Multec1 vs Multec2 injectors.

[burn]

So as some may know I currently make a chip to run the 3400 in a J-body with the 00+ FPR & multec2 injectors. So here is where it gets interesting.

Well a guy I know through the boards runnin a 3400 in a 90 Z24 with 5L mustang injectors, 99FPR & stock 3.1L PROM wanted to swap to the multec2 injectors, 00+ FPR & my custom chip. He drove the car without any problems from his house in Windsor to my house in Sarnia (100km's+)

Naturally curiosity got the better of us and we were thinking that since his mustang multec1 injectors, and the 00+ multec2 injectors are both about 19# that if we swap to the 00+FPR & my chip that it would run with his existing 5L injectors. Well, it wouldnt. It wouldn't even make an attempt to start. After changing the injectors I had Rob turn the key to 'ON' and 'OFF' a few times to build fuel pressure after having replaced the FPR. When we replaced the FPR we didnt remove / unhook anything. not even remove the TB. Absolutely nothing other than the FPR & chip had been touched since he drove to car to my house.

So then after unsuccessfully starting the car, we swap out the 5L multec1 injectors for the 00+ multec2 injectors. After re-assembling the UIM, and repeating the same 'ON' 'OFF' procedure as previously, within a fraction of a second of the key being in the 'START' position it fired right up without any hesitation.

The no-start with the 00+FPR & my chip while still on the old 5L injectors could NOT have been a poor-connection problem with either the chip or FPR as we didnt touch them during swapping to the multec2 injectors.

Now after we took it for a rip and were happy with the results he was on his way. Well a few weeks later we get thinking about why it wouldnt start with 19# multec1 injectors, but it would start with 19# multec2 injectors. This situation has us both completely stumped, as well as others on V6Z24.


The only possible theory that I can think of is that: could it be possible that the multec2 injectors are capable of opening and closing faster than the multec1 injectors. The BPC I have assigned to the multec2 injectors is significantly shorter than the stock multec1's. Perhaps by the time the multec1's receive the signal, and charges the coil to open the injector, the signal goes back to 0 and closes. They are simply are not capable of opening and closing in the time duration set-out for the multec2's to operate at. Instead they simply sit static closed. The reason I came to this possibility is based soley on the physical size of the injectors. clearly the multec1's are significantly larger, and perhaps use a larger / more power hungry coil to operate at, than the much slimmer multec2 injectors.

I dont know if this is accurate or not, its simply speculation. I have no idea otherwise why the multec1's wouldnt work.

Anyone have any insight to this?

[burn]

NE1?

[ryan.hess]

Too long. Give me a 1 sentence summary. :P

Engine doesn't start/run on 1 set of injectors, does on another? Were FPRs switched? Is it possible one FPR won't work with one set of injectors due to different pressures? Some injectors are sensitive with higher pressures than "rated", they'll lock up on you and not even open.

[burn]

Too long. Give me a 1 sentence summary. :P

Engine doesn't start/run on 1 set of injectors, does on another? Were FPRs switched? Is it possible one FPR won't work with one set of injectors due to different pressures? Some injectors are sensitive with higher pressures than "rated", they'll lock up on you and not even open.

Its more that engine wont run with 19# multec1 injectors and my chip, but will with 19# multec2 and my chip.

The FPR is not the issue because he ran the 19# multec1 on the 00+ FPR before and it just ran really rich.

[treeZ24]

i kinda agree with your theory there burn, although i dont know for sure, what the times needed to open the injectors are i'm sure you can find them.

one thing to consider which supports your theory is that the mustang injectors are quite a bit heavier then the stock multec2's, so possibly the internals are again heavier and take more energy + time to move.

*shrugs*

[burn]

ryan.... your thoughts?

[discostu]

Do they run on the same impedance?
Would this even make any difference?

[ryan.hess]

I don't know... Do you have another set to test? I don't know what kind the northstar use, but they're absolutely terrible for leaking and not opening, even low mileage ones. All you need are 3 to stick closed (not impossible) and it won't run.

Did you use the original multec 1 FPR with the multec 1's?

