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Help With A Misfire Problem?


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Can anyone help? I have a 2003 Mercury Sable. Yesterday the engine began running very rough and the check engine light began flashing. I had a shop read the OBD II codes, and got 3 different ones, P0301, P0316, and P0351. I've done some reading and from what I've been able to understand, if it is a coil problem, then more than 1 cylinder would have a misfire since the coil runs 2 spark plugs. The plugs and wires are less than a year old, I replaced them about 8 months ago. I also had the injectors cleaned about the same time. What should I look at as the most likely culprit?

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Can anyone help? I have a 2003 Mercury Sable. Yesterday the engine began running very rough and the check engine light began flashing. I had a shop read the OBD II codes, and got 3 different ones, P0301, P0316, and P0351. I've done some reading and from what I've been able to understand, if it is a coil problem, then more than 1 cylinder would have a misfire since the coil runs 2 spark plugs. The plugs and wires are less than a year old, I replaced them about 8 months ago. I also had the injectors cleaned about the same time. What should I look at as the most likely culprit?

0351 is a coil primary fault so that is where to start.

"P0351 Ignition Coil A Primary circuit fault"

If it is a Vulcan, coil is on the front, easy to change.

-chart-

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Replace the coil for #1 cylinder. Examine/replace the boot from the coil to the plug. Should clear all 3 codes.

This is DOHC, correct?

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Replace the coil for #1 cylinder. Examine/replace the boot from the coil to the plug. Should clear all 3 codes.

This is DOHC, correct?

Either engine same coil pack. Just the location is different.

With a fault in the primary, it is either the coil or the primary plug to the coilpack.

-chart-

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Tested the coil pack and found a bad tower to the #1 cylinder. Replaced the coil pack, disconnected the battery for a few minutes to reset the check engine light, and all is well. Thanks for your help guys, we're all done here.

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Tested the coil pack and found a bad tower to the #1 cylinder. Replaced the coil pack, disconnected the battery for a few minutes to reset the check engine light, and all is well. Thanks for your help guys, we're all done here.

Congrats and you saved yourself a bundle of $$$.

Now send us a pic of your SABLE.

-chart-

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  • 3 months later...

Has any one had a bad fuel injector trigger the CEL with a lean code?

It is possible. Is it just a single bank lean code or both banks? If its both banks then it probably isn't an injector issue. There is a SUPER RARE chance that an injector on each bank was clogged, but the motor would be running terribly and you would have a misfire on a single cylinder on both banks.

I'm guessing you have a misfire code? What cylinder is misfiring and what's the lean code bank 1 (P0171) or 2(P0174)? List any and ALL codes here please.

Edited by breeves002
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Has any one had a bad fuel injector trigger the CEL with a lean code?

You would need a misfire code and a lean code on one bank to suggest that.

A ign misfire can come up as lean also. First thought is the opposite, but the O2 sensor measures Oxy and only Oxy.

Misfire lets O2 and unbuened fuel out and the sensor only sees the O2 and does not care about the unbuened fuel. That fuel will burn in the cat.

-chart-

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I'm getting an 071,lean bank one for the most part...although I've also had an 074,lean both banks,as well as misfire within the first 100 rpm (don't remember the code).I've replaced the coil,wires,DPFE,plugs,O ring on the air valve on the right rear of the intake manifold,air fiter,fuel filter,cleaned the MAF sensor...looked for any signs of a vacuum leak and have'nt found anything beyond a suspiciously sluggish fuel injector at #1 clyinder.There is no visible schrader valve on the fuel rail,so I don't know for sure about the fuel pump pressure yet.I can reset the CEL to go off after reading the codes,but it comes back on after 10-15 miles driving.I have anew fuel injector on order from Rock Auto,and wonder if it can be replaced w/o removing the plenum or not.I don't think the O2 sensors are at fault,aas they show voltage readings within parameters (0.65v).W/O a heated garage here in NY,this s**t has gotten old fast...

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I'm getting an 071,lean bank one for the most part...although I've also had an 074,lean both banks,as well as misfire within the first 100 rpm (don't remember the code).I've replaced the coil,wires,DPFE,plugs,O ring on the air valve on the right rear of the intake manifold,air fiter,fuel filter,cleaned the MAF sensor...looked for any signs of a vacuum leak and have'nt found anything beyond a suspiciously sluggish fuel injector at #1 clyinder.There is no visible schrader valve on the fuel rail,so I don't know for sure about the fuel pump pressure yet.I can reset the CEL to go off after reading the codes,but it comes back on after 10-15 miles driving.I have anew fuel injector on order from Rock Auto,and wonder if it can be replaced w/o removing the plenum or not.I don't think the O2 sensors are at fault,aas they show voltage readings within parameters (0.65v).W/O a heated garage here in NY,this s**t has gotten old fast...

