Andyls

What could cause my 94 ls400 to cut out when I press the gas past a certain point? It would stumble a little before the pedal hit that point before I changed the tps.Tried new fuel pump and filter. Jumped the fuel pump at the diagnostic terminal and tried driving it with the jumper in, no help. I got a code 41 (tps sensor), replaced that best I could, by that I mean the only one I could immediately obtain was off a 94 SC400. Different part no but it seems to work. Turns out I did have a faulty tps but that is not the cause of my main problem. In park or neutral I can floor it with no problems but under a load it feels like its cutting the fuel or spark off and on, just like I was turning the key off and on. When I let off the gas it returns to normal. Since I replaced the tips, it runs perfect unless I push the pedal too far. Any ideas? I'm stumped. By the way, this is my first post so if I'm in the wrong place, let me know.

LScowboyLS

did you use a TPS from the dealership? - the only TPS's you want are marked either Toyota, Denso, or Aisin.

Did you use the service manual to troubleshoot the TPS? - Were there any other other simultaneous codes? - Did you use the correct procedure from the service manual to adjust it once installed? - check that as well.

If all of this seems fine, then remember that a code 41 can also be caused by an ECU issue, and 94 models have a very common problem of failing ECU capacitors, which can cause the kind of symptoms you have. Yamae's ripple test can verify bad ECU caps.

Andyls

My tps is from a salvage yard but it is a Toyota part. I used a different method to adjust the TPS. It may be a little out of adjustment. I haven't checked the caps in the ECU (yet). Thank you for the reply and the links.

LScowboyLS

read the information in all four of those links I posted, that should clarify a lot!

RamAirRckt

Unplug the MAF, it will set a fail code (I am assuming there is no codes set now?), then see if the problem goes away.

When on the MAF, the ECU uses the MAF for airflow calculation data, when the MAF fails, it has to fall back on VE tables (Volumetric Efficiency) to make the Speed Density calculations. If it runs good on SD, then look at the MAF..

TPS will rarely if ever be a problem for fueling, it isn't used for that, MAF and coolant temp, intake air temp and O2's are used for fueling. TPS is used for canister purge and transmission shifting primarily.

LScowboyLS

so far, so good

will all due respect, this is completely incorrect.

The throttle position sensor (TPS) is mounted in the throttle body and detects the throttle valve opening angle.

The TPS is critical for the operation of the fuel injection system on the LS400 (and every other fuel injected car I have ever seen in the last 30 years) - when the ECU cannot determine the throttle position, the entire process breaks down and the the car will run terribly, if at all! - yes, the TPS and a separate throttle cable are also used for the transmission, but the TPS is nearly as critical as the crankshaft position sensor or the cam position sensors in the calculations the ECU uses to run the car.

It is critical to increase the fuel rate as soon as the throttle valve opens; otherwise, when the gas pedal is first pressed, there will be a hesitation as some air reaches the cylinders without enough fuel in it. The TPS monitors the throttle valve position as this information is key to the ECU making correct decisions about the right fuel and air amounts in response to the driver's pedal input. This is analogous to the accelerator pump function on a carburetor equipped car.

Andyls

Thanks for the great info, and sorry about the crazy hours I keep. I work evening shift. I actually already have the MAF unplugged due to a mechanic friend trying to be helpful and cleaning it for me I have to replace that but it runs great and I actually have a little more pedal with it unplugged but other than that nothing has changed. I'm a little worried about the TPS I'm using since it is not the correct part #. It fits a 94 sc400 but it seems to work and it was handy. Completely cleared up the sputtering problem.

Andyls

I'm convinced the ECU would be the next thing look into. My AC compressor won't kick on and my instrument cluster is acting up so if the caps in the cluster are going bad, the caps in the ECU probably are too.

shanjam

could be dirty air filter or crank sensor

LScowboyLS

a dirty air filter will not cause a car to cut out under load!

in fact, here is some trivia, did you know know a dirty air filter actually filters air even more effectively than a clean one? - the trapped particulate actually functions as additional filter media to help trap future particulate!

Andyls

My air filter is clean, just checked it right before my buddy ruined my MAF. I need to get the capacitor to do Yamae's ripple test.

LScowboyLS

send me your address and I will mail you a capacitor

or you can also just pull the ECU and take photos

Andyls

I sent you a PM LScowboyLS. Thanks again.

Andyls

I don't really trust rebuilt ECUs from eBay etc. and I'm not confident in my ability to do it myself. Any recommendations in Southeast Missouri if I get the caps?

Sc0pe

iTrader: (1)

I think you can post in one of the regional boards (not really sure where Missouri falls on the map, in terms of region, so pick the right one for you) and ask around to see if anyone would be willing to take you up on that ECU repair. Alternatively, I'm sure there are members on here that are more than capable and would probably do it if you mailed it to them, just ask around. Heck, check around town for any advanced computer technicians who might be up to the task.