Injector question [Archive] - GrandAmGT.com Forum

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Azazel
08-12-2012, 10:24 PM
I also posted this in the Performance section because of the aftermarket injectors to see if any of the Performance guys could help me out. So i was having many misfire codes on my 99GA and i basically pinpointed it to the injectors, the car has over 150k miles so its not a total shock. I bought new 42lb injectors from MMS and finally had the time to do the job. I also replaced the LIM because it was !TOAST! I haven't been driving the car for a long time because it has been so bad. Anyways i replaced the LIM and the injectors and now the car idles like GARBAGE and i can not for the life of me figure out why.
Im wondering if its the injectors being so much larger than stock or have a bad spray pattern or i did something wrong putting it all back together.... I triple checked the wiring including the spark plug wires, all is good. I am totally lost.
Do i go buy new stock injectors and find out that that was not the problem? Or is there some tuning i HAVE to do to make it work? Anyone? Thanks

chris_gt_74
08-12-2012, 10:31 PM
Your pcm needs tuned. #42 injectors are quite a bit more flow than stock.

Azazel
08-12-2012, 10:36 PM
Your pcm needs tuned. #42 injectors are quite a bit more flow than stock.

Ok any direction on the tuning? I do have a tuner for the car.

Starglow
08-13-2012, 11:11 AM
Ok any direction on the tuning? I do have a tuner for the car.

It would be best to talk with Mike at MMS for specific tuning advice. If you spliced in new injector connectors are you sure the electrical connections are good? Also check for vacuum leaks around the UIM, TB gaskets, and vacuum hoses.

Other than that we'd need a more detailed problem description beyond "Like Garbage" to understand what's going on. How does the car run under normal driving conditions... etc.

AaronGTR
08-13-2012, 03:12 PM
Yeah, you need to tune the PCM for the injectors first. You can't just swap them in and expect it to run right. :rolleyes:

G.I.Ceo
08-13-2012, 05:52 PM
What tuner are you using? I believe I have the table for the 42lb injectors but it using DHP tuning. But like everyone else says you haveto have it tuned to make those work correctly or go back to stock ones.

Azazel
08-13-2012, 09:11 PM
What tuner are you using? I believe I have the table for the 42lb injectors but it using DHP tuning. But like everyone else says you haveto have it tuned to make those work correctly or go back to stock ones.

I have the DHP tuner any help would be awesome!

Azazel
08-13-2012, 09:16 PM
It would be best to talk with Mike at MMS for specific tuning advice. If you spliced in new injector connectors are you sure the electrical connections are good? Also check for vacuum leaks around the UIM, TB gaskets, and vacuum hoses.

Other than that we'd need a more detailed problem description beyond "Like Garbage" to understand what's going on. How does the car run under normal driving conditions... etc.

I didn't have to splice anything as mine is a 99. The car doesn't run well enough to even move at the moment. Idles really rough like its miss firing on all cylinders. I haven't been able to hook up the tuner to it to read whatever codes its throwing because my laptop is currently a paper weight. I'm borrowing my brothers tonight and am going to load the software on and check it out.

G.I.Ceo
08-13-2012, 09:33 PM
I have the DHP tuner any help would be awesome!
Let me look and see if I have the table.

AaronGTR
08-13-2012, 10:26 PM
Set the IFR table (injector flow rate) to around 196 g/sec across the board. That's a good starting point for 42 lb/hr injectors. You'll find it in the fueling folder.

Of course after you get the software loaded and set up on the laptop, you are going to have to do a PCM read first to get your stock program. Do a read, open the bin file and modify the IFR table, save, do a partial write to your PCM (should take around 60 seconds).

AleroB888
08-13-2012, 10:59 PM
Set the IFR table (injector flow rate) to around 196 g/sec across the board. That's a good starting point for 42 lb/hr injectors. You'll find it in the fueling folder.

Of course after you get the software loaded and set up on the laptop, you are going to have to do a PCM read first to get your stock program. Do a read, open the bin file and modify the IFR table, save, do a partial write to your PCM (should take around 60 seconds).

Don't forget to allow for the difference in fuel pressure between models--

Fuel pressure reading @ key on, engine off:
1999 pressure specification is 41-47 psi,
00-05 pressure specification is 52-59

My '99 ran at about 35-38 psi fuel pressure stock, 43-48 with an '03 regulator.

Azazel
08-13-2012, 11:13 PM
Set the IFR table (injector flow rate) to around 196 g/sec across the board. That's a good starting point for 42 lb/hr injectors. You'll find it in the fueling folder.

Of course after you get the software loaded and set up on the laptop, you are going to have to do a PCM read first to get your stock program. Do a read, open the bin file and modify the IFR table, save, do a partial write to your PCM (should take around 60 seconds).

Thanks for the info, I have played with the software a lot in the past but for the last few years my life has taken me away from the fun of the car. The part of my brain that has all the tuning info seems to have shut off.

In what increments should i change the values for fine tuning?

Don't forget to allow for the difference in fuel pressure between models--



What would the compensation for that be?

AleroB888
08-14-2012, 08:01 AM
What would the compensation for that be?

http://www.rceng.com/technical.aspx?UserID=900012&SessionID=qossjMkuu9gUIyY3HAif#Find_Fuel_Flow_Afte r_Pressure_Change

Azazel
08-15-2012, 02:05 AM
Is there a place to find the fuel pressure on the DHP? Or do i need to go get a new pressure tester?

AleroB888
08-15-2012, 07:29 AM
Is there a place to find the fuel pressure on the DHP? Or do i need to go get a new pressure tester?

No, if it's a 1999, for the time being consider it to be 37 psi. Verify it if you get it running.

AaronGTR
08-15-2012, 09:22 PM
Yeah, there is no factory fuel pressure sensor (just like there is no factory oil pressure sensor). You have to hook a mechanical gauge to the end of the fuel rail, or get an aftermarket fuel pressure gauge with a sending unit and hook it up.