4cyl 2.5 Ranger rough idle sometimes CEL
Posted in the Ford Ranger Forum
#1 Jan 24, 2010
I have replaced both o2 sensors, plugs, wires, and air filter. I have a CEL for bank one lean. sometimes it idles rough and sometimes idles fine. I cant figure out whats wrong. It also has an aftermarket cat the owner before me had put on. The truck is a 1998 Ranger with a 2.5 4cyl and 105xxx miles. Im getting 24mpg. I have had people say maybe its a bad intake gasket but i have sprayed everywhere with carb clean and idle does not change. Someone help me inspections coming up.
#2 Jan 24, 2010
Oh also i thought i should add it starts hard in the cold. If i remember correctly in the summer it started fine (check engine light was on then also)
#3 Jan 24, 2010
One bank lean could be due to dirty injector. Unscrew plugs and see if one is whiter than other 3. That's where injector got dirty. Don't waster your time and money trying to clean it, just get a new on the internet and swap yourself (easy weekend project).
Cat has nothing to do with either problem. Engine doesn't care about cat for drivability, there is just a cat monitor test for liberal greenies.
#4 Jan 25, 2010
Ok I will probably do that tomorrow. If one is dirty can I run that Techron in the tank and maybe try to fix it?
#5 Jan 25, 2010
****If one is dirty can I run that Techron in the tank and maybe try to fix it?****
I don't believe so. Gasoline is a potent solvent and being run through injectors at high pressure (55psi). If it doesn't solve gunk (that looks like hard epoxy), nothing will without destroying injector. Techron may provide a temporary relief, but no more than that. I tried to clean injectors in techron in ultrasonic cleaner for more than a day (I took them off). They worked for about 15000 miles and I got misfire again. In my view, it's easier to get a new injector for ~50$ and forget about it for ~100000 miles, but it's up to you.
BTW, check the fuel pressure at the rail (borrow gauge at autozone for free), should be 55psi+, if it's too low (<35psi), the pump might be going south (pressure regulator built into the pump starts to leak).
#6 Jan 26, 2010
Ok thank you. i an VIP near me that loans out tools maybe they have one i can borrow. I will check the plugs today it is fairly nice out.
#7 Jan 26, 2010
i pulled all of the plugs and they were all the same color and the right color.
#8 Jan 26, 2010
Then my next guess would be fuel pressure at the rail.
If fuel pressure is good, I would borrow a OBDII scanner from autozone (free), the one that can read live stream data. Watch the O2 sensor output or SHRTFT (short fuel trim PID) in both banks. Normally it should oscillate about 0. See if there is any difference between banks. If there is, may indicate bad oxigen sensor (if it's just lazy, it won't set O2 sensor specific code). Then look at LONGFT in both banks at idle. If it is positive much more than 20%, you may have a leak. If you crank throttle to 2500 rpm, LONGFT should drop some. If the delta is more than 15%(let's say, 30% idle, 10% at 2500rpm), you definetly have a leak and need to start snooping some more. Add SHRTFT to your calculations, if it's not average zero.
Possible air leak point: IAC (idle valve stuck open or closed), try to unscrew it and spray with carb cleaner. Purge canister solenoid may stuck open - that would set evaporative leak code. Check vacuum with a gauge from autozone - should be -22psi. Just listen for some hiss...
#9 Jan 26, 2010
Well i called the autozone near me they have a fuel pressure tester to rent for free with 150$ charge that i get back. I don't have school Fridays so this Friday ill go to them. And my truck is the 2.5 4cyl, there is only one bank, because i noticed in the message you were mentioning 2 banks (just fyi). And also i have replaced both oxygen sensors. I'm confused with the numbers and percents that you are describing but im sure once i get that tool I will understand. One last thing, i looked in my hanes repair manual that i just picked up today that my fuel pressure should be with key on and engnie off between 35-45psi and at idle with vacuum hose connected between 25-35 psi. Just thought i would let you know because you thought it was 55+psi.
Thanks a lot for your help so far
#10 Jan 26, 2010
That one bank thing really threw me off... Usually, when only one bank lean, it means injector got clogged... unless it's one bank engine.
Ranger up to 97 had pressure regulator in engine compartment with return line going back to the fuel tank. These are supposed to have 35-45 psi at the rail, 25-35 with regulator on. Starting 98 they began to use high pressure pump with regulator built in the pump. See if you have return line from regulator, if yes then go with 35-45 numbers. If no return line, then the pressure should be 55+ and not dropping. If it's less and dropping, the pump reg (little rubber ball on a tiny spring) stuck open, or you got leak in connector hose in pump assembly (or both).
SHRTFT PID is a short fuel trim in response to O2 sensor. LONGFT PID is long term fuel trim correction. Positive value at idle means it takes more fuel to achieve proper fuel mixture, which could be leak. When it hits 40%, you get bank lean code posted. When you open throttle, leak becomes less relevant and LONGFT value drops. Difference more than 15% is considered out of spec, means big leak.
