Replacing multec injectors
Thread Starter
Cruising
Joined: Jul 2020
Posts: 14
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Replacing multec injectors
Hi. One of my multec injectors is showing only 1 ohm resistance, so I'll be changing the injectors. I have decided I will use OEM style injectors from Rockauto. More precisely the SMP FJ47 or SKP SKFJ10024. Are there any known problems with these? I dont want to buy the FIC bosch 3s as they wont be a perfect fit and my car is stock.
So, which one should I buy, SMP or SKP?
So, which one should I buy, SMP or SKP?
Pro
Joined: May 2025
Posts: 584
Likes: 130
From: OK
I don't believe any of the random asian reman/new injectors have especially good reputations in general.
I also question if they are identical stock replacements or only stock size/shape with more modern/cheaper guts.
I forked over $450ish for set of the Delphi stock replacements from one of the recommended vendors recently with the hope that I could
avoid having to re-tune as folks so often do when going to the newer style ones but no such luck. My fuel trims immediately went wonky.
Not so much that the system can't correct for it, least on my car, but it's obvious it's having to work at it. If I had it to do over again
I'd have my stock ones rebuilt, and if I had one or two bad ones that wouldn't clean up I'd buy original used replacements till I found some
that would.
There was remarkably little difference in how mine ran with the 40 year old 156K injectors vs the shiny new ones.
Overall it was a disappointing, expensive annoying experience.
I also question if they are identical stock replacements or only stock size/shape with more modern/cheaper guts.
I forked over $450ish for set of the Delphi stock replacements from one of the recommended vendors recently with the hope that I could
avoid having to re-tune as folks so often do when going to the newer style ones but no such luck. My fuel trims immediately went wonky.
Not so much that the system can't correct for it, least on my car, but it's obvious it's having to work at it. If I had it to do over again
I'd have my stock ones rebuilt, and if I had one or two bad ones that wouldn't clean up I'd buy original used replacements till I found some
that would.
There was remarkably little difference in how mine ran with the 40 year old 156K injectors vs the shiny new ones.
Overall it was a disappointing, expensive annoying experience.
Melting Slicks
Joined: Aug 2011
Posts: 2,844
Likes: 176
Pro
Joined: May 2025
Posts: 584
Likes: 130
From: OK
Interesting, the delphi are rich, barely correctable at idle and a little better at speed. I've seen it suggested that
it's because they open and close so much faster that for a given duty cycle they are passing more fuel than the ECU
expects since the old injectors are slower to do so. One may well never notice this unless they are looking for it
from the ECU data, and I'm sure one motor to another varies.
it's because they open and close so much faster that for a given duty cycle they are passing more fuel than the ECU
expects since the old injectors are slower to do so. One may well never notice this unless they are looking for it
from the ECU data, and I'm sure one motor to another varies.
Melting Slicks
Joined: Jul 2005
Posts: 2,197
Likes: 302
But, once properly tuned for, they're fantastic injectors. Got some from Southbay a while back and they're awesome.
For someone with a stock car who wants hassle free replacement, then yeah I hear the Delphi's are the true drop-in replacements.
Melting Slicks
Joined: Jul 2005
Posts: 2,197
Likes: 302
Interesting, the delphi are rich, barely correctable at idle and a little better at speed. I've seen it suggested that
it's because they open and close so much faster that for a given duty cycle they are passing more fuel than the ECU
expects since the old injectors are slower to do so. One may well never notice this unless they are looking for it
from the ECU data, and I'm sure one motor to another varies.
it's because they open and close so much faster that for a given duty cycle they are passing more fuel than the ECU
expects since the old injectors are slower to do so. One may well never notice this unless they are looking for it
from the ECU data, and I'm sure one motor to another varies.
From what I understood it's because the old Multecs weren't very efficient at low PW's, so GM put in this "helper" table for low PW's. When you upgrade to modern injectors, they don't need that "helper" table, so if you don't zero it out, you'll get potentially significantly richer mixtures. The helper table can deliver up to ~0.5 millisconds... so if your base PW is say, 1.5 ms, you could be getting a ~30% richer mixture than needed.