By your year, I think they did not use a shrader valve on the fuel rail. Pressure transducer there instead and it manages the fuel pressure by adjusting the voltage to the fuel pump. A lean code means the system can't adjust the fuel trims enough to get rid of O2 in the first O2 sensor. Likely then not enough fuel to the fuel rail.

Did you replace the fuel filte?

-chart-

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gas mileage is around 10 mpg according to the computer.i it can be believed....it seems to be improving from 8.5 with some Seafoam...This sure points to a bad MAF sensor w/o my checking it with a VOM (I've cleaned it twice with sensor cleaner)...but the exhaust does not smell foul.Of course that could be the cats doing their job,but they don't seem to be overheated as would be the case with a rich mixture.That 071/1074 code puzzles he s**t outa me..then the poor gas mileage?...GREMLINS ...

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Sounds like a vacuum leak to me! Do you have hard gear shifts? If not then I doubt it's the maf sensor. Check/replace PCV valve, elbow, and hose. Grab a cigar and blow the smoke into the brake booster. Look for where it comes out. Really sounds like a vacuum leak though.

You need a scan tool that supports fuel pressure to get the actual pressure. Could be causing lean codes, would more likely cause a P0300 random miss. Do you have low power? When you go WOT do you have a lot less power than normal? They got rid of the valve on the rail mid 03.

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gas mileage is around 10 mpg according to the computer.i it can be believed....it seems to be improving from 8.5 with some Seafoam...This sure points to a bad MAF sensor w/o my checking it with a VOM (I've cleaned it twice with sensor cleaner)...but the exhaust does not smell foul.Of course that could be the cats doing their job,but they don't seem to be overheated as would be the case with a rich mixture.That 071/1074 code puzzles he s**t outa me..then the poor gas mileage?...GREMLINS ...

You have sysmptoms of low fuel pressure. The system has short term and long term trims to get the 02 balanced. Short term can go ~+45% and long term can go ~+35%. If it senses lean it keeps adding trim (time the injectors are open on each firing) to try to get enough fuel to match the air.

MPG calculations are done by doing a math program on how many cycles the injectors see (rev of the engine) and how long they are open in toal. (simplifed explaining) If your fuel p is low, injectors are open much more time than normal to get the fuel, but it makes large errors in the MPG calculations. It is telling a lie.

Low fuel P can be caused by the pump, pump driver module, or the pressure sensor.

And for what it is worth, the system treats the engine as 2 engines, 3 cyl bank each and runs them separate. So you have trims on bank 1 and trims on bank 2 and) O2 sensor on each bank to control that bank.

-chart-

Edited by -chart-
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You have sysmptoms of low fuel pressure. The system has short term and long term trims to get the 02 balanced. Short term can go ~+45% and long term can go ~+35%. If it senses lean it keeps adding trim (time the injectors are open on each firing) to try to get enough fuel to match the air.

MPG calculations are done by doing a math program on how many cycles the injectors see (rev of the engine) and how long they are open in toal. (simplifed explaining) If your fuel p is low, injectors are open much more time than normal to get the fuel, but it makes large errors in the MPG calculations. It is telling a lie.

Low fuel P can be caused by the pump, pump driver module, or the pressure sensor.

And for what it is worth, the system treats the engine as 2 engines, 3 cyl bank each and runs them separate. So you have trims on bank 1 and trims on bank 2 and) O2 sensor on each bank to control that bank.

-chart-

I've been using an Actron scan tool to try and identify the problem.The fuel rail pressure reads 2.80 KPA ( I don't understand this interms of psi),so I'm not sure in I have a problem with the fuel pump in the tank or the fuel pressure transducer...however as my wife has often driven until the 'low fuel' warning light comes on,I would not be surprised to find the pump is bad.I don't know how to determine fuel pressure with this car ( '04 Taurus OHV V-6,3.0L).Fuel level input pressure shows a reading of 97.6%...so perhaps (hopefully) the pump is good,and the transducer is at fault.How do you check the transducer?... my Chilton's is real spotty,not even picturing it in my 1996-05 repair manual (26702)...Your help is GREATLY appreciated! Thanks,Gary

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I've been using an Actron scan tool to try and identify the problem.The fuel rail pressure reads 2.80 KPA ( I don't understand this interms of psi),so I'm not sure in I have a problem with the fuel pump in the tank or the fuel pressure transducer...however as my wife has often driven until the 'low fuel' warning light comes on,I would not be surprised to find the pump is bad.I don't know how to determine fuel pressure with this car ( '04 Taurus OHV V-6,3.0L).Fuel level input pressure shows a reading of 97.6%...so perhaps (hopefully) the pump is good,and the transducer is at fault.How do you check the transducer?... my Chilton's is real spotty,not even picturing it in my 1996-05 repair manual (26702)...Your help is GREATLY appreciated! Thanks,Gary

To convert pounds per square inch to kilopascals(PSI to KPA), multiply the PSI value by 6.894757293168361.

