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Discussion Starter #1
Anyone have any tips for doing injectors on a 4.9? I'm putting in some 19pph Accel injectors in the next couple of weeks and wanted to see if anyone knew of any common problems/tricks. Thanks in advance.
D.
 

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1995 Sedan De Ville (4.9 L)
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I want to know the answer, too.

Once I have removed injectors and it seems that it might be a better
idea to connect the front fuel rail and the rear fuel rail BEFORE they
are attached on the engine block. Once both are attached to the
engine, they don't seem to align well and it is hard to put together.
But I am not sure if all injectors go right in the engine when both rails
are connected before installation...
 

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Discussion Starter #3
I did it, and it wasn't too bad. Have to disconnect the P.S. pump, egr valve, bunch of elec. connectors, coolant hose to thermostat housing, 2 fuel lines, and a bunch of other little stuff. Then there's about 5 bolts holding the rails in, and you pull em both off as an assembly (the two rails and the regulator). Then the injectors get switched and you put it back in. Took me just under 2 hours to do. Not anywhere near as bad as I'd feared. Performance went up nicely according to the seat-of-my-pants. :)
D.
 

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2001 DTS, 2005 Mustang GT, 2010 MINI S
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Hmmm....bigger injectors should not improve the feel at all. They may have better flow vs 100k injectors....hence a different feel.

See this with the Corvette guys all the time. Their 'solution' is to add a adjustable fuel pressure regulator....and try to boost the fuel pressure.

The problem is how the injectors work. The PCM quad driver drives the injectors. The 'on' time of the injectors is based on O2 bank sensor feedback to the PCM. There is a fuel map in the PCM. 128 is the center of the fuel map. If you increase the fuel flow the PCM reduces the pulse of the injector 'on' time and tries to get to 128. Also called the pulse width time.

You can see this data via the cluster diagnostics or a scan tool. If a engine is running lean the PCM will try to compensate and add fuel. You will see the long and short term fuel map go high such as maybe 145. If the car is running rich the PCM will pull fuel out.....you can see the fuel map run maybe at 90.

Higher flow injectors are a waste of money.

Logan
 

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Discussion Starter #5
Personally I think the improvement is from the spray pattern.. Stock injectors tend to shoot out a solid stream of gas, while aftermarket gives a nice cone-shape. I've seen the two side by side, it's quite a difference. Also, they have MUCH closer tolerances than the stock stuff. That means they're actually putting out the amount of fuel the cpu tells them to. The 1lb/hr increase is just enough that the computer can still control it without getting all wacked, and will provide more fuel on the top end at WOT where the cpu doesn't tune so much.
D.
 

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1995 Sedan De Ville (4.9 L)
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I see. Next time, I will connect the front and rear fuel rails
together before installing them on the engine.

And, OK, what Logandiagnostic says makes sense to me.
But I have heard that when you "wide open throttle", the
computer ignores feedback from the oxygen sensor and goes
in open loop mode while the throttle is wide open.

Well, to be honest, I don't remember very well, so I may be
wrong... What do you think?
 

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At WOT...the system already goes very rich on its own. This is to protect the engine. Much better to go too rich vs too lean. It protects the pistons etc from lean condition burn up. Hence the dark cloud you see behind you at WOT...its fuel.

Logan
 

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Logandiagnostic said:
At WOT...the system already goes very rich on its own. This is to protect the engine. Much better to go too rich vs too lean. It protects the pistons etc from lean condition burn up. Hence the dark cloud you see behind you at WOT...its fuel.

Logan
I see... So, does it mean using bigger injectors might make
difference at wide open throttle, because the oxygen sensor
does not compensate the amont of fuel??

Also, it may be right to conclude that bigger injectors don't
really change anything in closed loop, because the oxygen sensor
does adjust the amount of fuel??
 

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At WOT..the factory injectors are doing fine since excesive fuel is being burned off..hence the dark smoke you see at WOT.

The spray pattern mentioned in the earlier post...stream vs spray. Indicates that the original injectors were dirty or damaged.

The best test is to speed test the car. Many times the owners report a better 'feel' in the car. If you go run a 1/4 mile test the times are often slower with the new higher flow injectors.

Logan
 

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Yeah, you are right.

The best way to test the car is not discussing over the net, but
experimenting it on the road with instruments (even a simple stop
watch as you said!).
 
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