I am swapping in a '7727 ECM into a '93 V6 Camaro and am unsure of the wiring swap to convert to batch fire.

The injector drivers in the '7727 is pin D3 for 1,3,5 D4 ground and D9 for 2,4,6 D12 ground. The ECM it's replacing has C12 inj3, C13 inj2, C14 inj1, C15 inj6, C16 inj5, C32 inj4. C1 and C17 are the grounds.

Is it OK for me to just run the C12, C14, C16 (parallel) on the harness to D3 on the '7727 and C13, C15, C32 (parallel) on the harness to D9 on the '7727 and the appropriate grounds, or should this be a series-circuit?


Also...

The Camaro ECM has a high pressure A/C switch and it appears that the '7727 can control this with pin C21, but am unsure if the A/C system in the Camaro also needs evap can signal for some reason, and don't see a way with the '7727 to use said signal. Any thoughts? What masks use this A/C setup?

Thanks,

-John


EDIT: Sorry the ECM being replaced by the '7727 is the 16172693 flash-only OBD1, and the transmission is the 4l60 non-e. I can post the pinouts for both ECM's if needed.

 

Sorry. A little more research and I found the answer to the batch vs sequential question, but I still am curious about the A/C situation.

 

I was able to get the ECM temporarily in place. I tinned the wire ends with a soldering iron and shoved the tips into the stock connectors to make it easy if there was something out of place.

Here is the very first start up. It sounds bad because I missed the MAP sensor wire, but once I got that connected it ran OK. I used the stock $a1 code/chip (from a FWD Lumina '7727 ECM), so I gather that's why the idle was high, and I may have the fan wire in the wron position, because it never turned on and started to over heat - might need to be on the secondary fan pin instead of primary, but I guess I will have to look at the .bin on the chip to see for sure (or get input from you guys )...




Here's the spaghetti mess I started with...



and during the "swap"...





Not that alot of this means anything to you guys, in the end I guess I just wanted you to see what I was going through to get here :jest:

Next I will pull the pins out of the '7727 connectors and solder in the wires directly from the car harness and iron out the bugs.

One other thing I have to iron out is the difference in the way the A/C turns on. The "older" ECM's only had a request signal and a clutch control. The F-body (OBD1.5?) uses a different turn on function than the more common OBD1 ECM's. Any thoughts on how I can overcome this to get the A/C to work properly?

My datalog cable took a dump on me, so I couldn't datalog this first startup, but the new one should be here any day.

 

Well, it's rich as expected, due to injector size and different firing scheme now.

Idle being high is common with $A1 and first starts, until the ECM trims fuel and "learns" idle.

So the A/C didn't work at all with the '7727 ECM connected?

 

Idle was about 2200RPM, and I'm guessing that the stock ECM was $A1, but I will pull the chip after dinner and read it to be sure.

No A/C. I moved a wire from an unused pin to the "A/C fridge pressure signal" on the '7727, so perhaps that's not a function of the code mask? There is also a "A/C evaporator temp sensor signal" and "A/C status" that I left blank on the harness because there was no provision for those on the '7727, so I am at a loss on the A/C situation.

The only other bug so far is the fan not coming on at operating temp, and of course it heated up rather quickly with the high idle, so I shut down for the time being.

On top of that, there is no "voltage check" column on the pinout I have for the '93 ECM to make heads or tails of the extra A/C wires

 

Confirmed it as $A1.

Six, not sure what you mean by different firing scheme? This is a 3.4 with DIS and the injectors are actually the same as a 3100. The rich condition in the video was due to the lack of MAP sensor (also the reason for the SES light). Once I plugged the MAP in on the second start, it ran good except the high idle, A/C not working and the fan not coming on.

 

Two diffefiring shcemes:

One is batch fire, the other is sequential.

 

I wired the injectors to be batch fire. It was my understaiding that the '7727 is batch fire and wired the injectors three to a driver like they would be in a MPFI car. Did I do something wrong?

 

*sigh*

John;
What I'm saying is you wired a car originally set-up with SFI for batch fire. This will usually cause a rich condition without tuning the batch fire ECM, due to the fact that SFI engines usually have larger injectors for the same displacement than MPFI engines use. Since MPFI ECMs will usually fire the same injector twice as often as an SFI injector, or even more often, this will usually deliver an excess of fuel causing a rich condition.

