Injector driver upgrading.

[Six_Shooter]

I am running a 1227749, and $59.

I seem to be running out of injector. Static RPM/Boost levels seem to be alright, but transients, such as going from low RPM/vacuum to higher RPM 15+ PSIG boost, I get a lean spike as it passes 7 PSIG or so. Slower building of boost reduces or eliminates the problem (opening the throttle slower, as opposed to mashing the pedal).

So I have a set of larger injectors, that I want to install, but they are low Z injectors, and according to information I have found I need to upgrade the injector drivers. http://home.comcast.net/~p-928/749mods.html I have the proper value of sense resistor, I've actually had them for a while now, but the MOFETS were already obsolete before I got the sense resistors.

I have found some information that suggests other MOSFETs to be used. I'll have to find the links again.

I have found a couple based on similar specs to the MOSFET speced in the link, but still need to find out about availability.
http://www.fairchildsemi.com/ds/FQ/FQB47P06.pdf
http://www.fairchildsemi.com/ds/FQ/FQP50N06.pdf

Has anyone found any specs on the original MOSFETs? I tried searching for the numbers that are printed on the MOSFETs without success.

I'm thinking about trying to use the larger injectors with just the sense resistor change, but the original MOSFETs. Anybody tried this, good/bad/other? I'll be changing from saturated injector control to Peak and Hold.

Thoughts?

[RobertISaar]

i don't think the FETs are going to be THAT critical in terms of specs, but since the original units seem to handle ~8 amps on a regular basis without failure, that's at least a starting point.

have a preferred supplier? if you want to "run the gauntlet" and try out a lot of different options, tayda electronics has a decent selection for some pretty good prices once you hit their $5 minimum order. shipping has generally been less than a week for me as well, since they seem to have a distributor somewhere in new jersey, IIRC(they're a thai company).

some documents from back in the day imply that the C3 injector drivers were LM1949 units. not sure if that applies to P4 as well? anyways, there are some datasheets out there for those.

EDIT: LM1949 are actually way different.

[RobertISaar]

HUF76429 = 44 amp, 60 volt N channel FET with a nice, low RDS(ON) spec(at 5V, drain to source resistance is only .025 ohms). at 4.5V, max turn-on time of 325nS, max turn-off time of 155nS.

for comparison/alternatives:

STP65NF06: 60 amp, 60 volt. at 5V GS, can allow 50 amps. at 10V GS, ~75nS turn-on time, ~56nS turn-off time typicals. $.41 each and seem to be better suited than the HUF76429 units?

IRFZ44: 49 amp, 55 volt. at 5V GS, can allow 20-30 amps... kind of low. jumps up to ~50 amps at ~5.75 volts. 10V GS, ~72nS turn-on, ~89nS turn-off. $.45, gate-source sensitivity is kind of offputting.

IRF540N: 33 amp, 100 volt. at 5V GS, ~30 amps... kind of low. ~50 amps at 5.5 volts. 10V GS, ~46nS turn-on, ~74nS turn-off. $.57, gate-source sensitivity offputting.

IRF3710: 57 amp, 100 volt. at 5V GS, ~45-55 amps. 10V GS, ~70nS turn-on, ~92nS turn-off. $.76, seem to be a good choice?

IRF3205: 110 amp, 55 volt. at 5V GS, 35-50 amps. 10V GS, ~115nS for turn-on and off. $.88, seem pretty good?

STP80NF55: 80 amp, 55 volt. at 5V GS, ~40 amps. 10V GS, ~110 and ~95nS for on/off. $1.03, seem pretty good?

IRF2807: 82 amp, 75 volt. at 5V GS, ~70 amps. 10V GS, ~77 and ~97nS for on/off. $1.10, seem pretty beefy.

IRF3415: 43 amp, 150 volt. at 5V GS, ~45 amps. 10V GS, ~67 and ~140 for on/off. $1.53, seem good.

RFP40N10: 40 amp, 100 volt. at 5V GS, ~30 amps. 10V GS, ~80 and ~100 for on/off. $1.75, good, but price seems high compared to others.


that's everything i found at a "glance"... seems that IR makes most of them. those STP65NF06 seem to be an excellent deal?

[Six_Shooter]

That's what I was going to end up doing and just going through other MOSFETs looking at their specs and compared to the HUF76429

I spent some time on the IR website last night trying to find a datasheet for the original MOSFETs, but have come up empty handed so far. I might have to contact them and see if they can help me that way.

[1project2many]

By original, are you asking about the GM devices or the ones listed on the upgrade page? IIRC the Cherry Semi 452 / 453 were being used as replacements in the very early days.
This is the Fairchild Semi part on the upgrade page:
http://pdf1.alldatasheet.com/datashe...FA76429P3.html


Don't forget that your semiconductor life will depend on proper heat control. The 7749 in the Cavalier would get very, very warm on 1hr or longer drives thanks to the four TBI injectors I was using. I really think it could have benefited from a 12V fan or some finned aluminum attached to the case. I never had a failure in the years it was in service, but still... if your ecm is in an area with little airflow this might be worth remembering.

Also, with the additional current (and heat) you might want to look at your ecm/pcm for multiple current paths to the MOSFET. The pins and traces are small and there are stories of upgraded drivers plus six injectors resulting in fried boards.

[Six_Shooter]

Yeah, I've been thinking about adding a fan, and possibly upgrading the heat sink.

[socrace]

I am running a 1227749, and $59.

I seem to be running out of injector. Static RPM/Boost levels seem to be alright, but transients, such as going from low RPM/vacuum to higher RPM 15+ PSIG boost, I get a lean spike as it passes 7 PSIG or so. Slower building of boost reduces or eliminates the problem (opening the throttle slower, as opposed to mashing the pedal).

Thoughts?

Just wondering, if injectors deliver adequate fuel under full boost, why larger injectors? Looks like maybe fuel pressure lag is causing the temporary leanout?