I have had it with the OE ECM and all the issues. I want to install a microsquirt fuel injection controller. The instructions seem very straight forward but I also want to keep as much as possible from the current dashboard. First has anyone tried this conversion? Where do the inputs to the dash come from? Do they come from the OE ECM?

 

I've got a Holley HP in my 85. You will lose the MPG and fuel range features on the dash since they are controlled by the computer but the rest of the gauges are run from the sensors. Even the cruise control will still work since it is controlled by the dash.
If you do decide to ditch the factory EFI, don't throw the ECM, MAF, or burn off module away. They are all one year parts, specific to the 85. You shouldn't have any trouble selling them.

 

Thanks, I am not familiar with the burn off module. Also did you keep the ECM wired and in place and just switch out the motor sensors and run them to the Holley? My other idea is to add sensors that get wired as inputs to the new controller and disconnect the outputs such as HEI and injectors.

 

I also have a question about the engine's cold idle control. I don't see any fast idle solenoid or stepper motor. I can program in some additional timing when the engine is cold. Is that how the OE controller adjust cold idle?

 

The factory ECM goes away. No need to run any sensors to the old one.
For the dash: the factory speedometer, coolant temperature, oil pressure, and oil temperature senders stay wired as-is. You will use the factory senders to run the dash. My tach feed comes from the Holley EFI.
I am not familiar with the Megasquirt but the wiring will be similar with any aftermarket EFI.
I only had to add two sensors when i switched to the Holley system. It has another coolant temperature sender of its own and came with a new MAP sender. It also controls the factory IAC motor, which controls idle RPM. (Yours has one, it's on the bottom of the throttle body.)
Are you planning on running the factory HEI ignition or something aftermarket? I believe you can keep the factory HEI if you aren't planning on making it a sequential EFI system.
The switch to an aftermarket EFI system can be a little tedious (wiring it takes time and attention to detail) but isn't too terribly difficult. If you run in to any issues with wiring it, I'm willing to help as best I can.

If I remember correctly, the burn off module is behind the "bread box" in the 85.

 

Megasquirt will work just fine with the IAC valve you already have, no need to control idle with timing.

The only sensor you'll need to change out will be the MAF, I don't believe megasquirt will work with a hot wire MAF. You can either go to a MAP sensor or put in a different MAF.

 

For twice the cost of the microsquirt you can get the Holley terminator x with harness. Much better software, user friendly and capable of sequential injection, as well as coil near plug ignition. These two features if tuned right on a tpi engine will result in some more average power, as well as better cold start, drivability etc. The microsquirt is actually a step backwards from the maf system your 85 has. If it isn't running right and is stock you have mechanical or electrical issues. If you can handle the microsquirt install you should have zero trouble reading the fsm and troubleshooting the car. An efi system isn't going to be a magic bullet, and for a basically stock engine and car will not offer much more.

 

What issues? It's a good system, if you can install and tune an inferior megasquirt then you shouldn't have any issues with using the factory service manual to get your 85 running and driving right. The big reason to go stand alone efi is cam choice that is next to impossible to get to idle and start in closed loop. I'd hate to see you hack job the car, put an inferior batch fire speed density based ecu in place, lose fuel economy display and fuel range display just because you are having trouble fixing it.. what "issues" are you having that you can't get sorted out.

 

I had no idea the Megasquirt was so expensive!
I agree, the Terminator X would be a better route. Looks like the 550-936 might be a good fit and cheaper. ($1249)
I haven't used the Terminator X software but have used the HP/Dominator software and it is pretty user friendly.

 

The microsquirt comes with ecu, and unterminated flying lead. Costs $400 with tax and shipping, you'll hack the cars wiring vs removing the engine harness. And have much more limited fuel and ignition tables compared to stock. It's not junk, but it has limitations and compared to the maf system in the 85 it is inferior in just about every way. If I'm not mistaken it doesn't have a driver for iac, nor an output for fuel pump relay etc. It's a good ecu to use on a bike, very small. Doesn't have built in wideband, so by the time you buy one you'll have 8-900 invested. It has no internal data logging capabilities either. Simply put; it isn't a good choice for a daily driver c4! Some of the megasquirt stuff is much better, but not cheap. The terminator x universal kits are around 12-1300 last I checked. It's software is basically identical to the HP dominator stuff. For the price it's amazing how much you actually get with the Holley terminator x.

 

I only looked quickly at the Megasquirt stuff, mostly MS2 & MS3. Those ones are pretty expensive.
The TermX is a pretty good value. I went with the HP in my 85 (turbocharged) but would have gone with the TermX Max for my 99 Suburban instead of HPTuners if it had been released back when I did upgrades to the truck.

 

I would not recommend touching micro or megasquirt unless you are already extremely familiar with stand-alone tuning and setup details such as wiring and grounding strategy, shielding and diagnostics.

A holley with harness is superior for beginners, easier to make fewer mistakes. But still there are plenty of mistakes to make. I find many people tying their harness wires together with starter wires and battery feed cables for other devices. You have to really know what you are doing mechanically and read the manual if you are new especially.