 

i was just going over a 93lt1 repin tonight. and found a thread about the cooling fans being mislabeled on some diagrams.

if you have your fan on A3 now, try moving it to A9.

as for the ac. i looked at it a bit too, and am not sure just looking at the pin outs. because it seems like they are totally different setup systems. the only ones, at least the $8d is a simple cycling kind and the newer 93 has evap temp sensors and all kinds of stuff. then sometime they went to a variable displacement compressor. so your going to have to find out what you have. and you may have to wire in some relays to handle things that they ecm used too.

 

Thanks. I have the fan on the A9 pin of the '7727, the pinout diagram I have says this is primary cooling fan and A3 is secondary. I will probably swap it over and see, I imagine ONE of them will have to work.

Come to find out the A/C systems aren't that far off. I have an inclination that using the pressure switch from an older system might work. Hook it up to the '7727 and the ECM SHOULD kick the clutch on/off accordingly. I'm hoping the 2 sensors are interchangeable, but I'm sure it won't be that easy Gonna find out later tonight when I get a look at it.

Apparently the evap temp is to shut down the clutch when the evap reaches 32*. Status monitors the voltage going to the clutch. High pressure sensor stops the clutch if the system is high/low on freon. The relay is the same as in an older system, and the request is also still 12v.

The only drawback I can see is that the system will be higher temps than it would with an r12 system due the the pressure/temp differenced between r134 and r12.

 

You can test the fan outputs by setting a low temp, and watching the fan or fan status then. You could also test by using resistors or proper valued rheostat to the CTS input and test the fan turn on temps that way.

 

Well, the A/C sensor swap went as planned....

The older system has a 1/4NPT fitting and the '93 has some weird thread (probably proprietary). I think if I thread the '93 with a die to match it will work, but I will have to measure the major and minor diameters before thinking about that. We don't want any leaks haha.

Got the new USB cable from Moates today and am trying to get that sorted out. Having trouble connecting, even after following all the procedures. I can get cable verification in both ALDL_Test and TunerProRT, but won't connect to log. Just loaded a known good .bin/.ads combo ($59) and will try that.

Thanks, Chris will try that once I get the thing connected.

Once I'm all hooked up, will start pulling the '7727 pins and wiring the ECM properly.

 

OK. The ALDL with a known good mask/bin is good

Now why can't I log the stock chip

Next step I guess is go ahead and get the ECM hardwired in, and burn a fresh $a1 bin, but I don't know why it's not working. I'm not stuck on the $a1, but it is a mask that us V6 guys have been running for the aluminum heads and seems to work well. Any suggestions?


Anyone else have a problem with $a1 and TunerProRT?

 

Got the ECM hard wired in, burned a $A1 mask chip, and was able to connect to the laptop fine now. Only thing I can think is that perhaps there was a V8 chip, or bad PROM in the 2 ECM's I had. I put another known good knock circuit section on my adapter and it is reading/running good - best so far actually.

I am still having a couple flags (error codes). One being coolant temp too low, open loop (or o2 absent), and checksum (PROM error).

The o2 sensor may because I hooked up only one sensor (OBD1 uses 1 o2 vs the two in the car previously) and may have reversed the ground and am actually hooked up to the signal side of one o2 and the ground on the other lol. Could be a bad o2, or may be having problems with the rich tune in there now.

Temp being too low may be because for some reason the coolant fan kick-on temp was set at 107* and the iron heads like to run much hotter than that. The only other thing I can think of is maybe there is a difference in the temp sensors themselves, but I have examined the 3.4 and 3.1 sensors and they appear to be identical (maybe someone can verify?).

Not sure what to make of the PROM error unless maybe there is a wire I left off that needs to be hooked up to sum correctly. The '7727 ECM has two 5v out's for the sensors and the stock '93 f-body ECM had only one for all the sensors, and a matching ground. Might have to pair the 5v out with the other and send the loose ground to ground.


Start today. Running rich as mentioned, checking for codes, making sure all the sensors were working, along with fan etc. All good except after warmup (as I mentioned the codes above)...



