MegaSquirt Help!

TonyK

TonyK

True Classic
With all the bits bolted to my car I finally tried a start. It coughed I pumped the pedal a bit, just like the carb fed engine and it started. With the guages lit up in Megatune the engine ran rough, really rough died, didn't catch on fire and I only had 4 fuel leaks. And 1 coolant leak. With port injection comes a new problem that the carb does not have, is one runner not getting any fuel and the smell from the burn is very rich. The Air Fuel Ratio is pegged at 28 and I have no idea where to start. So the simple things first, fix the fuel leaks and the water leak which required removing the manifold after I dropped the coolant.

According to the Mega manual if you have to press on the gas pedal while cranking then the mixture is rich.
No Kidding.

This summer I insulated my shop, installed a new dry wall ceiling and painted it and installed siding over the concrete block walls in an effort cut down on the drafts in the shop and work on my car with my new hoist. Problem is that the exhaust fumes are killing brain cells and if this post doesn't make any sense, then pray for me for a quick recovery. I purchased a rubber exhaust flex hose and vent I will install this weekend and try this whole thing again.

Back to the engine.

My 1500 engine is running about 9.5 compression with a 40-80 Fiat camshaft. 25 years ago my wife's parents went to Italy for 8 weeks and I asked them to find me a 128 camshaft from the wreckers. They talked to a cousin and he went about finding me this camshaft, tagged 40-80 with Fiat cast into the shaft. The idle with the carb was loppy at 1000 rpm and it ran rich at idle. Cold starts were always a couple of tries as it would hit, then require several pumps of the pedal and try again. Warm up idle was about 1400 rpm. After that 1000 was obtainable.

So I increased the throttle body stop to allow for a higher idle. Still running rough. Not knowing what cylnder was missing I took a wet rag and touched each exhaust manifold runner to find out if one was cold. #1 seemed the coldest as it would not sizzle the wet rag. Now where to start. The car ran fine before I removed the carb, so I opted to change an injector on number 1, no difference, I pulled and flamed the plug with a torch and when I went back to install it I realized that the dizzy cap was shifted. Removing it, it was apparent by the gouge in it that the cap was hitting the rotor and missing #1. So I set this straigh and started the now warm engine. The RPM was a bit rough as the AFR climbed making fumes. I changed the engine constant telling the computer I had 190cc injectors instead of 168cc. Started again and the AFR was at 14.7, steady with a 1600 rpm idle, as I adjusted the stop on the throttle plate to decrease the idle the AFR started climbing and at 1000 RPM is running rich. Like really rich. Any ideas here? With a carb the idle jet is fixed and by opening the butterfly a bit sets the AFR. if the engine went lean it would die. With MegaSquirt as the idle decays a bit, the computer starts feeding more fuel to compensate. How do I peg the computer to maintain the AFR and not gas myself.

Thoughs? The fuel pump sprang a leak, so I have it on the bench and am rebuilding it. Will be a few days before I can get back to this project.

Thanks.

TonyK Grimsby Ontario, Canada.
 
Hi Tony,

You need to thoroughly read the MegaManual. Then read it again. And again!

The computer is doing whatever you have told it to do, by way of the engine constants and the Volumetric Efficiency table. Have you set all the engine constants as per the Manual? Have you loaded a reasonable VE table? Can you post us a screen shot of the VE table you have?

It sounds like your VE is too high around idle rpm, hence the running richer as you closed the throttle.

You shouldn't change the injector size to fool the computer. Temporary adjustments can be made to the req_fuel number to get the engine running. Once you have it idling ok, switch off and scale your VE table x "false" req_fuel / "correct" req_fuel so that you can use the correct req_fuel value again. For example, if you had to halve your req_fuel to get it idling ok, for the next run scale your whole VE table by 1/2 and re-enter the "correct" req_fuel value.

Once you can get it idling ok, you can start tuning the rest of the VE table. If you are running MSII, disable any afr correction and use the self tuning feature to gradually get your VE table in better shape.

The above is a very brief outline - it's all in the Manual!

Congratulations on your excellent FI conversion, and on the engine start without burning your workshop down; best of luck with the MS tuning!

All the best, Rachael

PS My Alfa 3.2 V6 conversion is now in progress with Nick Troth at P1X-2000. I hope to get some progress pics posted in the ensuing weeks.
 
