wabco40

I'm about to change the injectors on a 88. I have a set of 24lb injector which I plan to use. I'm also blocking off the ninth injector.
Can someone let me know if I will need to get the ECM chip retuned. The engine is completely stock other then headers and a 2 1/2" exhaust.

Brad

tunedport85inject

Stock are 22, you have to set 24 on injector flow rate scalar in the bin, or the ECM constantly reduces injectors pulse width...

wabco40

Say wot?

vader86

No, you don't really have to have the chip retuned, its not so far out of the spec 22lb/hr that the ECM cannot adjust the pulse width to compensate for.

I would have an adjustable regular put on with the new injectors though, just in case you need to tweak it.

tunedport85inject

Since ECM compensates the unexpected highier flow rate, the BLM's go in the low 110's and the car smells of fuel ...this happen to me....

The ECM doesn't know you'r running bigger injectors (24lb vs 22),being fuel pressure the same (43psi),you pump more fuel than expected into combustions chambers,in closed loop, your O2 sensor read a richer air-fuel mixture ,suddenly ECM cuts the injectors pulse width to compensate,this translate into a low blm's in the 110-112 range.A richer air fuel ratio doesn't produce best performance,in this condition your wot enrichment stays in the 10,5 :1 and you lost hp vs a better 12,8-13 afr

1985 one year C4 used 24 lbh injectors but they were presurizzed at 35-38psi it equals 22lbh at 43 psi.A best pattern atomization comes with highier fuel pressure ,it's best a 22lb injector fired under 43 psi than a 24lb fired under 35psi cuz best atomization = best combustion

MrWillys

An 88 ABTR BCC was programmed at 23 lbs. What is your BCC (broadcast code)? It may work, but as has already been suggested the ecm will be removing fuel and your BLM counts will run low. The correlation between fuel pressure, injector size, and programmed flowrate is very important. It would be ignorant to dismiss how critical this can be, because a power increase would be a misconception.

wabco40

Thanks for the replies.

I might be better if I just order a set of 22lb from FIC.

Benny42

I had a set of 24# in a '89 Formula 350. It was otherwise all stock and it passed Texas smog
and never set a code. It was probably always compensating but it got decent mileage and
ran very well.

Cliff Harris

One problem with the higher flow rate injectors is that the ECM does not adjust BLMs in open loop mode.

You will run rich when the engine is cold until it goes into closed loop mode. Then the ECM will back off on the injector pulse width to achieve 14.7:1 AFR. The net gain is zero.

tunedport85inject

But... If you'r planning future modds, like heads/ cams you can put 24 in the meawhile even if you may loose some fuel milleage or run a little rich

vader86

I'm aware of this stuff, ECM won't be able to adjust in open loop.

However if he intends to further modify the engine the loss of mileage isn't a big problem here, and it wont be so pig rich that it can't be driven.

samsonb

There were 24# Accel injectors in mine, and it ran rich and fouled out the plugs. Put in 22# FIC Bosch III, and it ran super lean i.e. BLM 160. Ended up with 24# FIC Bosch III and the BLM's were right in spec.