injector help

Hey guys I installed some new injectors in my truck and am having some issues. The first time I started it up it was good, but the second time I fired it up it started to have a miss. I did a buzz test and they all sounded good, so I did a cylinder contribution test and 6 and 8 failed. So I pulled the injectors back out and everything looked good checked connections. So I put them back in and the miss went away, so the next morning I go to pull the truck out and the miss comes back. So I run the cylinder contribution test and now 1 and 3 failed. Just wondering what the heck could be going on. Any help would be awesome.

Sounds like a UVCH issue. Did you replace them?

It may also be a fuel issue or possibly an oil side issue. You gotta get rid of all the air in the system.

Yes I did replace them.

strok-n said:

Yes I did replace them.

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Did you do a buzz test yet?

Yes I did and they all sounded good.

It takes a long time to get the air all worked out of the hpo system after a injector change. I would run it hard and wait till you got a few miles on it, then see if it smooths out.

Honestly unless this is something SEVERE sounding like bent valve or push rod sounding, as there are misses then there are MISSES, I would run it for 50 miles and see if it goes away after that drive. But then for me that is just going to the closest grocery store and back LOL. But if its really bugging you why not make a video of the engine running and get the opinions of those on here.

If you will feel better testing things out some a sure fire way to rule out the electrical side of things is to OHM out the harness from the IDM connector. Pull the wheel well cover and unhook the IDM. Then with all the injectors and all plugged in ohm out all the pin outs from the IDM connector. This will cover the entire system from IDM to injectors.

Its up to you.

When you pulled them and put them back in did they go back in the same hole? Or did 6 and 8 go into 1 and 3 holes?

You did not use Dorman gaskets did you?

Hey I did OHM out the harness and everything was fine. When I pulled them I changed holes but kept them on the same side. 6 and 8 are good. I swapped 1 and 3 last night and now only 1 is having problems so I am thinking that one might an injector issue.

They are probably still eating some air and causing the miss you think is something bad. just run it for a bit and see if it changes

Some thoughts reviewing everything you have posted up as far as info goes:


I would not be going off the contribution test results with injectors that are not "broken in" per se. ( purged of air i.e at least 50 miles of actual driving)

I do not believe you can get a good accurate and consistent contribution test result without the injectors oil side fully purged of air etc.. The contribution test measure the timing and rotation velocity of the cam gear ..........which the entire cylinder effects this, but even if we went only with the effect of just the injector itself..... An injector with air in it is going to fire differently thus effecting the cylinders output as measured by the CPS reading the cam gear rotational specs.

Could a injector have an issue sure it COULD, its mechinical and that stuff can break or maybe not been built just right. At the same time there is no way to be sure if you do not give it a chance to clear the air so you can remove that possibility off the table.

Its not the Solenoid or armature clearance as you say they past the buzz test. You have ohm'd the wiring so it checks out.

The reports you are getting on the contribution test do not IMO support a single injector issue, as if it was, there would be a consistent single injector that the problem was with and it would follow that and only that injector. Both 6 @ 8 failed and then you pulled and reinstalled swapping all the injectors around within each bank. It was not indicated if you actually mapped where each one went from each original hole on the swap. You then ended up with 1&3 failed. Then you swapped 1 and 3 with each other which were BOTH failing and now 1 is the only one failing? How did the other fix itself?

In the beginning it was 6&8 then 1&3 and now just 1. What is more likely to be happening:

1: Some bad injectors have fixed themselves or otherwise worked out their issues leaving only one that seems to be actually need some help.

2: Air is slowly moving thru the system and working its way out as well as being effected by the various pulling and swapping around of injectors and thus effecting the way the injectors are firing which is effecting the results of the contribution test.


It could be possible a combo of both but again no way to be sure without eliminating the possibility of air.

If this was a severe miss I would think you should be able to easily follow it by sound alone with the VC off.


Also want to point out that the new versions of the CPS all can cause some cylinders to fail the test when there is nothing mechanically wrong except with the damn cheap @ss CPS itself. So nothing wrong within the cylinders.

