Yesterday my '99 Ranger (148K miles) began to misfire. Got home from work and put the scanner on it and retrieved an 0302 code. Reset the code and removed the spark plug from cyl #2 and replaced it wit a new one. No luck, engine still mifires. Removed the coil pack and perfrormed quick bench test; coil primaries measured .7 ohms and coil secondaries measured between 13K to 14K ohms across pairs. Compression checked cyl #2 and read 120 compared to 115 in #1. Reinstalled the coil pack and substituted #1 wire for the #2 wire to check if there was a bad plug wire on #2. No change, still misfired on cyl #2. Returned wires to original position. Got out the timing light and connected it to the #2 cylinder just to see if it would activate. The timing light triggered off #2 so I assume that there is high voltage getting to #2 plug. Looks like there may be three possibilities; bad cam position sensor, bad coil pack, bad PCM. Chose the lesser $ impact of the three and bought a new CMP. You guessed it NO LUCK. Need some serious suggestions here!!!! I'm totally frustrated. Could the coil pack be defective even though it appears to be putting out voltage? Without causing damage can I safely pull the plug from #2 connect the plug wire to it and lay it next the the block to see if it fires with the engine running? Any troubleshooting suggestions?

 

Give it a shot, you won't do any damage.

If it were a bad coil then you would expect #6 cylinder to be misfiring as well, since the EDIS ignition system in your Ranger is a "waste spark" type which means it fires two plugs simultaneously. However, if there is a crack or other imperfection in the coilpack itself I suppose a single cylinder misfire could result from that.

What did the old plug look like? Is the #2 cylinder getting enough fuel? Maybe the fuel injector is going bonkers or something like that...

I doubt it's the PCM. I would be more inclined to think it's a base engine concern (i.e., bad valve) than I would the PCM going bad.

 

Rockledge, thanks for the feedback. I guess I got tunnel vision thinking about the misfire indication being a totally electric problem. Yesterday I found a extremely understanding and helpful mechanic and we spent a few minutes discussing the problem. Based on the tests that I had already performed his first thought was, fuel problem. He didn't have the time to spend on my truck but he let me use his EFI Quick Probe and Noid lights. I was able to perform a check of the EFI system in the parking lot of his business. The quick probe indicated that the #2 injector wasn't operating. Installed the Noid light on #2 injector connector and got a good indication, fuel control circuit was functioning properly, however the injector was not. Off to the local parts stores to get a fuel injector and new "O" rings. As luck would have it, none of independant auto parts stores or larger national chain parts stores in my town stock fuel injectors; they're special order items only. So now I have to wait a few days before I can complete the fix.

After seeing how the Quick Probe and Noid lights helped with the trouleshooting, I can see the need for adding them to my collection in the very near future. Heck Christmas is just around the corner!! Wanted to let others know that there are inexpensive diagnostic tools out there that make the process MUCH simplier.

 

New fuel injector arrived in a few days and I finally completed the repair. I've been driving the truck for about a week and the engine misfire is a thing of the past. Now another issue has come up!! When coming to a stop the engine RPM drops off and it begins to stall. It doesn't do this all the time just enough to be a painin the butt. A quick stab on the gas gets it back on line.

During the replacement of the #2 injector I removed the other injectors on the fuel rail to take a look at them. Very surprised when I discovered that the plastic hat on all three injectors was cracked. The crack(s) run from the outer edge of the "flat" all the way to the injector tip at the center. Not sure if this happened during disassembly or whether the plastic has become brittle over time and has cracked on its own. I didn't have the correct tool to disconnect the fuel line from the rail so I did have some difficulty in getting enough clearance to remove the injectors from the rail. Wonder if I tweaked the injectors and caused the cracks?

The motor is flexi fuel rated and I have been using E85 quite a bit; I wonder if there has been some degredation to the plastic due to the fuel? Has anyone else seen same issue with cracked injector hats? Wonder if the cracks are affecting fuel flow at low speed? Could these cracks be the cause of the idle drop off? Has anyone out there seen similar problem? Just when you think all is well!!!!

 

I wish I had read your thread earlier I would have suggested the injector as well. I had the exact problems you are describing and pulled a misfire code on #6. After checking everything someone on the forum suggested the injector could be the problem. Replaced it and it was fine.

I did not notice any unusual cracking or wear on the other injectors, though.

Now, I too am having the idle problem. At first it just did it a couple times now this week it has started doing it almost constantly. Idles fine then drops down to below 500 rpm and sometimes low enough the engine stalls. My check engine light just came on so this weekend I will check out the problem. Some of the suggestions I've read in the archives include: check for vacuum leaks, dirty throttle body, defective EGR valve or dirty MAF sensor. I haven't looked at my repair manual yet and can't remember what solenoids are on the engine like an idle stop solenoid which I guess could be a problem as well. Guess I'll find out this weekend and if I find anything will let you know.

 

Thanks for the suggestions. When I get some "free" time at the end of next week I'll take a look at the areas you suggested. It just seems like too much of a coincidence that this low idle problem happened at the same time we completed the repair. My initial thoughts were that I left something disconnected. Double and triple checked things and didn't see anything disconnected or any thing that appeared to be partially attached or loose.

The stalling due to low idle has decreased some. I'm wondering if the fuel management portion of PCM was affected during the misfire events and the computer sensed and "learned" the bad conditions? Maybe over a period of time it will re-learn the good conditions and return to normal operation?

 

I had the same problem on my 98 f150 with 4.2 v6 (regarding throttle changes) after looking around, I replaced the pcm vac hoses, in particular the one just below the throttle control/air. there is a plastic tube that wore a hole in the hose which caused a vac. leak in the elbow. I went ahead and replaced all the hose and pcm for under 20bucks. I also have the other prob now and after completely checking spark, was making sure I was right about the injector being the culprit. How did you narrow down which injector was causing the problem? I have considered pulling them all and just getting all new for under $200. Thanks

 

I used a fuel injector tester made by Waekon to figure out which injector was bad. The probe of the tester is placed directly against the body of a fuel injector and it detects the mechanical impulses during the opening and closing of the solenoid in the injector. The tool will blink if the injector is working properly. If you find an injector that does not flash the light in the tester it could either be that injector is bad or that there is no signal from the PCM to pulse the injector. That's where the Noid light comes in. Disconnect the electrical connector from the injector and connect a Noid light into the plug on the fuel harness and start the truck. If the light blinks then there is electrical signal present and the problem is a bad injector. Good Luck!!

Here's the info on where I bought the fuel injector tester and the Noid Light kit: Waekon 76400 - Electronic Fuel Injection Quick Probe
OTC 3050C - 8 Pc. Noid Light Test Kit with Extension Harness

 

I am doing a head gasket job and removed my fuel injectors along the way to find out one of them is cracked just as you described! the tip tip seems ok and in tact but there is a fat crack from the part that holds back to o-ring down the side. definitely worried about it breaking off more ore messing up the fuel spray pattern, really dont want to have to have to order a new one!