[burn]

We tested various difference configurations, and the setups goes as follows:

- multec1 FPR + 5L multec1 injectors + 3.1L PROM : ran slightly rich, but ran good enough
- multec2 FPR + 5L multec1 injectors + 3.1L PROM : ran excesseively rich, but still ran
- multec2 FPR + 5L multec1 injectors + 3400 PROM : would not run at all
- multec2 FPR + multec2 injectors + 3400 PROM : runs like a champ


Also, these setups verify that both FPRs, both sets of injectors, and both PROMs are all in good working order.

[ryan.hess]

- multec2 FPR + 5L multec1 injectors + 3.1L PROM : ran excesseively rich, but still ran
- multec2 FPR + 5L multec1 injectors + 3400 PROM : would not run at all

Well the two FPRs are obviously set to different pressures. The multec 2 is set to a higher pressure than the 1. Also, even though two sets of injectors are rated the same, that doesnt necessarily mean that they are rated at the same pressures. Your 19# multec2s could be rated 19# at 51.3psi while the 19# multec1s could be rated at 45 psi.

So, when you swap in the multec1 injectors, with the multec2 fpr, you now have an effective injector rating of 20.2#/hr injectors. This will run with the 3.1 prom, but swap on a 3.4 prom which will try to force even more fuel in, and it won't run at all because you're flooding the motor.

...my 2 cents from what I understand about your situation

[sharkey]

correct me if im wrong, but i thought all gm injectors were rated at 43.5psi and all ford injectors were rated at 39psi. i may be wrong on it, but i did read it somewere.

[ryan.hess]

They are not. One example - the LS1 injectors are 28#/hr. But they're rated at 60psi. At 45psi, the "norm", they're only 24#/hr.

[burn]

- multec2 FPR + 5L multec1 injectors + 3.1L PROM : ran excesseively rich, but still ran
- multec2 FPR + 5L multec1 injectors + 3400 PROM : would not run at all

Well the two FPRs are obviously set to different pressures. The multec 2 is set to a higher pressure than the 1. Also, even though two sets of injectors are rated the same, that doesnt necessarily mean that they are rated at the same pressures. Your 19# multec2s could be rated 19# at 51.3psi while the 19# multec1s could be rated at 45 psi.

So, when you swap in the multec1 injectors, with the multec2 fpr, you now have an effective injector rating of 20.2#/hr injectors. This will run with the 3.1 prom, but swap on a 3.4 prom which will try to force even more fuel in, and it won't run at all because you're flooding the motor.

...my 2 cents from what I understand about your situation

right, and there in lies the problem. The multec1s should run slightly richer than the multec2s at the same pressure. We already know that the multec1s will run on the 00+ FPR because he ran it like that for a while, so its not an issue that they cant handle the increased fuel pressure. My tuning for the 3400 PROM reduced fueling by around 40% over the stock 3.1L PROM. The larger injectors & higher psi FPR caused me to need to reduce fueling in order to properly fuel the larger engine.

[burn]

anyone?

[TurboGTU]

multecII have a faster opening rate (sensitive springs, responsive coil) than sluggish Multec Is. The Multec Is seem to have a stiffer spring and heavy internal body. THe MII take advantage of the SFI while the MI have to be a bit stiff because they all fire at the same time regarless of what engine cycle the cylinder is at. That valve will have a nice puddle behind it.

It takes more FET power to run the MultecsI at idle than the Multecs II.

22lbs Multec IIs seem to run excessivly rich on a stock 3.1ECM even if the ECM had 22lbs Multec I programmed. I think Ben had problems tunning them. I know some 3400 swap guys did and said they woun't work well on the MPFI ECMs.

My indector Duty cycle with 35lb GTP Multec IIs are about .29 at 700rpm to get it within 13.5-14:1 a/F ratio. After that...I had to mod the VE tables like Multec Is. Idle is a pain with thise multec IIs.

If you have them flowed at a shop..im sure you can get more flow out of the MII at light bpw than the same rate M1 . At 100% DC they are the same. Even at 20-90%. But under that...the MII deliver more.