2.5L ('98-'01) Misfire Issues

[RonD]

Well, fuel pressure can drop to almost nothing with key off, it shouldn't but doesn't mean fuel pump is shot
Cycle key on and off a few times then retest, you should get/add about 10psi of pressure with each key on/off cycle
But yes does read like pressure may be low, fuel pressure gauge is about $25-$30, or can be rented as a kit for maybe $10?

 

[Shran]

I recently had a 1998 similar to yours, 2.5 2wd 5 speed. Had the typical bad fuel pump symptoms - would maybe idle sometimes, backfired, very low fuel pressure. Replaced the pump and it ran great for a couple days and started doing the same thing again.

As it turned out, the tank was full of very fine sediment that made its way through the strainer. It was pretty obvious when I pulled it apart the second time and examined things closer... I just missed it the first time.

Make sure you clean out your gas tank when you replace your pump, which it sounds like you'll probably be doing.

 

[americanclassic16]

I recently had a 1998 similar to yours, 2.5 2wd 5 speed. Had the typical bad fuel pump symptoms - would maybe idle sometimes, backfired, very low fuel pressure. Replaced the pump and it ran great for a couple days and started doing the same thing again.

As it turned out, the tank was full of very fine sediment that made its way through the strainer. It was pretty obvious when I pulled it apart the second time and examined things closer... I just missed it the first time.

Make sure you clean out your gas tank when you replace your pump, which it sounds like you'll probably be doing.

Thanks for the tip! I'll definitely take a look at that when I'm replacing the fuel pump. I don't want to do this again in two years...

 

[americanclassic16]

Well, good thing I checked the fuel pressure with a gauge because after testing, it looks fine. 60 psi at all times. I even got it running rough again, shut it off, put the fuel gauge on quickly and still got 60psi fuel pressure over a range of RPMs so it is definitely not the issue. Now that compression, spark, and fuel pressure have been ruled out, what's left? Injectors I guess, maybe some sensors? The misfire seems to be very dependent on particular conditions. Warm idle and the bottom of fourth gear are where it is most pronounced, it's not really noticeable during strong acceleration and right after a cold start. I'm still thinking TPS might be to blame (though the TPS data doesn't prove anything except my cable is stretched) but what other sensors could cause this issue? One thing I also noticed while driving is that when I was going up a hill, it was very sluggish/no power even with the pedal to the floor. Once I got to a certain point on the hill, it's like some switch suddenly flipped and it gained back the power and ran fine again until I got over the hill and into some lower RPMs. I'm starting to paint myself into a corner here, any suggestions of what to try next are appreciated.

 

[RonD]

Did you try running the engine with one coil pack disconnected?
I forget

If not do that to test if both coil packs are firing on all cylinders, dual spark plugs are just for more power so engine should run OK with either coil pack unplugged, just less power

 

[americanclassic16]

I just came back from one last test which might have yielded some good news (in a sense). I wanted to check the fuel injectors and remembered the test where you take a long screwdriver (in this case, I had a 26" arrow) and press it up against each injector to listen for a consistent clicking sound. I listened to the injectors on 1 and 2 and got a consistent click but when I tried 3, I heard nothing. I also heard consistent clicking on 4 and tried this many times over and every time it was the same: clicking on 1, 2, and 4; nothing on 3. I unplugged the spark plug wires for cylinder 3 from the coil packs and I didn't notice a change in how it ran but then did the same with another cylinder (1, in this case after plugging 3 back in) and also didn't notice much of a difference (but it's obviously already misfiring so it's hard to tell). Still, I'm inclined to believe that injector #3 is toast. What's another good test to ensure that injector is indeed dead? Keep in mind, it's located in the intake manifold "prison" so it's not that accessible but since injectors are kind of spendy and not super easy to replace on this engine, I'd like to make sure it's the problem before I go any further even though I'm reasonably certain that it is.

Also, with regards to the coil pack test, I did try that again after replacing the coil packs and the engine ran the same no matter which coil pack was plugged in. That also happens to back up the injector theory which is my leading suspect at this point.

 

[RonD]

No, there is not much more you can do to test injectors

You can disable both coil packs and crank the engine, then look at spark plug tips on say #2 and #3 to see if they both have same "wettness" but its a judgement call

There is always some air/fuel mix left in lower intake so if #3 injector was not working normally you may get what you have, misfire under load at certain times
Computer also has the option of running batch fire, with a 4cyl that means it would open 2 injectors at the same time to keep lower intake full of air/fuel mix, one step up from carb, lol

Once they are out you can test OHMs on each injector, 11-18ohms would be expected
And you could then use a Noid Light on wiring harness for #3 injector and crank engine to make sure #3 is getting grounded by computer, Noid light flashes

 

[americanclassic16]

I'll probably go ahead and replace the injector then and do those tests once I get it out to make sure it's not the harness and really is the injector. I'm reasonably certain this is the problem at this point and I definitely can't go any further without investigating this fully. I'll let you guys know what happens.

 

[americanclassic16]

Hello everyone!
I'm glad to report I can finally bring this thread to a victorious conclusion! The new injector has fixed the misfire at all rpm levels and it has helped significantly with the hesitation. Thanks to everybody who helped out and contributed to getting my ranger back on the road!

For those of you reading this down the line trying to fix problems of your own, here's a summary of the thread:
Initial problem: truck started misfiring heavily, blinking CEL, codes for random, 1st, and 2nd cylinder misfires.
First fix: used dual coil pack test to determine spark was an issue, replaced plugs and wires, no change
Second fix: replaced coil packs, passed dual coil pack test (after it failed with the original coil packs), still misfired, wouldn't set a code though
Third fix: Checked fuel pressure, passed, listened for clicking of each injector, injector #3 made no sound. Replaced injector #3, misfire resolved.

As you can probably see, the initial symptoms and codes weren't exactly indicative of a fuel injector issue (let alone on cylinder #3) but this presents the perfect opportunity to give my two cents on using forums to your best advantage. You're probably looking around for a thread that discusses the exact issue that is present on your vehicle and gives the exact fix that will get it back on the road. If you can find it, good for you, but you're likely to eventually find a bunch of threads that provide information relevant to your issue but don't seem to provide a common solution. The best strategy is to learn the methods of diagnosis presented in these threads that will allow you to isolate and find/rule out each individual possibility. A methodical approach starting with the most likely/cheapest issue usually leads to the best resolution in my experience. Even though it may be time consuming and you're often times wrong, each test and the experience that comes with it is still just as valuable whether it works or not. So the next time your vehicle breaks down (and it will), look at it as a learning experience! With the experience that comes with each fix, it just gets easier!

Thanks and good luck!

-Americanclassic16

 

[RonD]

Good work

Thanks for the update and THE FIX