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Diagnosing misfires...


johndoby

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My dad's ranger was in desperate need of a good tune-up, so I took on the task of getting it tip-top for him. First and probably most importantly, the truck has over 200k, so it's not very fresh to begin with.

The idle is hit or miss...sometimes it wants to idle ok, other times it acts like it wants to go dead. There's a slight hesitation once you begin feathering the gas and clutch, then the rpm's pick up and it does ok. Throughout the rpm range (although there is a sweet spot), the engine misses and surges very slightly. It's not bucking, mind you, just slight inconsistencies. Just like the idle, sometimes it is better, sometimes it is worse.

Here's what I've done -
Installed a new clutch kit (unrelated)
New plug wires
New plugs (gapped to .044" per manual)
New air filter
New fuel filter
New O2 sensor (pre-cat)
Cleaned MAF sensor
Cleaned Throttle-body/IAC motor

Doing all of this gave the motor a noticeable increase in power, but the miss is still there. I should mention that unplugging the MAF sensor during idle improves the idle significantly, but the miss is still there under acceleration and cruising (w/MAF disconnected). I'm not sure if this is a sign that my MAF is bad, but I sure wish there was a better way than spending $100 to find out. Unplugging the IAC at idle almost kills the engine, so unless it is just out of spec, I don't think it's the culprit. Could the TPS be causing this kind of behavior?

I really hope someone is not as stumped as I am at this point.

Thanks for reading!
 


SykoRanger88

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mine had similar problems and it ended up being the timing was off a little, also i heard engine grounds can cause this also, if the ground from the wiper motor to the back of the engine behind the intake is loose or something, im not sure if the TPS would cause all that hopefully some1 else has input.
 

Mark_88

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mine had similar problems and it ended up being the timing was off a little, also i heard engine grounds can cause this also, if the ground from the wiper motor to the back of the engine behind the intake is loose or something, im not sure if the TPS would cause all that hopefully some1 else has input.
Good that you got the timing right...:)

Johndoby: If the idle improves with the MAF disconnected then that may be your problem...did you modify the air intake at all? Slight changes to the airflow have caused miscues on the MAF...other than that...go to a junkyard and you can pick one up for next to nothing...may be that you are picking up someone elses' problem, so I usually get two just in case...unless you really want to spend that $100...
 

johndoby

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Good that you got the timing right...:)

Johndoby: If the idle improves with the MAF disconnected then that may be your problem...did you modify the air intake at all? Slight changes to the airflow have caused miscues on the MAF...other than that...go to a junkyard and you can pick one up for next to nothing...may be that you are picking up someone elses' problem, so I usually get two just in case...unless you really want to spend that $100...
I planned on calling the junkyard today...who knows with my local junkyard though, they charge ridiculous prices sometimes. Last visit, they charged me $30 for a plastic insert to go in a fog light hole.

Also, I'll do some research on checking and adjusting the timing. That's one area of auto repair I've never had personal experience with. If anyone has any tips for this particular engine that I might not read in a Haynes manual, please feel free to share.

Thanks,

John
 

Bryan22

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your timing won't be a little off. he has a distributor you have a distributorless system.you can not change spark timing, it's all computer controlled. if the valve timing was off it would run really really bad. that's probably not your problem. but checking the timing is pretty easy. pull the plug out of the timing belt cover so you can see the cam gear then turn the motor by hand until is on it's mark(visible through the hole) and the crank shaft pulleys mark is lined up with the TDC mark on the belt cover. if they are both on their marks then everything is good. :)
 
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johndoby

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That makes much more sense. I knew I had an electronic ignition/coil pack system and was wondering how in the world I would adjust the timing.

I also talked the guys at my local auto parts store into letting me install a MAF sensor before purchasing just to make sure that mine was indeed faulty. The new MAF had the same symptoms as my old one, so I don't believe it's the culprit. On a side note, I unplugged the TPS sensor, and although it didn't change the idle (it was doing ok at the moment), it seems like the engine ran smoother when I gave it a little gas. Normally revving just slightly would cause it to miss like crazy, but it was smooth as butter. I plugged it BACK in and nothing changed...still smooth.

The miss, however, is still there, with the diagnosis as elusive as ever.

I am running out of things to check. I guess the next stop would be the injection system.

Any more ideas?

I don't see why Im getting these issues without a check engine light. A code might be helpful at this point.
 

