Fuel Issue, sputtering, dying while running

slpell · September 1, 2016

Hello, I am new to this forum, I've owned several SC400's over the past 15 years. I currently am driving a 1994 V-8 Coupe. In regards to fuel starving issues I'm reading, I have the following info. My 94 SC400 recently is stalling out as though it's loss of fuel, with no regularity. Always restarts, sometimes runs for seconds to 1/2 hour, but always dies out eventually. It has sputtered out from just 2 minutes of running to an hour or more. I recently have been using premium gas only and since, this condition has occurred. Considering a tank full of BAD gas, I've been recommended adding dry gas, to displace water moisture, changing the fuel filter and draining and replacing fuel. I've done all of the above with no change in symptoms. After investigating further, this and other forums recommend fuel pump control unit, fuel ecu- are these two in the same please ? Also, TPS-throttle position sensor. I'm trying process of elimination, will replace the TPS tomorrow and hope for success, Any suggestions will be appreciated, thanks to all, a very welcome forum. Larry

TrevC · September 5, 2016

Hi Larry....welcome to the Forum!

I think I would agree with you on the fuel pump control, although I would look at the system relay first as its the cheapest and also the more likely candidate for failure.

Also, have known numerous cars with similar symptoms have problems with TPS.

The only real way to diagnose it to run a scanner in the OBD whilst on a drive and record the parameters to see what goes offline first...e.g. fuel pressure, tps signal. This generally narrows down the fault without having to replace too many parts to start with.

Let us know how you get on with it.

Cheers, Trevor

slpell · September 5, 2016

Thanks Trevor, actually I have a small used car lot and have a wrecked 95 SC 400, to avoid my local diagnose shop that's pricey, I have swapped the TPS, Fuel pump Control ECU, the fuel pressure regulator, installed a new filter and fuel pump. Nothing has worked. The diagnose equipment is crucial, won't go though this again. It's going to shop tomorrow. Thanks for your reply. This one's being chalked up to experience, Larry

slpell · September 5, 2016

Hi Trevor, thanks again for your reply, I even swapped all relays in fuse box with no improvement. Have you ever heard of a main computer or fuel injection ECU being an issue in this vehicle? I have a good mechanic buddy bringing his Snap On scanner tomorrow. This has become a real stickler. Thanks Trevor.

TrevC · September 6, 2016

ECUs don't normally fail as a rule but see what the scanner reads out and let us know the outcome please

slpell · September 6, 2016

Well, first of all, I need to thank you Trevor, as well as anyone else who had participated for your consideration in my dilemma. I certainly appreciate it. I did, this morning retrieve a used ECU, main engine control unit and installed it in my 94 SC 400. As a youtube video mentioned, the check engine, overdrive and trac lights starting flashing. This is supposed to be the new unit learning new components. The engine started immediately and is still hours later doing well. Lights are still flashing, not sure how long that will take place, but cheers to Trevor and the Lexus Forum, I'm on the road again,,, you're the best---- Larry