See if your code reader shows any freeze frames. If lean condition at low rpm, it's more like leak. If lean condition at high rpm/high engine load, it's more like low fuel pressure.
#11 Jan 27, 2010
well it only has one bank because their is only one exhaust side, because its a 4cylinder. And Friday i will be going to auto zone to borrow the fuel pressure tester. I get paid Thursday so i don't have the money right now.
#12 Jan 29, 2010
OK well i went to autozone and rented the fuel pressure tester but its 10 out and extremely windy so im not doing that now lol. But while i was there i asked to borrow a scanner and got TWO codes...before i only had one. I used to just have a P0171 now i also have a P1401. P1401 is not even in my Hanes repair Manuel.
On a side note remember when I told you my truck has an aftermarket CAT on it because the old one must have rusted out? Well whoever put it on did not reconnect the DPFE sensor, thats the one with 2 hoses and an electrical plug on it i think right near the exhaust manifold. Anyway about 2 weeks ago I noticed it and connected it to the plug that was dangling next to it. I was so happy because I thought I had found the problem. But after connecting it, the truck ran EXACTLY the same so I was bummed..:( but now that that is connected im guessing thats what the P1401 code is. Can you help me?
#13 Jan 29, 2010
I know they disconnected it because they took off the exhaust manifold to do the CAT and weld it all up and that sensor is bolted to the manifold. So they removed it and unplugged it.
#14 Jan 29, 2010
Oh also i thought i should add something else lol. After driving home from the autozone after eight miles the CEL came back on, i scanned that and the P0171 code was back, but not that other one. I guess maybe the computer just hadn't checked that sensor yet, because its only been 8 miles.
(sorry for adding 4 separate things and not all at once)
#15 Feb 1, 2010
You are right, P1401 is that emission gas recirculation EGR sensor. It could be because it was disconnected. Sometimes it posts intermittent code on old cars, because it senses exhaust pressure and may get worn out.
That made me think about one more thing. If there is a leak in exhaust, then O2 sensor sees the oxygen and thinks the mixture is lean. PCM adds more and more fuel to compensate (by means of increasing LONGFT), but O2 sensor still sees the oxygen. The PCM sets the lean code. Meantime, engine always runs rich, the spark plugs get brownish, the cat gets ruined prematurely. Sounds familiar? I didn't see it happened to Ranger, but my son's Suzuki and my neighbor's Hyundai both had cracks in exhaust manifold with these symptoms. Check the exhaust system between engine and first O2 for leaks. Do you hear or smell exhaust under hood with engine running? Sometimes the crack is hard to see without mirror and flashlight.
Also check the MAF sensor (near air filter), just to make sure it ain't got obstructer with dirt.
#16 Feb 1, 2010
No there are no exhaust leaks and no cracks. And I have already cleaned MAF with MAF sensor cleaner. Also i have put in a recent air filter about 5k ago.(I keep up maintenance on my truck, i have done everything, plugs, wires, oil every 3k with napa oil and napa filters, everything I buy is napa no junk parts, synthetic trans fluid, synthetic diff fluid, new brakes all around...you get the picture lol.) I scanned the truck with a biddies snap on scanner. I got a lot of stuff from it, but everything I wrote down is in my truck. Ill update you tomorrow probabley around 1230 afternoon.
#17 Feb 2, 2010
This is all the info I got from the scanner, none of this is in any order fyi, its just copied. Also some of this was with the truck running when the scanner asked for it to be and some was with just key on.
DPFE volts 1.38
Egrvr % 0 idle
SFTrim was moving between 6-10%
MAF (gm/s) 3.14
Fuelpw1 (ms) 5.5
IAT 22 degrees celcius
MAF volts .84
TP .88 volts
CaseGND .057-.099 volts
Hope this gives you the info you want.
Thanks A LOT!
#18 Feb 2, 2010
LFtrim is the injector pulse duty cycle (how long injector is open) correction. Default is 0%, 25% means it is 25% longer than on brand spanky new truck to get proper oxygen sensor reading.
LFtrim 25%- I can see that idle runs a little lean. But it's not too bad, my truck runs at ~22%. If you add LFtrim+SFTrim, it comes to 25%+10%=35%, which is close to failing limit of 40%, but it's not there yet.
This is at idle, RPMDES 723. You don't show 2500 rpm data. The manual says LFtrim+SFTrim drops more than 15% with throttle open half way, it indicates air leak.
If the tester got graphic feature, watch how fast SFTrim moves up and down to eliminate "slow oxygen sensor" syndrome. Watch MAF under different RMPs graph, to make sure the line is smooth and no sudden drops. What's the fuel pressure at the rail?
#19 Feb 2, 2010
This is how good MAF graph should look like.
#20 Feb 2, 2010
And this is O2 sensor graph charts.
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