 

Thanks all for your responses. Here is were I'm at. The car is a completely stock car and blows EST and EGR codes randomly. I have replaced the Knock sensor, 2 EST modules, one ECM , ignition module, O2 sensor and it still has the same issues. It hasn't even changed a single thing. I can buy a Microsquirt from DIYAutotune with harness for under $400. I have already spent that much to get try to make the car run decent. Yes the controls for the Microsquirt might be inferior but it should run and I can play with the fuel table until my car runs decent.

 

All computers work the same way. There is nothing wrong with the controls , the ECU are more than adequate. The product isn't poor or low quality, they are all very high quality products. Megasquirt is perfectly viable.

The problem is, if you have not already done it at least three or four complete installations Inside various kinds of cars, you may make a series of avoidable mistakes which may be difficult to overcome without guidance. For example harness shielding and ECU grounding and power supply proximity. Wires carrying large currents produce magnetic fields which interfere with nearby wires. So a starter cable for example near the ECU or ECU harness is going to likely scramble several sensitive signals in the ECU- and the car might still try to start anyways, possibly causing damage to the engine. If very high compression an improper early timing event at cranking can be disastrous to bearings for example, it may create extremely high compression PSI While there is no oil pressure during cranking. Another thing common is the crank trigger signal issues abound, it seems like every other vehicle that the customer does the install themselves and then asks me to tune has some issue with the crank trigger when using aftermarket computers especially. Another thing is that when the starter disengages the collapsing magnetic field causes a voltage spike. Even injectors do it. So proper use of diodes and power feed fabrication is a part of setting up to run right which can influence tuning and issues with burning up electronics over time.

 

That was my point, with no tuning experience, the lack of ability to datalog, and additional cost of a wideband kit he will be into it a grand before he even begins the install. And no offense intended to the op, but if he can't troubleshoot some codes and get it running right with the factory ECU.. jumping into a complex microsquirt install is not a good idea period. Especially the codes he is describing. He has already made the classic amateur mistake of throwing a bunch of parts at it that it didn't need, he would be better served buying a tech1 scanner and the factory service manual for his exact year make and model, sorting it out. By doing so he will get an education and better understanding of how efi works. Then down the road if he attempts to do an efi system swap he will be better equipped to deal with all the little things that will arise during the install and tuning process. I never said microsquirt was junk, I said it has limited features, and requires you to have fundamental efi knowledge that he clearly doesn't have. Not once has he indicated he actually put a scan tool capable of giving data, even the obd1 stuff had limited data displaying abilities. Not once has he mentioned having the gm published fsm and following the logical flow charts they give for troubleshooting the codes and conditions he says it has. So to suggest an entry level ecu that is designed for and aimed at 2-4 cylinder engine market, but can run a V8 is just bad advice anyway you slice it. It really Sounds like he'd be better served finding a semi retired mechanic that was a gm dealer master tech circa 1980-1996 that understands these cars, and can sort it out. They are out there, and we'll worth the 4-8 hours labor they charge to troubleshoot something like this. The stock maf system is actually pretty good, can handle decent camshafts and is in general a little more forgiving than the typical aftermarket speed density efi system. Plus it's already there, and the car does run and drive. You know as well as I do he probably has worn, frayed, damaged wiring, carbon in the egr system from years of pump gas, and possibly a host of other small issues. The microsquirt ecu manual is 150 pages. And is a very steep learning curve for even a guy that has tuning experience, because it has design limitations. It is not inferior, just engineered for a specific market, a daily driver street v8 car would be just about the most undesirable, impractical application for it. To suggest any aftermarket efi system is a valid plan at this point given the ops skill level is a recipe for disaster. He just needs a skilled professional to assist him and the car will be ok without rewiring half the car, or attempting to learn efi. Third gen.org tech sections would be a good place to do some more reading, the problem (s) he claims to have are not uncommon, and odds are someone has been there, done that so it would behoove him to do some research prior to diving into a efi install. It would be akin to driving a thumb tack with a 20 pound sledge hammer, and the end result could be comparable, hate to see that happen to any c4, especially the first year tpi. It should be preserved. Obviously if the op was talking about a built 383-400, or LS swap that would be different. But he has drivability issues, and is frustrated. He doesn't need a new efi system, he needs help to fix it. Just saying.

 

I think I had a different experience then most with aftermarket EFI. I got so tired of trying to tune factory EFI. I started with a 7747 ecu in my 84. Then I upgraded to a 411 PCM. That ran my first LS swap. But I HATE HP Tuners. So I tried Holley EFI. It came with transmission control and a wide band O2 that in already integrated into the harness. The learning curve with Holley anyway wasn't that bad. A big part of that is there are a ton of good videos and a good online community to help out.

Megasquirt is also a very good option. But I would avoid the Microsquirt unless you are using it for transmission control for a 4l60e or a 4l80e. If I'm not mistaken the Megasquirt has more inputs and outputs. I know the Microsquirt is batch fire for fuel and I don't think the Megasquirt is.

One issue that some people don't consider with any aftermarket EFI is will it pass inspection in your state with it. Here in PA they won't unless you have classic or antique plates.

