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dcb 01-23-2009 04:30 AM

late 80's early 90's GM TBI advisory
Coyote x has conclusively identified an incompatibility with at least some late '80s and early 90's GM vehicles with "Peak and Hold" injectors. It will result in lower than actual fuel consumption readings. We are working on a fix in this thread:

You may be able to identify your injector type by disconnecting it and measuring its resistance, where low (2-5) ohms would indicate a Peak and hold, and high (10-15) ohms would be a saturation type. Coyote X describes his approach below in post #3.


dcb 01-23-2009 05:49 AM

Here's some more candidates for peak and hold (saturated should work fine):

Peak / Hold VS Saturated Injectors

Vehicle Injector Types Factory Flow Rating Notes
1990-'93 Geo Storm GSi Peak and Hold 222cc
1990-'93 Geo Storm 2+2 & Stylus S Saturated 222cc
1990-'93 Isuzu Impulse & Stylus XS Peak and Hold 222cc
1991-'92 Isuzu Impulse RS AWD Peak and Hold 322cc
1988-'91 Civic Si/CRX Si Peak and Hold 240cc
1992-'95 Civic Saturated 240cc
1996-'00 Civic dx cx and lx Saturated 190cc
1996-'00 Civic ex/si Saturated 240cc
1990-'91 Integra RS/LS/GS Peak and Hold 240cc
1992-'00 Integra LS/GS Saturated 240cc
1992-'96 Prelude Non-VTEC Peak and Hold 240cc
1992-'96 Prelude VTEC Peak and Hold 345cc
1997-up Prelude VTEC H22 Saturated 280cc
1991-up Sentra SE-R/200SX SE-R Saturated 265cc
1991-up MR2 Turbo Peak and Hold 440cc
1987-'92 Supra Turbo Peak and Hold 440cc
1993-up Supra non-Turbo Saturated 315cc
1993-up Supra Twin-Turbo Peak and Hold 550cc
2000-up Celica GT-S Saturated 310cc
1990-up Miata 1.6-liter Saturated 215cc
1993-up Miata 1.8-liter Saturated 240cc
1984-85 RX-7 195500-0900 Peak and Hold 680cc Orange Top
1986-87 RX-7 195500-1350 Peak and Hold 460cc Red Top
1986-87 RX-7 195500-1370 Peak and Hold 550cc Tan Top
1988 RX-7 195500-1350 Saturated 460cc Purple Top
1988 RX-7 195500-1370 Saturated 550cc Purple Top
1989-91 RX-7 195500-2010 Saturated 460cc Red Top
1989-91 RX-7 195500-2020 Saturated 550cc Purple Top
1993-up RX-7 Twin-Turbo Saturated Primary 550cc Secondary 850cc
1990-'96 300ZX Twin-Turbo Saturated 370cc
1991-up 3000GT/Dodge Stealth non-turbo Saturated 210cc
1991-up 3000GT VR-4/ Dodge Stealth R/T TT Peak and Hold 360cc
1989-up Eclipse/Laser/Talon Turbo/non-turbo Peak and Hold 450cc Blue Top(95+ Black top)
390cc Tan top
240cc Orange/pink Top
210cc Light Tan Top
Mitsubishi EVO Peak and Hold 510cc Yellow Top (1-3) 560cc Red top (4+)
1986-89 Ford turboCoupe Peak and Hold 35lb/hr Brown Top 30lb/hr Green Top

Coyote X 01-23-2009 11:11 AM

woohoo I'm a troublemaker :)

BTW I wasn't just in neutral. I was in drive holding the brakes to keep it from moving and using the torque converter as the load. So for an automatic trans that is the easy way to find out. For a manual trans I would suggest driving in a high gear and increasing the load going from holding speed/light throttle to wide open slowly (~3-5 seconds) and the gph value will stop increasing at some point. It doesn't show up on my tests till around half throttle so there needs to be enough load on the engine to keep it from accelerating faster than the display can keep up with.

dcb 01-23-2009 12:33 PM

Still trying to define the scope of the problem.

According to this : RC Injector Tech Note

written on 10/1998
"At this time, - 90% - of all automobiles, including the Japanese, are using Saturated - 12 to 16 Ohm Injectors. Toyota uses Sat. injectors in all but the Turbo Models"

I wonder if he means new automobiles being built or of all cars on the road in 98, only %10 were peak and hold. But it sounds like most folks can make use of it, but I would like to find a generic fix for the %10 peak and hold crowd.

dcb 01-23-2009 03:14 PM

It appears Coyote has a workaround so will close this thread,
Please discuss here as appropriate.

Less than 10% of vehicles affected, though that number may be higher in an ECOnomy crowd.


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