'98 Ram injector ghosts----UPDATE

[kenz]

A friend came to me today with a problem on his son's truck. '98 Ram 1500 4x4 with 360 motor 90,xxx miles. I'll try to remember what he told me. Was driving along fine and the motor just dropped into a rough run situation, sputtering like it wanted to die. Code checked said #1 and #2 injector bad/missfire. Replaced #1 injector and ran a little better. Replaced #2 and ran worse than before. He has done a complete tuneup, plugs, wires, etc. Replaced the crank sensor, and I believe the cam sensor. Still runs rough, worse on idle. Still says #1 and #2 bad. Swapped #1 with #3 and still gives #1 bad.  Has check fuel pressure and it is good. Checked injector wiring and also looks good. He had mentioned that he put a scan tool (what it was I don't know) that showed that the injectors were working, tool shows flashing light when injector fires. I mentioned checking all the grounds, and possibly injector wiring with a meter. The difficult part is that Dad is here in Michigan and son is in Tennessee. Although he is working, he can't afford a trip to the dealer, but can't keep throwing parts at it either. So I'm wondering if anyone had any ideas I could pass along.

[Kilch123]

To check injectors:

To test the injector only, disconnect the fuel injector wire harness connector from the injector. Place an ohmmeter across the injector terminals. Resistance reading should be approximately 12 ohms +/- 1.2 ohms at 20°C (68°F) .

CAUTION: Do not leave electrical current applied to the injector for longer than five seconds. Damage to injector coil or internal injector seals (Fig. 10) could result.

The only thing common to the injectors is the ASD relay, but it's common to all 8.  The ASD relay supplies power to the injectors at start-up, but when the engine is running, power is supplied by the charging system.  The PCM switches the ground to direct the firing of the injectors.  If the injectors all test OK, I'd suspect a bad injector driver in the PCM - not repairable, so that would mean a replacement PCM.  The misfire code could be caused by bad spark plug/wire as well (if it's a misfire code, and not Injector Control Circuit - the P code would help)

[mayfair]

To check injectors:

To test the injector only, disconnect the fuel injector wire harness connector from the injector. Place an ohmmeter across the injector terminals. Resistance reading should be approximately 12 ohms +/- 1.2 ohms at 20°C (68°F) .

CAUTION: Do not leave electrical current applied to the injector for longer than five seconds. Damage to injector coil or internal injector seals (Fig. 10) could result.

The only thing common to the injectors is the ASD relay, but it's common to all 8.  The ASD relay supplies power to the injectors at start-up, but when the engine is running, power is supplied by the charging system.  The PCM switches the ground to direct the firing of the injectors.  If the injectors all test OK, I'd suspect a bad injector driver in the PCM - not repairable, so that would mean a replacement PCM.  The misfire code could be caused by bad spark plug/wire as well (if it's a misfire code, and not Injector Control Circuit - the P code would help)

Yeah, I was just gonna say that!

[kenz]

Thanks Tom, I'll pass it along. I'm thinking the injectors are good, and the problem could be electrical in nature. Just didn't know how the injectors were controlled. He has completely swapped all ignition parts....plugs, wires, etc. Was gonna change plugs again thinking maybe he fouled them out. I will pass along the injector test procedure. Could also check the charging system, just to make sure that is up to task. I will also try to get the actual code numbers.

Donny, you were right on the money, just a day late and a dollar short. 

[kenz]

UPDATE..... Well he did a compression test (local mechanic mentioned this) and found 0 comp. in #5 cylinder. Removed the valve cover and discovered a broken valve spring. So he is now replacing the spring and will see how it runs. This could explain why it just started to run bad all of a sudden, but doesn't explain the injector issue, especially with #5 cylinder. Will stay tuned with results.

[mayfair]

Is he replacing just the one spring, or all of them?

[kenz]

Not sure, but I'm suspecting just the one at least for the time being to get the problem straightened out.

[Motorbrreath]

ohm the wire from the injector to the pcm driver, if its low resistance, you most likely have a bad driver in the pcm

[bran_gun08]

Try changing the up stream o2 sensor

[kenz]

In talking to him the other day it appears that the whole problem was a broken valve spring. Replaced it, cleared any codes, and so far everything is good as gold. The only thing I can think of is that there was a bad injector on top of the broken spring, plus maybe a couple other small problems. So once all the obvious stuff was repaired, only then did the broken spring show up. Thanks for all the ideas, made the job a little easier.