confirm before megasquirt

[bahelion89]

first off i hate posting vids, i always sound like a tool, and dont know whats going on..plus i seem to run out of words. that being said...

 

1975 280z 5spd swap, headers, newer motor...all done before i bought it. i've been chasing electrical and have finally said screw it and going megasquirt 2 with v3.0 board.

 

confirm bad AFM?

 

first video: i have the afm unplugged and in default it runs fairly well, the idle varies slightly it will sit at 900rpms if it runs for a while(wish it would all the time) but the purpose of this is to show that everything runs fairly well.

 

 

second video: plugged the afm back in. if it does decide to stay running it idles at about 500rpm. any time you touch the throttle it backfires or dies. like i said one of the guys on atlanticz has a way to reset the afm and it still didnt help. no matter what i do with the afm plugged in it doesnt run right.

 

 

let the trolling and comments begin!

[dexter72]

So does the engine run any better when you move the afm lever??..   Does the engine run better / no change, or worse when you move the afm plug??..

 

Is the afm harness plug green and corroded??..   Is the afm end green and corroded???.

[bahelion89]

guess i should have added that...I've cleaned just about every connection i can think of, replaced just about every hose, etc... pretty much everything that's recommended when you buy a z car.

 

if i play with the afm i can get the car to run the same as in default mode aka stupid rich. at that point the spring pressure is none existent. I've also run a bunch of electrical test showing everything is fine. That's why i'm going with megasquirt. its finally just caused enough irritation that i'm saying screw it.

 

the car was suppose to be my daily driver. but that just seems to be my luck

[z-ya]

Megasquirt is not a drop in replacement. You will need to make a new harness, and then spend a lot of time tuning the MS. If the engine is stock, then I would stick with the stock EFI. You may need to pull the harness, peel back all the tape, and look at all wires and connectors. ECUs are plentiful, so pickup a spare and try that as well.

[BluDestiny]

Whats your fuel pressure at?

[NewZed]

Your video shows that you're running very rich.  The engine revs with the AFM disconnected because there's extra fuel for the extra air you add when you open the throttle.  Going from rich to leaner.  When you connect the AFM you're adding fuel on top of the already-too-much-fuel so it floods out.  It's all described in detail in the usual factory issued document.

 

As far as the AFM tuning procedure with the pop can.  You'll notice that there is no background given at all on why that should work.  It looks neat-o but where did it come from?  Not Japan.

 

You should set your AFM back to where you started (you marked the spring position, of course) and start testing, again.  What coolant temperature sensor resistance did you measure before you started tweaking the AFM?  Megasquirt won't be easier, there are many threads like this one out there but with "MS" in place of "factory junk electronics".  

[BallZ]

I had this same issue...found a huge vacuum leak on the intake. unmetered air can cause your problem

[bahelion89]

Z-YA: i realize megasquirt is not just a drop in deal, and i'm prepared to do the electrical/fab work needed. i live in az so my electronics are not in the best shape due to extreme temps and everyone complains that its the supporting systems that make the l28 fail. 

 

BLUDESTINY: my fuel pressure checks out in the normal range. its one of the first things i checked after rewiring my fuel pump.

 

NewZed: Thank you for the better explanation. any idea what be causing the rich mixture? i've tested injectors, fuel pressure, spark...just about anything i could think of and what was recommended in the EFI Bible. its true about the pop can concept, but multiple people have used it with sucess and even a local specicality shop made the recommendation. The coolant temp sensor and thermostat are brand new, that was something replaced first..the car sat for several years before i bought it.

 

As for my plans, I'm sticking with the l28 (to me its part of what makes it a 280z), it will be a good first step as i will be swapping in a pallnet fuel rail, and using ls/suburban coils, down the line. Using MS gives me an excuse to upgrade all the supporting electronics.

[BallZ]

YOU MAY HAVE EXCESS AIR ENTERING THE INTAKE SOMEWHERE!!! Connect your AFM, have a friend start the car, you manipulate the AFM by hand it should run but you will have lean back fires. The same thing happened to me at first I was thinking that when I replaced my intake/exhaust gasket that I screwed it up. After trying the procedure I listed above, low and behold I missed a huge vacuum port that was hiding between the 5th and 6th runner. Also You can take the time to spray carb cleaner around your intake manifold and listen for changes in your idle...Ryan

[Swervey McZCar]

Disconnect connector and pinch the hose going to the cold start injector to see if the rich condition goes bye-bye.

[NewZed]

 i've tested injectors, fuel pressure, spark...just about anything i could think of and what was recommended in the EFI Bible. 

What was the resistance on the coolant temperature circuit, measured at the ECU connector?  Compare that number to the chart of resistance v. temperature.  Page 79 in the 1980 book, 54 in the early one.  

[NewZed]

1975 280z 5spd swap, headers, newer motor...all done before i bought it.