 

Below is a thread dealing with est and EGR codes in a 1985 Corvette, has some flowchart info from the fsm, and has some links posted worth reading. I found that by Google searching "1985 Corvette est and EGR codes" it gave me 10 threads here, as well as a couple at third gen.org, and a couple at chevytalk.com forums. Sounds like your problem is in fact common for the 1985 c4

https://www.corvetteforum.com/forums...-1985-z51.html

 

I Def agree to get the engine mechanically sound before attempting any EFI conversion. No point doing computer work or tuning effort unless engine is totally mechanically checked out and cleaned up ready to go.

Post #9 mechanical checkup
https://www.corvetteforum.com/forums...post1605334191

I would follow that up with a fully engine cleaning, degreasing,
Post #39 engine wash
https://www.thirdgen.org/forums/tech...ml#post6470834

With clean engine and mechanically sound, most issues will have evaporated leaving just wires, computer, fuses, sensors.

Then, you get hands on with the OEM ecu and do whatever you can with that. Learn it the best you can. Read online manuals from Megasquirt, AEM, Accel, Haltech, etc... Read every book and use the knowledge to learn your limitations. Break it if you have to.
Also helps to brush up on mechanical advance and carb tuning.
And learn a little computer programming coding language.

Then you are ready for aftermarket EFI.

 

Thats correct on microsquirt vs megasquirt. Microsquirt is a very primitive system.

Depending on which megasquirt version you run you can have something equivalent to whats already in the car vs basically a modern EFI system. MS1 isn't much better than whats in the car already, MS3 has oodles and oodles of options. I went with MS2 on my 280z when I got sick of dealing with the ancient "computer" in it and it worked great.

Megasquirt can run batch fire or seq, for seq you just need some sort of way to measure the crank. There are MANY crank wheels for a 350 that mount on the balancer and then you can just rig up some sort of sensor. Once you've got that it also isn't very hard to go to a wasted spark or similar system and get more power.

 

It is called the idle air control valve (iac). It is located in the exact same spot of every 85-96 4th generation corvette on the bottom of the throttle body. If you had any fundamental efi knowledge about what gm has offered from 1985 to present youd be able to open the hood and find that idle air control valve in seconds. Even the later model cable driven throttle body ls stuff has basically the same valve located on the throttle body. This is exactly why I made the post I did, and the more you have responded, the more it becomes apparent that you need help. I am not trying to belittle or insult you, I am trying to help give you info pertinent to your described issues. I posted a link to a thread a few replies up with your exact stated issues.

NOBODY is trying to insult you, we are trying to help you avoid MORE costly mistakes. If you cannot find these components and use a scanner with factory service manual to see whats going on, and you just use an autozone code reader to replace parts when it says it has a code;YOU WILL NOT FIX ANYTHING RIGHT! Remove your feelings and ego from the situation, follow the link i posted a few replys up and start troubleshooting the car. It doesnt need additional timing when it is cold, it does not need fueling changes. It needs to have the wiring, mechanical, and vacuum lines of the egr and est system sorted out. it needs to have all codes cleared and actually fixed! Once you do that it will probably start, run, and drive just fine. If you cant find the info i am suggesting you have no business messing with an aftermarket efi install.

you need a General Motors FSM factory service manual for a 1985 corvette,NOT A CHILTONS OR HANES MANUAL! access to a tech 1 scanner, a digital volt ohm meter, a vacuum gauge, as well as hand held vacuum pump. you will also need a timing light as well as a way to test and verify fuel pressure. you should have a breakout harness for the tps sensor so it can be set right. and if you messed with the throttle stop screw odds are you have created some havoc and it isnt going to run right until everything is verified and returned to factory spec. The tech1 will give you codes, limited data. You take that info and reference the manaul where it gives you flow charts and follow it. you will have to check voltage on various circuits, you will have to verify all vacuum lines on the engine are in place without leaks and functioning right. if the intake has years of daily driver duty with 87-89 octane gas it probably needs removed, carbon scrubbed from the crossover ports in the intake, all egr passages cleaned. you will have to verify the engine mounts, cbeam, all engine accessories are in good shape and tight, the exhaust is right, the est module and knock sensor will pick up mechanical problems as knock and retard timing. I could go on and on. do you even know where the est aka knock module is? do you know where the egr solenoid valve is? have you verified base ignition timing is set to factory specs with the est wire disconnected? these are very basic things that every mechanic should have if working on a general motors obd1 vehicle. Do you have them? if not you are pissing in the wind, you will run around in circles, fix nothing, and probably remove good quality factory components replace with chinese junk and make the problem worse. Or, pay a master tech a couple hours labor to troubleshoot and fix the issues. the 1985 tpi engine is very tough, low powered but tough. it is not that difficult to get them to run right. If you cant sort these basic things out you have zero business messing with a microsquirt, its going to have you make connections to the cts, hei,mat,o2, as well as knock module. You just said you cannot find the idle control valve, and are unclear how the factory ecu uses that sensor to control cold idle. I am trying to help you dude. put your ego to the side and listen to what I am trying to communicate to you. Id love to see you out there burning up the streets with your 1985 corvette sir!