Mark_88

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Here is something that is inexpensive and may show you what the problem is...find a good dark spot (at night with little or no ambient light) and spray water onto the engine from a squirt bottle (you don't need much water) and watch for sparks...if your wires are arching out on something or you have any loose connections you should be able to see it at night...if you see sparks...check where it is coming from and replace the wires...or move them away from the metal...

I've only had to use this technique a few times and found some plug wires were arching on the valve cover...it takes quite a bit of power out of the engine and can cause rough idle...

But, then again, so can any number of things...like a plugged or non-functioning EGR...you can actually test the EGR valve with a vacuum tester to see if the diaphram is broken...I forget what else can go wrong with them other than getting plugged up with gunk...which is actually common on older engines...
 

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that's a good idea from mark. I would also take a multi-meter outside and check the resistance on the coil packs, just to make sure they are within spec.
 

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Another thing to do is when you clean your maf and do a major tune up you should disconnect your battery for about 10 minutes to kill the KAM (keep alive memory). This way the truck will start out with a fresh slate as it may have 'acquired' some bad habits from a dirty maf/ poor running engine.
 

johndoby

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Another thing to do is when you clean your maf and do a major tune up you should disconnect your battery for about 10 minutes to kill the KAM (keep alive memory). This way the truck will start out with a fresh slate as it may have 'acquired' some bad habits from a dirty maf/ poor running engine.
I thought about this too and disconnected the battery while I was performing the tune-up (over 3 hours), so it should have had a fresh start when I finished.

I also performed the "dark" test after installing the new plug wires. I haven't checked the resistance on the coil packs but I did check the spark on both banks by plugging a wire into an old plug and grounding it. I'll look into the procedure for checking resistance.

Thanks,

John
 

Kedyn's Crow

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I'm having a similar problem with my truck, it was just spitting and sputtering at certain rpms when it was cold, now it is doing it all the time. I have replaced the plugs and the wires. This happened to me last year and then it went away. I have a 1990 2.3 with the coil packs separate one on each side. If I unplug the electrical connection to the driver's side coil pack, the truck runs nice and smooth. I've checked the coil pack and it is fine and I have even swapped it from the passenger side to the driver side to make sure and it's still doing the same thing. I can't find any broke wires so could this be an issue with the ignition control module?
 

johndoby

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I did a little testing this afternoon and found something interesting. When I unplug the coil pack for the driver's side, the engine runs slightly worse but not much. When I unplug the driver's side, it runs like $h!t. I tried unplugging one wire at a time on the drivers side coil pack to see if I could narrow it down. On two of the plugs, the spark arched like crazy from almost one inch away and was very visible and audible. The other two, for cylinder 1 & 3, were barely arching at all, and had to be within 1/4-3/8" away from coil pack to even arch. What is more interesting is that when I changed the plugs, the ones for cylinders 1 & 3 on the driver's side looked almost brand new (after 70,000 miles), while the others were fairly worn. I'm thinking the coil pack might be bad. Does this sound symptomatic? I'm thinking the problem might have been there for longer than I thought and that my dad just didnt notice it, or passed it off as being normal behavior for an engine with that many miles.

Thanks,
John
 

LivinTheDream

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I have the same problem. I have a 96 Ranger. It idles fine but then only while driving does it sputter and buck. But let me describe it better. The engine does not just lose power, it bucks hard. It feels like a kill witch is being turned on and off. Then when you let your foot off the gas and back on… the problem is solved until anther minute or so. Sometimes it drives fine for 20 minutes with out bucking. Other times it bucks in every gear.

I don't know where to start.

Also the engine light flickers when it bucks but never holds a code. The light just flickers when it bucks.
 

Mark_88

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I have the same problem. I have a 96 Ranger. It idles fine but then only while driving does it sputter and buck. But let me describe it better. The engine does not just lose power, it bucks hard. It feels like a kill witch is being turned on and off. Then when you let your foot off the gas and back on… the problem is solved until anther minute or so. Sometimes it drives fine for 20 minutes with out bucking. Other times it bucks in every gear.

I don't know where to start.

Also the engine light flickers when it bucks but never holds a code. The light just flickers when it bucks.
This may or may not be related, but my Tempo used to buck (bunny hop, actually) down the highway sporadicly (meaning it didn't happen all the time and was hard to diagnose)...but that issue turned out to be the in-tank fuel pump...that I had to replace three times over 14 years...
 

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