Bad fuel injector?

Hello,
My '97 has the annoying "random misfire" error code. Engine misses at idle and at low RPMs, shaking a bit until RPMs go up past 1200.
I am going through the items suggested in other threads (checking ignition components, vac leaks, CPS, fuel pressure...).

Yesteday I started unplugging plug wires and injector wires. Neither in #1 did any difference to the engine. I pulled the (fairly new) plug and it looks OK. Could this be a sign of a bad injector?

Thanks.
Mikel

Could be the sign of a bad plug wire,,,,, or plug. swap to another hole and try again.
Both wires and plugs have been known to be bad out of the box.
Even the connection could be bad between the injector and plug....I,ve had that numerous times on my 96....

Could be a bad spark plug internally, bad spark HV wire, bad injector, or bad wire/connector to the injector, or a bad computer. Try a new spark plug first. Also check the rotor and cap, make sure the inside of the CAP is not shorted, or corroded, or damaged on #1, or just replace the rotor and cap if they old and worn.

HV spark wire should read about 1000 ohms per foot of length internal resistance, end to end (loose) (for most SP wires....), if it is 1 ohm or less, or infinite the wire is bad.

If the spark is good on number one, then beg or borrow a NOID light (or use a volt meter) and check the disconnected Fuel injector plug for a flashing noid light, or check for a ground pulse (IIRC) (open-short-open-short) on one wire with an ohm meter, It should read a steady 12 volts on the other wire to the battery ground (black probe connected the battery negative post), and the other connector should go from infinite resistance to a ground, short, about 1 ohm pulse to fire the injector.

Power off, FI #1 disconnected, you can use a 9 volt battery and jumper wires, mini clips, to test the FI, You should hear a click as the apply and remove power to the injector. NO click sound means it is dead. IF you pull the injector you should be able to blow air through it with the injector getting 9 V from the battery.

If all the parts are good, it is time to do a compression test on Cyl #1!!!!

Run the tank down to a quarter and add a can of quality injector cleaner to it. Once the tank is down to an eighth, add 5 gallons and do it again. Then add another can at the eigth tank and fill the tank.

If a particular cylinder misfires the PCM will identify it. You stated random misfire. At the age/mileage the Heep is at, dirty injectors are the norm as most folks do not run a fuel containing injector cleaners. One of the reasons I run premium is the for the injector additive. My Wife runs premium in her Full Size Bronco for that same reason plus the mileage went up enough to pay for the cost differential.

Plus, it helps my performance by a chunk...

The only injector cleaner I would run is BG44K. It is the closest thing to a tuneup in a can you will ever find.

^^Does work... I did the three can routine on the 98 when I first got it from the Dealer not quite two years ago. Was throwing a tone of dodes which they did not want to address. Made the purchase a bargain. After running the cleaner, the random misfire codes went away. NSS had to be cleaned, a lengthy list of petty problems that took all of a couple of hours to resolve.

just sayin...

I ran three bottles of injector cleaner and no noticeable improvement.:bawl: After I check compression and verify that #1 is getting spark -again-, I'm going to snatch some injectors from the junkyard and swap them. Thank you all.

Don't swap all the injectors, that just adds 5 new variables to the fun, LOL. Stay focused on the bad cylinder.

I take it two jumper wires and 9 volt battery was too hard to do?

Do you know how to use a volt / ohm meter? If not, get one and learn fast!!!

^^There it is. Swapping out suspect injectors for a complete set of..... suspect injectors.

Not exactly a good idea. FYI, a long bladed screwdriver placed pointy end on the injector and dull end in your ear will let you hear the injector fire.

New injectors are not all that pricey. You can get a rebuilt injector for around $40.00 including the core charge which get rebated when you send the old one back.

I think you guys are right. I pulled the plug to #1 injector and there was a noticeable difference driving. Since I didn't know if the computer was going into some sort of limp mode, I replugged it and I drove for a short distance with #1 plug wire disconnected. Again a noticeable difference.

I forgot to add that there is a rattle in the catalytic converter and that occasionally the exhaust smells rich. Could a bad cat have damaged the downstream o2 sensor? Mileage is 175K. Will continue checking the things suggested this weekend.

Thank you.

LOL, such a minor detail, just a little rattle, LOL.

You need a new Cat converter, problem(s) solved.

But a bad O2 sensor may have killed the Cat converter by running it rich, and burning up the Cat converter, which is probably why it is rattling now. So test the front O2 sensor and replace it if it is bad, before you burn up a new Cat.

I replaced the cat (old one was broken inside) and the two 02 sensors.

The miss is still there. I suppose these items needed to be replaced anyway. This weekend I'll start going through the other checks suggested...

By the way, I have found a loose connector, just dangling. Any idea where it's supposed to go??





Thanks.

One or more leaking fuel injectors would run it rich (in spite of a good O2 sensor), and eventually damage the Cat converter, and if the leak is bad enough it could wash oil off the cylinder and damage that cylinder, killing compression for good, and thus a miss!

A bad spark over time is nearly as bad, same effect!!!

Off the top of my head that looks like a plug for an AC component.

I haven't seen anyone ask this yet, I may have missed it, but what are the exact core numbers? Is it just P0300 or are there other codes that point to specific cylinders?

Talyn said:

Off the top of my head that looks like a plug for an AC component.

I haven't seen anyone ask this yet, I may have missed it, but what are the exact core numbers? Is it just P0300 or are there other codes that point to specific cylinders?

Click to expand...

I haven't been able to find any vacant connectors in the range of that cable...

It's been a while since I read the error codes, but it was a random misfire, followed by multiple misfires in cylinders. I'll check them again.

Thanks.

Mikel said:

I haven't been able to find any vacant connectors in the range of that cable...

It's been a while since I read the error codes, but it was a random misfire, followed by multiple misfires in cylinders. I'll check them again.

Thanks.

Click to expand...

One of two possibilities since I can't see all of that area of the engine bay in your picture. In my set up, one lead goes to the low pressure switch that sits on top of the AC accumulator, or it could be the power lead to the engine bay light mounted under the hood.....

That plug may be the underhood light.

Ahh. the underhood light.. I forgot about that since I unplug all of mine. That is probably what it is since it has that mounting lug.

More things I have checked:

- Fuel pressure is steady at 50PSI.
- Tried a set of junkyard injectors and it runs exactly the same. Cylinders 1 and 6 show no change in idle when the injectors are unplugged, just like before.
- Could not check compression because of the large relief in the head threads... The threads in my compression tester were not long enough. All plugs look the same, light greysh. My thinking is that if the compression in one cylinder is low enough to cause trouble, it would become apparent in the plugs. Am I wrong? I'll make an adapter of somer sort and try again.
- Plugs are new champions, all firing.

Thank you all.

Not all the time. You also may want to get a noid light and make sure each injector is getting a pulse. Or listen to each injector. You may want to pull the valve cover and check cam lift at those two cylinders.