Cylinder 1 misfire, spark looks fine

[MorseM]

Hi all, I have a 1996 Aerostar w/ a 4.0 engine (170,000 miles on engine, new spark plugs, distributer cap, wires, rotor within 10,000 miles) that is running rough and showing "Check Engine". The fault codes are "P0301 Cylinder 1 Misfire Detection" and "P0171 System too Lean (Bank 1)". I changed one of the oxygen sensors (the one just after the catalytic converter) several hundred miles age but the fault light returned almost immediately. I took the spark plug out of the # 1 cylinder (passenger side, closest to radiator) and laid it against frame, turned starter; nice blue spark. How do I diagnose the problem? MorseM w/ a good ol' Aerostar

[96_4wdr]

welcome morseM,


simple things first.
it's either spark or fuel.
since you've confirmed you've got spark to #1, then suspect fuel.

how do all the plugs look? same color?

when was the MAF last cleaned/replaced? search forum threads for directions how to remove the MAF element and soak in carb. cleaner

2nd CAT sensor located after the CAT is only a monitor on 1st sensor and CAT correct operation, has nothing to do with correct fuel mix. replace first CAT sensor, they only last 50k>100k miles and usually die slowly affecting fuel mix and operation.

after these simple fixes, switch injectors between #1 cyl and another. does problem follow injector?

glad you're aboard.

i had the same problem with my 96 4L AWD last year, defective new spark plug ign wires. replaced with Motorcraft.
best source, our site sponsor RockAuto

use ONLY Motorcraft or Autolite plugs and wires in these 4L EDIS Aeros. the high eng. comp temps and high spark voltages destroy other wire sets
use lots of silicone dielectric grease in the spark p. wire connectors, both ends

[93nighthawk]

Welcome MorseM!

Originally Posted by MorseM

Hi all,
I have a 1996 Aerostar w/ a 4.0 engine (170,000 miles on engine, new spark plugs, distributer cap, wires, rotor within 10,000 miles)

Um, last time I checked, the 4.0L did not have a Dist Cap or rotor. Are you sure you don't have a 3.0L?

running rough and showing "Check Engine". The fault codes are "P0301 Cylinder 1 Misfire Detection" and "P0171 System too Lean (Bank 1)". I changed one of the oxygen sensors (the one just after the catalytic converter) several hundred miles age but the fault light returned almost immediately.

How do I diagnose the problem?
MorseM w/ a good ol' Aerostar

Like XLT said, you replaced the wrong O2 sensor. You need to replace the one before the cat. Cleaning the maf will help too. You might also want to check your vacuum lines. One might have slipped off when you did plugs/or on its own accord. This would also cause a lean condition.

Keep us up to date.

[MorseM]

Thank you both for the sound advice;
96_4wdr:
-The spark plugs were all of uniform color when I changed them and the wires seemed ok, they both had about 70,000 miles on them. I bought them at the local discount auto parts chain store. After I got the codes read this past week, I pulled # 1 spark plug and it smelled of fuel.
-I have never cleaned the MAF; but after your comments, I think I will be doing that this week!
-I will also change the front oxygen sensor. Is it ok to buy these at the discount chain? The ones they sell are Bosch.

93nighthawk:
-My mistake; no distributer cap, no rotor; it is a 4.0. I have several older cars to keep running for/with our children and got confused on what was done to what car.
-When I change the front Oxygen sensor I will look for open vacuum lines.

Thanks again for your responses and expertise, I will start back on it tomorrow and let you know how it goes.

[Bear River]

Upper intake manifold leaks are a fairly common problem. However they most often result in lean codes, stumbling or pinging, and not misfires. The problem is most likely either a problem in the ignition system or a fuel delivery problem. The cam position sensor can also be involved however. I have seen a bad sensor result in misfires or misfire codes.

[96_4wdr]

i believe Bosch builds FoMoCo's OEM O2 sensors, i've had good luck with them

i second the vacuum line failure/problem check. 13 year old rig and the heat/temps under the Aero hood guarentee vac. line failure. replaced all of mine several years ago

these 4L Aeros with OBDII systems display all types of strange symptoms with a 1 cylinder miss; Overdrive lockout, no torque converter lockup, shift problems. the van weight accentuate the symptoms
the HAL computer goes crazy trying to control all.

did the miss/problem show up after new plugs/wires?
what brand of plugs?

[Aeroman59]

Although you can put any plugs you like in an Aero , THEY WONT LAST as long as Motorcraft! in some cases less than 50% . I would swap to Motorcraft or Autolites first, lets go from there.
Speaking from the experiance I've had with my 3L when I've had any misfire (which is 3 times in 300,000 plus Kms) it's always been traced to plugs as the cause, in one case I had one come loose, this caused a month of headache until I finally took a wrench to it, a 1/8 turn extra fixed that problem. Bosch O2 sensors are fine. They are good for about 100K. A faulty front o2 sensor could easily cause the PO171 code, as well as a vac leak. I've had no problem with my injectors yet. You might find you have two seperate problems here.
Good luck,
Aeroman..

[Pablo-UA]

EEC computer has MOSFETs inside to actuate injectors w/o current contror witroll, so bad injector wiring ore bad inj. coil cause no codes, exept of P0301, so step #1 is to check pulses on injector with o-scope and if pulses are OK, check injector impedance, If you see elkectrically injector is OK may be mechanicalli it is bad ore clogged. Well, try comoression test too.