Tps

I have TPS from a Honda D15b engine with throttle body. It appears to be calibrated correctly as I press on the pedal a corisponding gauge in Megatune shows the TPS posistion.

TonyK Grimsby Ontario, Canada.
 
Required fuel.

I have read that dang manual to the point that I don't know what I am reading any more.

I am running MS1 Extra for fuel only. In the constants page the only way I can see to change the required fuel is to over state the injector size to get it to fire a shorter pulse.

I have looked at the VE table and enrichments. However being that I am so new to this, I struggle with it. I understand what you are saying by changing the constant, as for a while when I obtained the good idle at 1400 rpm, opening the throttle body caused the mixture to go lean and die. The manual states not to mess too much with the VE table as I will be tuning to each specific point on it. But, you bring up a good point that possibly just altering the table at idle may be nessessary with my engine and after that all might be a closer tune on the table to my engine.

The throttle body has the cold start by pass passage in it, which I currently have the ports taped off for no flow. The cold start by pass has a water heated jacket that currently I am having water flow problems with. Maybe if I get that working, the added air will lean the mixture and I can close the butterfly setting for idle a bit as well.

As trouble shooting goes, I know this is more than 1 problem I am looking at that collectively place me where I am.

Thanks for the response and help, all possiblities will be considered and implemented.

TonyK Grimsby Ontario, Canada.
 
Tony,

I know what you mean about the Manual, it is a monster. MegaManual is well named!

The VE table is the means by which you tune. Yes, you don't want huge variations between adjacent "bins", but don't be afraid to move the points up and down, and to see a fair degree of change over the whole table. For example, my Uno Turbo engine has a VE table that varies from 35% around idle up to 120% at full throttle.

When you are entering the engine constants, you calculate req_fuel with the little utility program, after inputting your engine displacement, number of cyls, injector size etc. First off, use this calculated req_fuel, and make a note of it somewhere handy. Then, to get your engine idling with the given VE table, manually alter the req_fuel value up or down (usually down in my experience!), sending it to the controller each time, until you get a stable idle.

To get a smooth idle what you should have is rpm bins around 700, 850 and 1000 rpm. Then you need to have a little hollow in the VE values, say 45, 40 and 45 at 700, 850 and 1000 respectively. Then the 850 rpm bin gives you a good idle; if the engine stumbles and dips towards the 700 rpm bin it goes a bit rich to help the engine recover.

Once you have got it idling well, switch off and scale the whole VE table so that you can re-enter the original req_fuel value that the utility program gave you. Now you have the correct req_fuel and correct VE at idle. From there you tune the table by giving it a few more revs to get to the next rpm bin and seeing what happens. If it is too lean, raise the VE points around the bin, if too rich lower them. Carry on until you get the engine running well up to say 3000 rpm. This gives you a reasonable VE table for the off load areas, i.e. high manifold vacuum, along the bottom of the VE table.

Now you can try moving the car under power to get to the higher manifold pressure rows. You will probably find the VE values have to climb fairly fast to keep the engine running under load; the symptom is the engine dying as soon as you try and release the clutch to pull away. Be patient, keep raising the VE values until you can nurse the car into moving.

Once you can keep it running with the gentlest of pull-aways, you can start to give it more throttle and get tweaking further up the VE table.

Regarding your cold start bypass passage, allowing extra air through the bypass will have absolutely no effect on your a/f ratio. MS has no air flow meter; it only sees the pressure in the manifold, it doesn't know or care how the air got in there!

Cheers R
 
Last edited:
Thanks for the Info.

With the cam shaft I have it is difficult to ever get a 850 idle, so I may move the bins up a bit. Say, 850 as the bottom and then 1000, 1150 and 1300.

I did try what you suggested before this post by altering the VE table, from the tools specific menu to a lower value and the AFR came to 14.7 and the idle balanced out at 1600, rpm actually came up when the mixture leaned. Then I got reading and the text got me on another track not to mess with the table too much. So you have gotten me straight on this and I will dabble, once I get the fuel pump leak resolved, ( used pump) may have to buy a new one. The by pass with the water jacket is a nice touch as it allow more air for warm up much like the Bosch unit, ( not electric).

It is a challenge, thanks again for your comments and help.

TonyK Grimsby Ontario Canada.
 
You must log in or register to reply here.
Back
Top