Another is when injectors are first installed and even then you can sometimes run a number of contribution tests and get varying reports. It sometimes takes a number of runs to get a consistent reading.

Hey guys well ended up putting a new injector in and it looked like that was gonna fix it but today after running it for a good 70 miles I am driving home and it started to sound like it was missing. I ran the contribution test and now 2 and 7 are failing. I am nervous to keep driving it cause the motor is brand new. I could sure use some more input.

OK so you have driven it far enough for all the injectors to be clear

You ohm out the complete wiring harness from the IDM connector and it was good.

Do you notice the miss while driving it sound or performance wise or only at idle?

You should really make a video of it and lets hear what it sounds like.

IPR sleeve nut is not loose is it?

How does your oil look after running it a bit foaming or lots of bubbles?

Who's injectors are you running btw and what are the specs?

Also the specs on this new engine turbo HPOP fuel system?

I noticed the miss while driving based off sound. The idle is very choppy. IPR sleeve nut is tight. Did not check the oil. I am running Farmers Double D's 400/400. The motor is bored .20 over, hypermax rods, complete seal rings, girdle, ported and polished heads. HPOP is terminators, fuel system is a custom made regulated return. I am starting to lean towards a tuning issue because the miss only occurs at idle and light throttle. If I apply more throttle the miss goes away and the truck runs good.

strok-n said:

I noticed the miss while driving based off sound. The idle is very choppy. IPR sleeve nut is tight. Did not check the oil. I am running Farmers Double D's 400/400. The motor is bored .20 over, hypermax rods, complete seal rings, girdle, ported and polished heads. HPOP is terminators, fuel system is a custom made regulated return. I am starting to lean towards a tuning issue because the miss only occurs at idle and light throttle. If I apply more throttle the miss goes away and the truck runs good.

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Who did your tuning?

400/400's have a really choppy idle... Which could be what you're mistaking for a miss. Of course this is all dependent on tuning too.

strok-n said:

I noticed the miss while driving based off sound. The idle is very choppy. IPR sleeve nut is tight. Did not check the oil. I am running Farmers Double D's 400/400. The motor is bored .20 over, hypermax rods, complete seal rings, girdle, ported and polished heads. HPOP is terminators, fuel system is a custom made regulated return. I am starting to lean towards a tuning issue because the miss only occurs at idle and light throttle. If I apply more throttle the miss goes away and the truck runs good.

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For one quit pulling them in and out.... your subjecting yourself to crap in the HPO system that likes to plug IPRS....

Next run it for a while with them all in and stop running cont tests for a while....

Third you have HUGE nozzles... your going to need to get your tunes adjusted..... Sounds to me like when the oil is thin your having a "miss"

I am running DP Tuning.

CCT is not a fail proof test to fail a hole.

Pull the valve covers and check all 4 with a strait edge on both banks.

If all are good (1 isn't sitting high) run it). Btw running hard isn't the best way to get the air out. You need to work the hpop system. So high DC under a good load will really get her moving through the system. Charles explained it really well in a thread a while back and for the life of me cannot find it.

If your going from splits to singles that with the combo of air in the system will make you think you have a miss. It's just louder. Unplug one injector with it running. You will understand what a miss sounds like.

Wackerjr said:

For one quit pulling them in and out.... your subjecting yourself to crap in the HPO system that likes to plug IPRS....

Next run it for a while with them all in and stop running cont tests for a while....

Third you have HUGE nozzles... your going to need to get your tunes adjusted..... Sounds to me like when the oil is thin your having a "miss"

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Jeremy is right. A 400% nozzle will take a lot of tuning work to get a stockish idle.
How new are the injectors ? If the problem pertains after a while I would suspect a bad injector. I believe a slight miss at idle and fine otherwise is poppet valves ?
Don't worry mike will tell you how too pull your injector apart and clear it out if it's sticking :lookaround: