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New injectors, now VP shows weakness...


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Hey guys, ill try to keep this short. I got some 7x.009 dfi injectors last month. After installing these, my truck has a rough idle when engine temps are hot. I had these sent to chris at dfi and the injectors are all pop tested and flow at 300 bar. My install was good all new orings and copper washers no scoring on crossover tubes When i had my stock injectors in i had no rough idle at all, no hard starts, and no fuel leaks. Truck has had raptor 150 since ive owned it 19 psi idle 15-16 wide open. No check engine lights since ive owned the truck. But when i bought truck last september it has 8psi idle with factory pumpWhich is now leading me to believe that because im forcing more fuel at idle at the VP its showing a sign that it might be tuckering out???also its a reman vp on the truck now and i have no clue on the miles. I guess my question is are these injectors showing me my VP is shot or i missing some high pressure leak in fuel lines. Sucking air so to speak. At idle with these installed it feels as if i have a line cracked open at head, but if i reinstall stock injectors idle miss goes away...let me know what ya think. And i appreciate any input gary

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When installing the injector did you tighten the crossover tubes first or the injectors hold down caps?Correct answer is crossover should be first other wise the crossover tubes can't be seated correctly because the injector hold down caps should be loose so the injector can wiggle into position. So now you might have a high pressure leak inside the return rail and never see it but the engine will run as you describe.

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First of all, you are not forcing more fuel at an idle. Your truck only uses the correct amount for a given RPM. Any more and it will be running at a higher RPM. You say there is a miss when idling and it goes away with stock injectors. Is it a constant miss? Do you know what cylinder it is? You can check the temps of the individual exhaust runners to see which one(s) are running cooler than the rest. Have you tried swapping injectors to see it the miss follows the injector(s)? Sounds to me like one or more needs some attention.

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First time around i tightened hold downs, then sent them bak to have them all checked and flow matched. 2nd time i installed i tightened tubes first then hold downs. I just got them back in tuesday so im going to crack lines and see if 1 is worse than rest.

When installing the injector did you tighten the crossover tubes first or the injectors hold down caps?

Correct answer is crossover should be first other wise the crossover tubes can't be seated correctly because the injector hold down caps should be loose so the injector can wiggle into position. So now you might have a high pressure leak inside the return rail and never see it but the engine will run as you describe.

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The miss is only when truck has been running for 15-20min engine is warm 180-190. It is not a lope, the tach will bounce slightly and truck will even shake as it misses. Can also hear it in exhaust if standing behind truck. When stock injectors are back in all those symptoms are gone.

First of all, you are not forcing more fuel at an idle. Your truck only uses the correct amount for a given RPM. Any more and it will be running at a higher RPM. You say there is a miss when idling and it goes away with stock injectors. Is it a constant miss? Do you know what cylinder it is? You can check the temps of the individual exhaust runners to see which one(s) are running cooler than the rest. Have you tried swapping injectors to see it the miss follows the injector(s)? Sounds to me like one or more needs some attention.

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:duh:Take them to a local diesel shop and watch them test the injectors. All my injectors are tested in front of me I'm able to watch the pop pressure, spray pattern and if the injector is pissy or not. I typically don't pay anything for pop testing it only when the injectors have to be tuned I pay $15 a injector. Sound like you install them correctly the second time. But it still sound like a classic injecotr problem more so than injection pump. If it was the injection pump it typically doesn't matter what the temp of the engine is it will do it all the the time. But as a injector get hot they tend to fail and misfire but cold they work fine.

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I would assume local dodge dealer would be able to test these?.?.?. what about electronics on top of VP?

:duh: Take them to a local diesel shop and watch them test the injectors. All my injectors are tested in front of me I'm able to watch the pop pressure, spray pattern and if the injector is pissy or not. I typically don't pay anything for pop testing it only when the injectors have to be tuned I pay $15 a injector. Sound like you install them correctly the second time. But it still sound like a classic injecotr problem more so than injection pump. If it was the injection pump it typically doesn't matter what the temp of the engine is it will do it all the the time. But as a injector get hot they tend to fail and misfire but cold they work fine.

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I would assume local dodge dealer would be able to test these?.?.?. what about electronics on top of VP?

No. Typically I would say most dealers would send them out to be tested. Like around me there isn't a single dealer capable of pop testing. But now a diesel injection shop would. Electronics on top of the VP44 typically once they start to fail the continue to fail all the time. If the fuel pressure is greater than 14 PSI then the electronics will be at the temperature of the fuel regardless of the engine temperature. Typically the fuel temperature is <120*F so that's not going to be it either. But now the injectors while cold will have nice tight tolerances and fire nicely while the engine is cold but now get coolant temperature up and the tolerances of the pintle needle and the nozzle start to get a bit sloppy and end up with pissy injectors which is your misfire issue most likely. This why I suggest you take them and test them at least that is a low cost or free test. As for condemning the VP44 I have a rule of requiring 2 smoking guns. In other words I would require like low fuel pressure (<10 PSI) and P0216 error code. Then I'd say yes the VP44 is done time to replace. But we don't have that yet.
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  • 2 weeks later...

But why would it run right with the stock injectors and not with the bigger injectors? The the damaged connector tube would most likely repeat the problem regardless of the injectors wouldn't it? :think:

perhaps the vp is only strong enough to pop the stock injectors on time given the age and such of them (they aged together) put the new ones on and the vp cant pop them on time correctly due to them being newer and flow more. or even pop the new ones at all at idle? like giving an old man a Ferrari and taking away his model T, he aint gonna drive that ferarri right. just a thought
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perhaps the vp is only strong enough to pop the stock injectors on time given the age and such of them (they aged together) put the new ones on and the vp cant pop them on time correctly due to them being newer and flow more. or even pop the new ones at all at idle? like giving an old man a Ferrari and taking away his model T, he aint gonna drive that ferarri right. just a thought

If this is true, why would it miss only when coolant temps are up to 180-190? When i first get in and fire it up it idles just as it should....
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I would for the fun of it have the stock injectors pop tested and see if there is a serious difference in the stock vs. new injectors and see what the pop pressure are for both batches. But if both are popping at the same pressure them injectors wouldn't be the cause.

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I would for the fun of it have the stock injectors pop tested and see if there is a serious difference in the stock vs. new injectors and see what the pop pressure are for both batches. But if both are popping at the same pressure them injectors wouldn't be the cause.

I would love to but. Local shop is $90 a set. Maybe i could just have the stockers done just to see.
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I would love to but. Local shop is $90 a set. Maybe i could just have the stockers done just to see.

Wow! :stuned: Even my un-local injection shop 120 miles away in Lewiston, ID will pop test for free but charge $15 a injector for re-tune which is $90 for all 6 again. But the initial pop test is free though. I would do a bit of calling around and see what you turn up. What hang me up is everytime you put the aftermarket injectors back in the problem is back but the stock injectors are fine. Now as you give more throttle the injection pump creates more pressure increasing the amount of fuel sprayed. So if there was injection pump issue I would think you would see high end power loss not idle issues. As for crossover tube if they are damaged then it wouldn't matter what set of injectors it would do it with both. So that still leads me back to the injectors. Just thinking out loud.
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