DA2/DA3 has this table as well. But I don't see it in 6E... doesn't mean its not there, just that my particular ECM definition file doesn't have it.
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Melting Slicks
Joined: Aug 2011
Posts: 2,844
Likes: 176
Interesting, the delphi are rich, barely correctable at idle and a little better at speed. I've seen it suggested that
it's because they open and close so much faster that for a given duty cycle they are passing more fuel than the ECU
expects since the old injectors are slower to do so. One may well never notice this unless they are looking for it
from the ECU data, and I'm sure one motor to another varies.
it's because they open and close so much faster that for a given duty cycle they are passing more fuel than the ECU
expects since the old injectors are slower to do so. One may well never notice this unless they are looking for it
from the ECU data, and I'm sure one motor to another varies.
Melting Slicks
Joined: Aug 2011
Posts: 2,844
Likes: 176
That's been my experience as well with Bosch-III's.... BLMs sometimes shoot up into the 150 range, which then requires tuning.
But, once properly tuned for, they're fantastic injectors. Got some from Southbay a while back and they're awesome.
For someone with a stock car who wants hassle free replacement, then yeah I hear the Delphi's are the true drop-in replacements.
But, once properly tuned for, they're fantastic injectors. Got some from Southbay a while back and they're awesome.
For someone with a stock car who wants hassle free replacement, then yeah I hear the Delphi's are the true drop-in replacements.
Pro
Joined: May 2025
Posts: 584
Likes: 130
From: OK
I guess it's technically possible one is leaking but they were a matched set from Southbend so I doubt it. Not rich before, rich next day
after installing. Car runs just practically the same, been a few times I thought the crank time cold was a little long as I've seen reported
for other injectors but it's been inconsistent enough I wouldn't swear to it.
Melting Slicks
Joined: Jul 2005
Posts: 2,197
Likes: 302
Melting Slicks
Joined: May 2019
Posts: 3,137
Likes: 1,360
From: Mid-Atlantic
2025 C4 of the Year Finalist - Unmodified
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I just recently uninstalled a full set of Delphi injectors and replaced them with SouthBay's Bosch III injectors.
In hindsight, I really wish I'd just replaced the one bad Delphi injector versus all 8 injectors because the Delphi ones are just better injectors, in my opinion.
These Bosch ones tick like crazy and they're very loud. Drives me bonkers. It's almost embarrassing at a red light.
In hindsight, I really wish I'd just replaced the one bad Delphi injector versus all 8 injectors because the Delphi ones are just better injectors, in my opinion.
These Bosch ones tick like crazy and they're very loud. Drives me bonkers. It's almost embarrassing at a red light.
Melting Slicks
Joined: Jul 2005
Posts: 2,197
Likes: 302
I just recently uninstalled a full set of Delphi injectors and replaced them with SouthBay's Bosch III injectors.
In hindsight, I really wish I'd just replaced the one bad Delphi injector versus all 8 injectors because the Delphi ones are just better injectors, in my opinion.
These Bosch ones tick like crazy and they're very loud. Drives me bonkers. It's almost embarrassing at a red light.
In hindsight, I really wish I'd just replaced the one bad Delphi injector versus all 8 injectors because the Delphi ones are just better injectors, in my opinion.
These Bosch ones tick like crazy and they're very loud. Drives me bonkers. It's almost embarrassing at a red light.
Melting Slicks
Joined: May 2019
Posts: 3,137
Likes: 1,360
From: Mid-Atlantic
2025 C4 of the Year Finalist - Unmodified
2023 C4 of the Year Finalist - Unmodified
2022 C4 of the Year Finalist - Unmodified
2021 C4 of the Year - Unmodified Finalist
Melting Slicks
Joined: Jul 2005
Posts: 2,197
Likes: 302
Hah... that's me with noises on the inside of the car. Soon as I hear some squeak or something, I'm immediately going after it...