a big kick in the face

[joewoody]

working on a 2000 super air. after replacing my gt40 with a remand one I could not get the engine to idle correctly. my engine would idle fine when cold once I reached operating temp it would surge only when hot and shut down. I found similar post of problems kinda what I was having.i replaced idle air controle valve twice one counter part and one pcm. a new throttle positioning senser. new distributor - cap rotor wires - coil. fuel pressure regulator. no fix still . then I replaced low pressure pump due to low fuel pressure I thought was low. was holding around 30 ish. still no fix . I then replaced high pressure and map sensor thick film ignition module and threw all of this yes I checked the relays first. checked tank cleaned tank . I replaced all fuel lines. tore the motor apart replaced all gaskets checked everything for air leaks no leaks. talked with pcm several times threw all of this. I am working on week three. countless hours and I felt I was all in after this I am going to figure this out. today i get a phone call from mike or mark cant really remember but anyway he was with pcm. he says do you know how much over the cylenders were bored on the remand engine. I said no he then tells me the pcm ecm will only calculate for up to 20,000s over for bored cylenders. they had some isues in the past about the sytems not operating correctly if they are over 20,000s. point blank system will ask for more air and the iac will max out and shut down. so after talking with him for about an hour on if their is a fix the only fix is to change the motor. really again their is no way. well I called the company that I bought my motor from and asked what it was bored over and he told me 30,000s I then went into talking with him about the pcm system and I don't know what the outcome of this is going to be but im probably going to have to pull this engine again and get one that is only bored up to 20,000s over and my engine guy take this one back.

[MLA]

Not buying, sorry. What was the reason for the engine replacement in the first place? What was it regarding the cylinder volume that the ecm could not calculate? IIRC, thats a speed/density system. I have never seen a reman bored engine have such a swing in engine vacuum, that the ecm could not compensate. Id be willing to bet that that bored engine has better vacuum then your old engine.

Have you confirmed cam timing? Compression and lead-down test? vacuum leak? how fresh is the fuel? Fuel pressure/volume? Is there one or more cylinders missing at idle?

[mosh706]

I agree with mla on that one. I would also check the ignition module located on the distributor. That fuel injection system is the exact same one used in the 87 mustang 5.0 they are extremely easy to use and can handle heavy engine modifications.

[core-rider]

I have heard this same thing before about over-boring the engine and the PCM programming not working well with it. I don't comprehend how it wouldn't give the very simple programming the EEC-IV computers had. They aren't that "smart" and never have I seen an issue with it in cars. I really don't see why competent tuner for cars couldn't crack into the PCM computers and tweak for things like this IF it really is a program issue. 0.030" I snitching in the grand scheme and should keep an engine from running correctly.


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[CradGen2]

I'm not a mootr guy, but this thread in very interesting. I understand the below, but can't imagine 10K causing this. That said, PCM knows their stuff, so if they say there is a programming issue I would believe it.

[joewoody]

com test 160 + on all cylenders, complete new distributor from skidm. leak down test over night after new pumps holding 38psi running at idle 41 wide open 38. 3 day old fuel. if I run it for more than 30 min it will foul plugs. pull them out they are white way to lean. but the ecm controls that. if anyone has any other ideas I woulkd love to hear them I have a list of parts and no fix so I just want it to run right. timming set to 5 btdc at 2000rpm with spout out has not moved ive tried moving 5 each way no change

[ffmedic74]

If cylinders are bored out more, why not get higher domed Pistons to compensate so you then remain at the same CCs that are recommended by PCM?

[TRBenj]

If cylinders are bored out more, why not get higher domed Pistons to compensate so you then remain at the same CCs that are recommended by PCM?

So to compensate for the larger engine displacement due to the overbore, you suggest raising the compression ratio? Those without a clue as to how an internal combustion engine works might want to read with their eyes instead of typing with their fingers.

Just a nitpick- we're talking 20-30 thousandths, as in .020-030", not 20,000-30,000".

GT40's do in fact use a fairly simple MPEFI system that shares several components with late 80's and 90's vintage Ford vehicles. The biggest difference between the 2 systems is that the GT40 runs closed loop- meaning it cant adjust the intake parameters (air and fuel) based on output parameters- it has no way to measure the latter, as it does not have any o2 sensors in the exhaust system. The current lineup of PCM MPEFI engines can do this, but the GT40 cannot. Instead, it runs based on a predetermined set of air and fuel tables based on atmospheric conditions. It cannot change the tune based on different engine internals (displacement, flow, compression ratio, etc) as it has no way to measure them.

That said, I am surprised that such a relatively small change in displacement would cause issues with the ECU... but if Mark from PCM says its a known problem, then I'd believe him. Especially if youve ruled out a lot of other potential causes at this point.

[ffmedic74]

TRBenj... Thanks for the shot to the chest! I suggest an idea slightly higher domed Pistons to compensate for the over bore so you end up with the same total cylinder volume as he originally did. Again, an idea to see if he can save some money. The forum is a method to help one another and idea generation, correct? Sounds like even PCM was stumped for awhile. Joewoody... Hopefully you find a solution soon.

[core-rider]

Is there a possibility PCM could re-map the ECM to compensate for the added CI? I mean we are talking about 4-5CI here. It's not like he went from a 351 to 408 stroker or something. Eventually more engines will need rebuilds, replacement, etc. and over-boring an engine .020-.030" is pretty standard practice. Are you telling me PCM never thought about this and in the future all PCM GT-40 engines will be anchors because the ECM can't adapt or be adapted for a simple over-bore???

I still see it in the realm a possibilities that a good tuner could make this work. It may take some trial and error, but some time spent on the water with a laptop tweaking air/fuel maps should be able to yield good results.

The guys at N3 Boatworks are into hot rodding cars, boats, etc. They seem like a good candidates to take on a project like this if PCM can't step up. I'll do a little checking around with my old rodding friends and see if I can't find a good tuner in your area that might be up for the challenge.

[ddipert]

In lue of remapping the ECM a cheap way to do this would be change the fuel pressure. The ECM map should should not need to be changed since we are talking the same cam/exhaust/etc but this higher fuel pressure would cause the EMC map to think it's putting out X but it would really be putting out X+(increased % from raising the fuel pressure). This is a way to adjusted some cars/motorcyles if there wasn't anyone tuning ECM.

I do find it hard to believe that this little of a displacement change could cause this. At idle there is very little demand on the fuel system you could be way off at idle and it still should run. Another idea, what themostat is in it? Could you change it to a lower temp which would adjust the fuel map since it would always be "cold"?

Engine displacement and domed pistons.
If you have a cylinder the only way you change change the volume is by making the cylinder longer (stroking the crank) or changing the diameter of the cylinder (boring). If you dome the piston then your not changing the displacement of the engine, you are increasing the compression which in this case would be worse.

[ffmedic74]

[ffmedic74]

Great example of too much stroke and compression. Personal testimony last fall 383 stroker crank and srs 14:1 Pistons. The fuel system is complex but fully adjustable.

[ffmedic74]

[joewoody]

ill try thermostat I have a 160 in it ill go to a 140 and see what it dose and if it helps. as far as the tuner goes im not wanting to spend a grand on the system that will work or two thousand on the piggy back ecm that is made. also was wondering on an adjustable fuel pressure regulater to bump up fuel pressure even more to compensate for lean condition. loving ideas keep them coming I will figure this out