a problem like this and if drive time self corrected it. I replaced the exhaust back from the rear cat leaving the stock exhaust and two front cats intact ed. From rear cat back 2.5 inch pipes with a Walker 2.5 inch high flow stainless steel system ' Best Regards Big foot Ranger
 
  #4  
Old 12-07-2018
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There are two fuel trims

Short term fuel trim(STFT) is the real time changes the computer is making to the Open Time of the fuel injectors
Computer gets precalculated air flow from a Table in memory for a 4 LITER engine at specific RPM and Throttle position
It then off sets this by MAF sensor air weight reading and air temp reading, and thats 0 STFT open time for an injector
That air/fuel mix is burned and computer gets result from O2 sensor
If O2 shows too much oxygen, thats a lean burn, computer then sets +2% STFT, and that mix is burned, if O2 still shows lean then +4% STFT, ect...... until O2 shows correct oxygen levels
This only takes a few seconds
If there was not enough oxygen in exhaust then that would be a Rich burn, and computer would try -2% STFT, then -4%, ect.........

And it is a percent, if STFT 0 had a fuel injector open for 100ms(milliseconds), then +2 would be 102ms open time, -2 would be 98ms open time

Yes, if STFT stays at +15%(or -15%) for awhile computer can set a code, but generally it needs to be 20% difference


There is also LTFT(long term fuel trim) which is "learned" over time
LTFT is used because engine systems get older, there will be air leaks and fuel pressure will go down a bit over time, so LTFT allows computer to adapt to changes over time.

If STFT was always running at +5% then over a few weeks LTFT would be +5%
Each time you restart computer it has LTFT in memory, after it does its calculations it then applies LTFT to it, so calculated 0 STFT is actually 0 + 5%, so STFT would show maybe +1% with engine running, but it is actually +6% because of small air leak or lower fuel pressure.

So yes if your LTFT is low now then it may go higher and "relearn"

But cold air intake and your exhaust mods shouldn't have changed anything

Cat back just changes the sound of the exhaust, so shouldn't change anything engine wise unless you block the exhaust flow

You already had a cold air intake, so changing that wouldn't change anything either.
Best bet is that something is wrong with installed cold air intake.

The MAF sensor WEIGHS the air coming in
14.7:1 is the air:gasoline mix ratio, and it is a WEIGHT RATIO
14.7 POUNDS of air to 1 POUND of gasoline
14.7 grams of air to 1 gram of gasoline

Gasoline's weight doesn't change much cold or warm, but air's weight changes a lot

Cold air is heavier than warm air, i.e. "hot air rises", why?, because it is lighter than colder air
At Higher elevation air is "thinner" so lighter
The computer needs a way to WEIGH the in coming air, that is what MAF sensor is for
It has a heated wire inside, the wire is cooled by air flowing past it, colder heavier air cools it more, also faster flowing air
MAF only samples 10-15% of the in coming air, just FYI

If you have turbulent air flow past the MAF sensor then WEIGHT would be wrong, it would under report air's weight so computer would add LESS gasoline and get a Lean burn, so would have to increase Open Time, and get to +15-20% STFT

So I would start there
 
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Old 12-07-2018
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Thanks much RonD what you have said is true as true can be. and is what I understand, The install I double checked that all boots were on correct and tight ,not alot to an install for a cold air intake. I 'm going to check for vacuum leaks then take it back out on the road and check the live data I will reply back after I have the data Thanks and Best Regards
 
  #6  
Old 12-08-2018
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Hi RonD thanks again you are very knowledgeable. I had another question . Are you saying that the stock intake was already a cold air? Changing from the stock intake to an after market performance intake in this case a AFE along with changing the rear cat to a 2.5 inch along with the exhaust back to the tail pipe all 2.5 inch has to increase air flow. Does it not? And in doing so would there not also be more air turbulence past the MAF ? Especially with a modified filter. Just trying to rap my mind around the changes that might have occurred after the mods were done.
 
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Old 12-14-2018
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Hello RonD just wanted to share some addition info on a check engine light being turn on after installing an after market performance cold air in-take. 1st I have to say you were absolutely right on in calling the problem . Going the long way around the block, here's what all I did to isolate what was going on.

To find out why my check engine light keeps coming on with codes po171 and po174 lean burn right and left bank codes after I installed the afe cold air in take on my 2005 Ford Ranger 4.0. The diagnostics we did were. 1st replaced the fuel filter , checked fuel pressure. 60 to 65 lbs checked the TPS along with the MAF. and the PVC, EGR . Then we checked the intake system for vacuum leaks with smoke. We also checked out if the o2 sensors were working right by enriching with propane and they where working right. The live data before and after the parts mentioned, did not change. The Long term fuel trim was maxing out at idle 25.0 both banks, then when you would rev the engine the Long fuel trim would go down just the opposite what it should have been doing . So we reinstalled the stock air in take, and took it for a test ride. The long term fuel went down 1to 3 at idle and when up like it should when the engine was revved. I drove it for 60 miles checking the live data all the while test driving it all within ranges . So we reinstalled the afe in-take and the live data went right back to where it turn on check engine codes. I have several hundred miles on the truck after I installed the afe in-take, plenty time for the ECU to relearn and it was not able to re Map. My conclusion was this In- take will not work on this application... In doing the diagnostic due diligence we were able to figure this out. As I took another look at the stock air in-take I have to say there's not much out there if any thing. that is better in being an actually cold air in-take. All the after market in-takes draw air in from in side the engine compartment. the stock air in-take actually draws air from outside the engine compartment, It might be way better to just up grade the filter in the stock air box . Thanks once again RonD for pointing me in the right dirrection. Best Regards Leo J
 

Last edited by Big foot Ranger; 12-14-2018 at 09:45 AM.
  #8  
Old 12-14-2018
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Good work

Thanks for posting the tests done and results

MAF sensors only sample 10-15% of the incoming air, not sure of the exact % but that really matters because computer is using the exact % as a multiplier to calculate in coming air

If there is any kind of turbulence or diversion of air flow around the MAF sensors location then the under reporting of air flow error is multiplied by maybe 10, so makes a big difference in final calculation

i.e. if its 10%, If MAF shows 1 cubic foot or air passing by then computer uses 10 cubic feet of air in calculation, if .9cu/ft then 9cu/ft so big differences with small changes
 

Last edited by RonD; 12-14-2018 at 09:58 AM.
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