This is a big flag also.  You should go through the various components and make sure they're the right ones for the 1975 system.  It's not uncommon for people to install turbo injectors because they think they'll add turbo power.  Check that someone hasn't tweaked the AFM.  Check cam timing.  What were the numbers for fuel pressure?  Is the regulator's vacuum hose connected?  Etc.

[superlen]

Swervy and NewZed both have good suggestions.

 

If the coldstart valve is leaking, or electrically malfunctioning and just spraying you will get obviously get a rich condition, and the coolant sensor is prone to crappy connections & it will cause a rich condition as well. You said you cleaned all the connections so hopefully that's not biting you. Pinching the fuel line feeding the CSV rules this out in just a few minutes.

 

If it's not the CSV, then the only other thing that can cause the rich condition is the injectors spraying more fuel than needed and there are several possibilities there. Here's a quick list:

 

1. Fuel pressure to high. The stock ECU expects 36psi across the injectors. If your fuel pressure regulator is failing & you now have 42... well you're going to run rich.

2. The injectors are larger than 180cc/min. NewZed touched on this. If someone "upgraded" to larger injectors, again the stock ECU has no clue about this.

 

Assuming your PSI & injectors are correct, then it's the ECU telling it squirt too long...why? Well, i'ts reading the sensors & making a calculation. If one(or more) of these sensors are faulty, you'll have issues. So how do we tell? With the stock ECU, sadly the only method to do this is to make measurements at the ECU connector with a voltmeter and compare to the values in the FSM. I got annoyed at having to do this and designed a digital ECU drop in (HellFire). I can read my sensors with my laptop. It won't be availalbe until late spring so for now, you'll still have to do the FSM test. Here are the sensors that can fail and make you run rich.

 

1. AFM This is the #1 control element to set the amount of fuel. More air -> More vane movement -> more voltage to ECU -> more fuel. The AFM was a great idea in 1975 & it can work well if it's in great shape (although it's restrictive as hell). Sadly, most have drifited all over the place & who knows what you're really getting. Additionally, the wiper inside can become intermittant and have dead spots. It's important to get a nice smooth voltage without seeing spikes/dips when testing these.

 

2. CLT sensor. The next biggest contributer to calculating the fuel pulse width is the coolant sensor. If the engine is cold, the ECU dumps more fuel until the engine warms up. You wouldn't think it was much, but it can actually be a massive amount if the ECU thinks it's really cold. This is where those crappy electrical gremlins cause problems. Unhooking the CLT sensor or a high resistance connection due to corrosioin will make the sensor read colder...sometimes really cold. The ECU responds with dumping extra fuel. When you test this circuit, make sure you test right at the ECU connector. That covers your wiring all the way from the sensor to the ECU.

 

3. IAT sensor. The intake air temperature will also control the pulse width, but much less so than the CLT. Cold air is more dense so it contains more oxygen and thus we can squirt a little more fuel. So if this sensor is reading wrong, you could get a rich condition as well. The IATs on the zcar are pretty reliable however, & with the conditions you describe I would check it just to rule it out, but I don't think it's your problem. Note: when you unplug your AFM you are unplugging the IAT at the same time. So teh ECU now sees the following: AFM is a really low number so meter way less fuel, IAT has went to extremely cold (meter more fuel).. Who knows what percentages each of these are, but I'm pretty sure the net result would be to lean the overal mixture. That matches what you saw I believe.

 

The ECU it'self could also be failing. They are almost 40years old now. It's a wonder they still run. While designing the HellFire board, I've taken apart several of these. I'm amazed at well the Bosch engineers could implement the basic fueling requirments with opamps and multi-stable vibrators. Features and special conditions are easy to add with software, but when you're doing it all with analog parts that can/do drift with time/temerature, that's impressive. Apparently, the cold start feature couldn't be done with the technology they had or at least in the time frame they had so we ended up with 5lbs of wires, hoses, cold start valves, fuel lines and such on the intake.

 

Hope the above is helpful. A spare ECU and/or AFM to swap in/out of your car would go a long way for troubleshooting. PM me if you have trouble coming up with one, particularly an ECU. I have a few known good ones (or at least goodish) that I don't mind trading for even an known bad ECU. I can still use the bad ecu as a core for HellFire as long as the case/connector isn't trashed.

 

BTW, my gut instinct for your problem is your AFM(edit- i re-read where you tested the AFM - so I'd now guess ECU), at least if you have confirmed that the CLT sensor reading at the ECU is within spec & it sounds like you covered your bases pretty good there.

 

Also adding a fuel rail (like you were planning) with the FPR at the end (not in the middle) along with boosting the fuel pressure from 36 to 42 should help hot starts a lot there in AZ.....plus they look cool.

 

Lenny

Edited February 14, 2014 by superlen

[cgsheen]

I have the stock AFM, ECU, and injectors from my Son Nick's '76 L28E.  If you're ever near the shop, stop by and grab them.  Hit me up first and I'll make sure they're all in one place.  If any of them work for you, you can tell me what it's worth...

[z-ya]

Check the hose between the AFM and the TB for cracks.