26 HP EFI Command Pro: Absolutely at wits end

I started a thread about two months ago over here.

Cliff notes:
Husqvarna ZTH 7226 I've since tried everything I can think of and still have the same problem. Engine starts up fine, and usally when it gets close to temp, it starts hunting and then stalls and dies. On two occasions, it's run like a champ with no issues, once running for nearly 4 hours mowing, towing, and doing laps around my buddy's trailer park.


Picked up the mower in February for what I thought was a good price. It had the same issue of starting to slowly hunt when heating up and getting progresivley worse to the point where the rpm would drop to where it would stall. The issue seemed to be fuel related to me (throttle changes would make it bog like a carb with too big an accelerator shot), and looking at the fuel system patch work, I thought it would be an easy fix. Cleaned the tanks, installed new lines and filters. Fired right up but quickly found the issue persisted. I checked all my connections, installed new fittings where i thought they may be even questionable and installed a known good fuel pump. Ran good for about 45min with varying throttle, rpm, load and pto on/off. I deemed it good and went back to make everything nice and neat....Went back out the next day to finish mowing and the same f#$@ing thing!!!

Checked the computer, and found TPS code. WIthout doing ay further troubleshooting ordered a TPS and installed....Same issue. Tested TPS resistance through its range at sensor and at ECU. Went through the TPS learning procedure, but could never get the MIL to confirm things recalibrated...I gave up and brought it to my old ladys friends husbands place (he works at a mower shop). We chased down each ECU wire to its end and checked for connectivity. Fixed a questionable ground and it ran for 4 hours....Everything seemed great, the sun was shinning, life was good I FINALLY had a good mower...Untill we went to put it on the trailer...same thing!!! Pulled the oil temp sensor thinking that keeping it from going open loop would make it run...nope

He did some more testing of rail pressure, sensors, etc....As a last ditch effort he sonic cleaned the injectors and rail....to no avail.

I dont have the money to take it to a shop and have a scanner bolted on this thing. I've been scouring craigslist for an engine that will pull this thing to no avail. Neither of us can figure it out...has good compression, spark and is getting fuel (although i cant verify injector duty cycle when at temp). Please...help

James

Although this is a fuel injected engine, there is another thread on here in which a carbureted engine displayed the same symptoms.

The problem was determined to be heat related; a heat shield was either touching the exhaust system or otherwise mis-located such that the gas in the carburetor was boiling.

Even though you have no carburetor, maybe something similar is happening to yours. Here's a time when it would be mighty handy to have an infrared thermometer.

I've got an Infrared non contact thermometer, I'll give it a shot tomorrow. Although, it's a return style system, so I wouldn't think it would be hydroloc or anything of the sort. Especially since it's happened on cool.ornjot days and worked on average days


So I know where to look, Where was the heat shield interfering?

My last resort tool is a colortune By Gunsons.
Basically t is a spark plug with a glass section so you can see into the cylinder while the engine is running.
Thus you can see if it is running rich / lean or no fuel at all .
It is set up to rim rim fire so you can also see the quality of the spark.

Now I have never used one in a computer controlled engine so don't know if it will work or the ECU will throw up a spark plug problem and shut down but at $ 70 worth it's weight in headache pills.
On a low speed mower engine it should be fine just remember the window is only a lump of pyrex so don't rev the engine hard while looking directly down the plug ( it has a long tube & mirror )

I can't find the other thread. I did a search on my user name but I must not have commented in it.

In general, heat shields are used to protect other areas of an engine from the exhaust system. I can't tell you where to look or what to look for on your engine because I'm not familiar with it, but if any exhaust piping runs close to the EFI system, it probably should have a heat shield protecting the EFI system.

bertsmobile1: when I pulled the plugs they were carbon fouled from running rich. I assumed it was due to staying in closed loop mode, and never getting to run at temp and clear out.

The muffler is close to the heads/injectors/tps. But The temps seem to be what I would call exceptable range (nothing above 100).

I'm guessing its and efi specific issue, but I can't tap into the ecm to see what the parameters are