Is it time for new injectors??? OHM test
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Is it time for new injectors??? OHM test
Hi, I recently bought a 2004 4.6l f150 sxt ext cab with 150,000 miles and it had a misfire.
I bought it from the county with a pretty good maintenance history but the #1 coil and injector were unplugged when I bought it. I've since cleaned it up and just finished putting in new plugs and coil packs this morning. After I fired it up for the first time the CEL went out for a few minutes and then popped back on.
I scanned it for codes before the plugs and coils and got P0301 and P0306 (misfire in #1 and #6)
After the CEL came back on after I replaced the plugs and coils I got P0301 (misfire in #1) and a NOX below threshold I'm assuming is misfire related.
I just finished letting the truck cool down a bit and did an OHM test on the injectors (I couldn't reach #4 and #8)
4)???
???
3)9.8 7)26.6
2)3.8 6)16.7
1)3.6 5)12.8
Maintenance records show it got a coil 11/27/17
and a fuel injector and coil 7/28/14
and oil changes every 3000 miles
It doesn't show which cylinder got the coils and injector.
My ohm reading are all over the map. I made sure I had firm pressure on the contacts and waited until the readings were stable before I wrote them down. From my research 11-18 ohms is normal range??? Correct me if I'm wrong.
So if my research and readings are correct it looks like a new set of injectors are in order.
Is there anything else I should check (PCM?)
I bought it from the county with a pretty good maintenance history but the #1 coil and injector were unplugged when I bought it. I've since cleaned it up and just finished putting in new plugs and coil packs this morning. After I fired it up for the first time the CEL went out for a few minutes and then popped back on.
I scanned it for codes before the plugs and coils and got P0301 and P0306 (misfire in #1 and #6)
After the CEL came back on after I replaced the plugs and coils I got P0301 (misfire in #1) and a NOX below threshold I'm assuming is misfire related.
I just finished letting the truck cool down a bit and did an OHM test on the injectors (I couldn't reach #4 and #8)
4)???
???3)9.8 7)26.6
2)3.8 6)16.7
1)3.6 5)12.8
Maintenance records show it got a coil 11/27/17
and a fuel injector and coil 7/28/14
and oil changes every 3000 miles
It doesn't show which cylinder got the coils and injector.
My ohm reading are all over the map. I made sure I had firm pressure on the contacts and waited until the readings were stable before I wrote them down. From my research 11-18 ohms is normal range??? Correct me if I'm wrong.
So if my research and readings are correct it looks like a new set of injectors are in order.
Is there anything else I should check (PCM?)
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From: Washington
Injectors don't usually fail that way. Your resistance readings are odd. Might be replacing the injectors for the wrong reason.
Since your problem is on #1, replacing just #1 injector seems most sensible, to start. Or just one bank, since you'll have them all out. Could be that cylinder #1 has some other problem also. Comparing cylinder pressure to known good cylinders might tell you something. I'd check cylinder pressures first, since it's easy to do.
Since you have 7 good cylinders, by the codes anyway, beware of screwing up something new while you're in there. Good luck.
Since your problem is on #1, replacing just #1 injector seems most sensible, to start. Or just one bank, since you'll have them all out. Could be that cylinder #1 has some other problem also. Comparing cylinder pressure to known good cylinders might tell you something. I'd check cylinder pressures first, since it's easy to do.
Since you have 7 good cylinders, by the codes anyway, beware of screwing up something new while you're in there. Good luck.
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From: Washington
Another thing - if injector #1 has been disconnected that means it hasn't been opening. Fuel has been sitting in it, cooking. Plus the cylinder hasn't seen any fire, so the compression rings could be gummed up. You might take the truck out and give it a few on-ramp blasts to get fuel through that injector and to loosen things up. Hope that cylinder heals itself.
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Yeah....this is the first time I've done an injector OHM test. Like I said I have a new set ordered and I'll be replacing them all just to get fresh one's in there. The truck has 152,000 miles on it. Also from my test the problem cylinder #1 was the injector that tested the lowest of the 6 I was able to get to. I just can't figure out why the readings are all over the map so to speak. From my readings they should usually be within 2-3 ohms of each other? But I'm going to test the new injectors when they get here before I install them just out of curiosity. I'll keep the thread updated and let y'all know what happens. Any other thoughts or ideas would be much appreciated.
Thanks
PS I added half a can of seafoam to the fuel tank when I was doing the plugs/coils and ran the other half through the brake booster into the intake. Also sprayed about a can of carb/injector cleaner down the spark plug holes the night before I replaced the plugs
Thanks
PS I added half a can of seafoam to the fuel tank when I was doing the plugs/coils and ran the other half through the brake booster into the intake. Also sprayed about a can of carb/injector cleaner down the spark plug holes the night before I replaced the plugs
Last edited by green2man0; Jan 27, 2019 at 07:53 PM.
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From: Idaho
I agree with Bones. You have 7 good cylinders. I would try to go after one problem at a time so I didn't introduce a new issue without knowing it. When it comes to part new stands for "never ever worked". Not saying not to replace the injectors but go after one thing at a time. Good luck.
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Another thing - if injector #1 has been disconnected that means it hasn't been opening. Fuel has been sitting in it, cooking. Plus the cylinder hasn't seen any fire, so the compression rings could be gummed up. You might take the truck out and give it a few on-ramp blasts to get fuel through that injector and to loosen things up. Hope that cylinder heals itself.
Seafoam, carb cleaner, random parts replacement...all just guesses anyway.
Check your meter also. It might have a dying battery. The meter battery supplies the juice for the resistance measurements.
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I pulled the injectors off the rail today. I switched out the battery in my multimeter and got totally different readings....does temperature play a huge role in OHM tests? My problem cylinder (#1 injector/cylinder) injector is the only one of the 8 that has some kind of whiteish sludge on the tip covering the output holes...all the others are clean and shiny metal and you can see the spray holes. I'm gonna let all the injectors come to room temperature and test them again but I'm getting 18.7-23.4 ohms throughout the 8.
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Well I got my injectors, but I think they shipped the wrong ones...I'm waiting to be emailed back. There's no marking on the body and physically they look identical to the OEM ones. The only exception is they have green bands around the base instead of the stock white ones and the box had a note on it with 1f1e-d4a which I looked up the pn and they're 19# the same as the f150 but show fitment for 3.0 ranger and taurus. Can anyone help cross reference the pn. The stock pn should be 4L3E-B4C.I want to make sure they're right or will work before I go installing them.