Started installing the wires one at a time. At first I started pulling the pins off the wires, but it took like 20 mins to get the first one done and decided to solder/heatshrink the pigtails from the ECM instead...

 

for the r12 to 134a convert. 134a needs a much lower psi on the low side to get the same temp. I can't remember the numbers but it we like 32psi was 32* for r12. 134a 20psi is 32*. so if you have a cycling type of ac setup. you need to adjust the low side switch down to 20psi to get the same temps. that and use about 70% of the charge called for with r12. you should be able to get a solid 40* vent temps on recycled air max ac if done right. if you have a verable displacement compressor you will need to change out the control valve in the side to a 134a pressure. as for the o2. maybe check that the heater is working. and you should be able to check the 0-1v output with a normal volt metter to see if the sensor is lighing off. but if its super rich you may have to get it leaned up before the sensor will work.

 

Yeah. After looking around a lot more I realized how the newer 134a setup acts. Basically the ECM controls the on/off function, but it's rather simple. The pressure sensor switch is 0-450psi and will send from .1-.49v. I was talking to a gentleman tonight about his A/C on his MeagSquirted 4th gen who wanted to separate the A/C from his car's ECM so he could be full stand alone. He actually tried a potentiometer and a small circuit to the A/C system and it would just click on and off rather quickly. We kind of put our heads together and have come up with a scenario, but not sure how to impliment it. We need the compressor to shut off somewhere around .5 volt and 4.5 volt, and to be on (matching A/C request) otherwise.


I also wondered about the o2 not being active because the rich condition might keep it too cool. That and the fan on was low, so I dont think the car ever really warmed up properly. Probably should have saved the log to make sure, but the storm was coming and had the easy-up tent out and had to hurry to break it down before the rain. I was just happy it seems to be going well and this might be a really rewarding project

I read this really great article explaining how the different refrigerants react to pressures...

http://www.autofrost.com/autodisc.pdf

 

PROM error is all internal in the ECM. The ECM also won't know that you are only using one of the 5V ref outputs, it doesn't care.

Check the grounds for the sensors, that might be the issue with the sensors reading low or wrong.

 

Well, I burned a new chip using the tables from the $88 iron head v6 tune (stock). I wanted to use the $88 mask all together to make things easy, but there was no cyl offset in the definition so adjust for the 59* offset in DIS, so $a1 was used.

The car started and ran much better, no more black smoke

BUT! Still had the o2 and MAP flags, so I went back over the wiring diagram. Even though the 5V+ shouldn't matter, it did. I moved pin C12 (5V+ ref) to C7 and the MAP issue went away. Then I was curious if the ECM would like to see the sensor grounds in the correct place. The pinout diagram I had didn't specify what grounds were what, so I cross referenced with a '9396 ECM (similar to the '7727 with a couple diff pins) and saw that A22 was actually meant for the o2, so I swapped A22 with C5, and what do you know! Works great now.

I didn't like the lower idle of the 3.1 tune (~750-800) since the cam in the 3.4 seems to like an idle of about 950-1000 - or it sounded cammed and would like to bog when the wheel was turned or the brake pedal depressed, so I bumped it up to 950.

A little later when it starts getting dark, I will post a pin swap guide with the new changes for future reference.

As far as the A/C goes, I was chatting with a GM rep at Scoggin Dickey and he explained to me how ALL the GM A/C systems run off the low side sensor and he just go done doing an LS swap in a truck using the new A/C system and OBD1 ECM. He told me if I ground the compressor clutch relay through the low side sensor, then the system will kick on/off like it should independent of the ECM, so that is next on the agenda.

 

make sure you have a hi side cutout wired into that too. just incase a cooling fan doesn't come on or something. things could get ugly.

in case your system doesn't have a port on the high side for a fan turn on. i ran across a switch called a Trinary Switch, it has a high psi compressor cut out(380psi) and a high side fan turn on(220psi i think) keeps the fans from running on high when not needed, like say highway trips.

just throwing that out there.

on and i believe the lt1 years had a evap temp switch to cycle the comp too so it doesn't freeze up. but if you adjust the low side cycle switch to around 25psi you shouldn't have that prob anyways.

good to see you got it working.