speed density/fuel injector compatibility

[302 coupe]

I just bought a 1988 Thunderbird LX and it has the non-HO 5.0L. Its a speed density setup, and has the xxx-A1C computer, which should be correct for the car. From my understanding, the car came stock with the gray top 14lb/hr injectors. The PO seems to have installed the orange top 19lb/hr injectors, without installing any other HO parts. The car has a surge at idle, and smells rich. Is it because of the 19lb injectors?

 

[Daggar]

It's possible that the 19 lbers could be causing a rich condition, but I think you need to get a handle on the surging idle first. Larger injectors or not, it shouldn't be continually surging at idle unless there's something else wrong. Speed density is VERY sensitive to vac leaks, crummy EGR and IACs, and of course, TPS settings.

I think I'd start by capping vac lines off one by one in hopes of finding one that makes a significant difference in how it idles. It may not be a bad idea to disconnect the 02 sensors just at the outside chance that AFR is crossing back and forth over the margain that it's able to read and trying to compensate.

On those HOs that I've put 24s in place of 19s (the ones that didn't like it), it did run rich but surging was not one of the sypmtoms.

I can't say for certain that the same would be true on your application.

 

[302 coupe]

it has a new EGR and TPS. I'll check the IAC and see if its clogged or anything.

Will the ecu cut back the duty cycle on the injectors to keep the right afr, to compensate for the bigger injectors?

 

[Daggar]

it has a new EGR and TPS. I'll check the IAC and see if its clogged or anything.

Will the ecu cut back the duty cycle on the injectors to keep the right afr, to compensate for the bigger injectors?

Jumping from 14 lbers to 19lbers is out of the scope of the 25% rule for the computer to be able to compensate for. What I don't know is what the injector breakpoints and Min pulse width is for a 14 lb injector. Those may or may not be within the 25%. I've never worked with a 14 lber before so I just don't know how they're setup.

As an example of what I'm talking about:

With a stock mass air EEC, you can run 19s, 24s, and 30 lb injectors without too much difficulty so long as the meter is calibrated to coincide with the injector. Their Mins and break points aren't too different from one another even though the amount of fuel each can deliver is considerably different. Try running 36s or 42s even WITH a cal'd meter and you start running into problems.

With the 14s, I just don't know how far apart those two things are when compared to a 19. It will depend on how they were designed.

Edit: On a side note though. If the injectors along with the stock EEC make a contiually rich condition, then the EEC will give up and run the preset fuel tables. I still shouldn't cause a surging problem. To a stock narrow band 02 sensor, rich is rich. It cannot determine how rich. The stock 02s act allot more like a switch than they do a an actual sensor.

 

[craZy400]

similar question

I have NEW grey top injectors off of an '86 5.0 H.O. which are 140cc @ 3bar that I was hoping to replace my OLD orange top 194cc @ 3bar with.

Will this cause a lean condition?

Will the computer adjust for this?

I have the ENTIRE fuel injection system so if I swap all of it at once will the '92 computer compensate for it?

Any help would be appreciated.
Thanks
Ty