MSefi.com read only forum (Jan.15,2018)

I installed larger injectors that I pulled off of a car at the junkyard and now the AFR goes way lean in cycles. When I added the injectors the only thing I did was calculate a new required fuel based on the new injectors. I assumed that if I got the required fuel correct then I would not need to change warmup enrichments or the VE table. Is that a correct assumption? Im guessing that the injectors may be a little clogged, I don't know how long they were sitting in the junkyard. Is there any other settings I need to change in megatune to run the larger injectors? Or should I assume its the clogged injectors.

Old Injectors Bosch Blue Top 24 lb/hr @ 3 bar .. (Req fuel 13.2)
Bigger Injectors Bosch Red Top 33.3 lb/hr @ 3bar (Req Fuel 9.6) Bosch 0 280 150 431

1985 Saab 900, MSII v3 code 2.883 Megatune 2.25. Controlling Fuel and Spark

I did some more testing and the problems are mostly at idle and low map pressure. It bucks or surges because the AFR is going lean and rich. I tried adjusting the injector opening time and VE table. I noticed that it would only idle smoothly at a much richer AFR. With the old injectors it could idle smoothly at a 16.5 AFR. The impedance on the injectors is around 12 ohms. I put some Lucas injector cleaner in the tank to see if that sorts it out. I only paid $5 for the injectors at the junkyard so its not a big deal if they don't work, but I don't want to run my old injectors too much because I was seeing well over 100% duty cycle on them regularly. I think I will try and find another set of injectors at the junkyard.

Just a thought to add :

Check the required Fuel pressure that the kit you had ran vs the new injectors need, on the model car you removed them from I had this prob on mine when I was injector playing

Nige

RS68 wrote:I did some more testing and the problems are mostly at idle and low map pressure. It bucks or surges because the AFR is going lean and rich. I tried adjusting the injector opening time and VE table. I noticed that it would only idle smoothly at a much richer AFR. With the old injectors it could idle smoothly at a 16.5 AFR. The impedance on the injectors is around 12 ohms. I put some Lucas injector cleaner in the tank to see if that sorts it out. I only paid $5 for the injectors at the junkyard so its not a big deal if they don't work, but I don't want to run my old injectors too much because I was seeing well over 100% duty cycle on them regularly. I think I will try and find another set of injectors at the junkyard.

Injector spray pattern problems would be most evident at Idle/low MAP conditions and the partial misfires that would result would show up as varying amounts of O2 in the exhaust stream which the AFR gauge would read as varying AFR.

I think before you continue tuning you should have those injectors checked out so you don't chase your own behind in circles.

I solved this problem a month or two ago. I was running 4 squirts alternating and went from 24lb injectors to 33 lb injectors. This dropped my lower fuel req from 6.6 to 4.8. The new lower fuel req put my idle and cruise pulsewidths to around 1.7ms which was too short for the injectors to spray properly. I changed to 1 squirt simultaneous and this put my fuel req to 9.6 and solved the problem.