Question about my 550 injectors!

[JDR7919]

Ok so I have been having a problem with overrunning my injectors. Boost was like 18-20 and I was getting 105 to 150 duty cycle. So I turn the boost down to 10psi and Im still getting up to 109%.

How could I be getting such high duty cycle on such a low amount of boost?



I have looked for boost leaks ect ect.

 

[oddrob]

What are your airflow numbers? That would correlate a problem.

 

[JDR7919]

I have never logged air flow before what should I look for that would be a problem?

 

[94Jettameowpsst]

If your idcs are that high with that low of boost, id look for airflow hz under 1000. It sounds as if your injector o rings arent sealing tho.....a boost leak of that proportion would make your car run like crap dumping that much fuel...you probably wouldnt even be able to floor it without it bogging out

 

[JDR7919]

Well the car seems to run ok I dont think I have ever had it tuned great. It pulls smooth I start getting knock at 4300rpm the same time the dutycycle goes through the roof.
So how do I check the rings on the injectors to make sure they are sealing? If they are not sealing and I replace them should that help the high dc?

 

[94Jettameowpsst]

Do a leak down test to determine if they're sealed. But what are your afc settings...cause you could just be VERY rich.....but at the same time your whole situation doesnt make sense to me. I think a boost leak or leaky injector seals are the only things besides actual overrunning that causes high idcs. Id look at those first 2 things before you look elsewhere.

 

[JDR7919]

I only have MAFT 2.xx I will do I leak test again. So i would hear air coming out of the fuel rail right?

 

[94Jettameowpsst]

Yes.

 

[GVR4592]

What is your base fuel pressure with the vacuum line unplugged?

 

[92GSXBaltimore]

What is your base fuel pressure with the vacuum line unplugged?

yeah, Im thinking his base pressure is low. Check your base fuel pressure, and replace your fuel filter if it is old, also check your injector o-rings.

 

[JDR7919]

Base fuel pressure is about 43 with the vac off and 37 to 38 with it on.

I found a small leak and fixed that. I also pulled off the injectors and found two small tears in 2 of the o-rings. So I replaced all the o-rings and went for a ride. Here is a third gear log on about 14 psi with 5 gallons of 100 oct. Fuel filter is new.

Rpms knock Airflow inj/dc
2187 0 333 10
2562 0 529 20
2625 0 567 21
3250 0 774 32
3750 0 907 39
4062 1 1058 46
4312 0 1159 52
4531 0 1348 61
5093 0 1606 82
5375 1 1606 94
5718 0 1606 100
5875 6 1606 101
6218 12 1606 104
6562 17 1606 107
6906 17 1606 107
7093 17 1606 50

I have my wot zeroed out. Should I try leaning it out?

 

[GVR4592]

Is your fuel pump rewired? Could be a pump issue, low volume from the pump can cause high d/c and a lean condition.

 

[GVR4592]

Is your fuel pump rewired? Could be a pump issue, low volume from the pump can cause high d/c and a lean condition. I know absolutely nothing about the maft, so it could be related to that, maybe somebody with experience in that department could help out.