To convert kilopascals to pounds per square inch(KPA to PSI), multiply the kpa value by .14503773773020923.

Does not compute. Fuel rail pressure should be ~38-40 PSI.

-chart-

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To convert pounds per square inch to kilopascals(PSI to KPA), multiply the PSI value by 6.894757293168361.

To convert kilopascals to pounds per square inch(KPA to PSI), multiply the kpa value by .14503773773020923.

Does not compute. Fuel rail pressure should be ~38-40 PSI.

-chart-

OK,if I'm correct here,then 2.8KPA would equal about 0.395 psi,yes?...Something is screwy here.The car is drivable with a noticeable miss ,but only showing a PO171 (lean bank 1) code....

Edited by GSD
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I'm sure it was 280kpa which equals ~40PSI. If you had 0.4PSI the car would not be running. Check the fuel trims with your scan tool. Compare LTFT on bank one to the LTFT on bank two. Since you are only getting a bank one code, then in theory the bank 1 trims should be +25% or higher. If the bank two isn't near that (normal range of +5% to -5%) then we know it's ONLY a bank one issue. If it's still high, lets say between +15 to +20% then we could assume vacuum leak.

For what it's worth, read this guide that I wrote (with help from other people like Nick): http://www.taurusclu...e-misfires.html

Check the simple things first (like coil pack for cracks). Check for a strong spark, etc. Since the misfiring cylinder just dumps fuel, the O2 sensors see extra O2 then richen the mixture. Still see extra O2 so it keeps slowly getting richer until the code sets. Chart explained that earlier. Possibly fixing the misfire will fix the system too lean code. Could be the other way around though.

Just read the guide, and do the easy stuff first. Cracks on the underside of the coil pack cause misfires often.

Edited by breeves002
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Hey,Breeves002...thanks very much for your helpful thoughts,As mentioned,I replaced w/ new coilpack,Autolite wires & 104 plugs,cleaned the MAF sensor,replaced the DPFE sensor,the O-ring on the manifold back runner valve,checked the PCV'S and all vacuum lines for leaks ( and found none)...and only found the # 1 cylinder fuel injector showing some strange behaviors.In changing out the O2 sensor upstream of bank 1,I found it to be sooty...so I changed it out too.The problem still continued...so we took off the the Ford dealer,who only found the fuel injector problem,as I did.A local shop did not want to get into it,claiming that the intake plenum bolts tend to snap off...So the Ford dealer (who did'nt stock the f/i ) is going to change it out to the tune of $500 and change,minus the $100 dx fee.Were it not so damned cold and stormy,I was considering doing the job myself,but it's been 2+ weeks up and under this rig,and the wife wants the car....and the dealer can now give it a shot.Fuel injector cleaner (Seafoam,Lucas,and Techron used in three different fill ups seemed to be helping).

The new fuel injector from Rock Auto was $20,but still has'nt arrived....the car is promised for Monday..

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Hey,Breeves002...thanks very much for your helpful thoughts,As mentioned,I replaced w/ new coilpack,Autolite wires & 104 plugs,cleaned the MAF sensor,replaced the DPFE sensor,the O-ring on the manifold back runner valve,checked the PCV'S and all vacuum lines for leaks ( and found none)...and only found the # 1 cylinder fuel injector showing some strange behaviors.In changing out the O2 sensor upstream of bank 1,I found it to be sooty...so I changed it out too.The problem still continued...so we took off the the Ford dealer,who only found the fuel injector problem,as I did.A local shop did not want to get into it,claiming that the intake plenum bolts tend to snap off...So the Ford dealer (who did'nt stock the f/i ) is going to change it out to the tune of $500 and change,minus the $100 dx fee.Were it not so damned cold and stormy,I was considering doing the job myself,but it's been 2+ weeks up and under this rig,and the wife wants the car....and the dealer can now give it a shot.Fuel injector cleaner (Seafoam,Lucas,and Techron used in three different fill ups seemed to be helping).

The new fuel injector from Rock Auto was $20,but still has'nt arrived....the car is promised for Monday..

Injector problems are not really common. Anything mechanical can fail, as well as many non mechanical.

Not the first thing one would expect. A failing injector can give too much gas or too little gas. In either case, the PCM with the input from the O2 sensor will adjust the good cylinders out of range. I have only had 1 on 7 Taurus/Sables and then on '88 and it leaked down causing one cylinder to act flooded on startup but run fine after it started firing. Slow leakdown when engine was off.

Good Luck.

-chart-

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I agree with chart. Injector problems are rare, but do exist. Could be the O-Ring on the injector?? Oil on the plug?

Switching an injector isn't bad, just can't be done in the rain. Remove upper intake, remove fuel rail and replace the injector.

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