93' LS400 "Limp Mode" Fix + Fuel Issues

Turbros Garage · April 11, 2016

What's up guys this is my first forum post so bare with me and i have a couple of things i need answered and things I've fixed. Well i purchased a 93 LS400 and didn't test drive it before buying (probably should have lol) but it ran very bad and shook the whole car. You could smell unburnt fuel from the exhaust and was gonna see if it had a code but the dash lights dont work. I've purchased the specific capacitors and know how to fix it (basic soldering skillz). I jumped the gun and thought is was a spark issue so we removed the plugs, plug wires and tested the resistance on each plug wire and they were all in spec (less than 25k Ohms). Next checked the plugs and 1 and 7 have ignition firing residue while 3 and 5 were soaked in fuel. On the opposite side 4 and 6 had firing residue and 2 and 8 were soaked also so i found out that 2,3,5,8 (the ones soaked) where connected to the front most engine coil. Tested the coil and saw no power coming from it to the left side distributor and realized the coil might be bad. Replaced the coil and she purrrrrs like a kitten. The non firing cylinders had some oil in them for some unknown reason and smoked a little but went away. So I had it idling and gave it some gas and had a little bog in higher rpms. Then not thinking anything of it, I took for a quick spin around the block and ran well until i floored it and the car just died. Coasted to a stop tried starting her up but just cranked over for a second then died. Crank up for a second then dies again. Next thing i thought was the fuel filter since I know they usually cause LS400s to die on hard acceleration. Changed the filter to a new one, put my mouth to the old one and was pretty clogged. The new one flows so much better. But here's the problem, I replaced it, turned the key and same problem. Starts for 1-3 seconds then just dies, no matter what i do with the pedal. Checked ignition and its fine so definitely a fueling problem. Also I can't hear the pump prime anymore which warrants concern. I've heard of fuel pump relays going bad, or worse the fuel pump ecu or even worse THE ECU! We tested the fuel pump and on cranking it shoots fuel out like crazy from the filter. What do you guys think? Just fixed one problem to encounter another so I hope this isn't a vicious cycle. Also got a fresh $100 to whoever can help me fix this!

chc0318 · April 11, 2016

What's the Diagnostic Trouble Codes? If you don't know, please try follow

http://www.lexls.com/tutorials/intro/codereading.html

to get it.

Turbros Garage · April 11, 2016

14 minutes ago, chc0318 said:

What's the Diagnostic Trouble Codes? If you don't know, please try follow

http://www.lexls.com/tutorials/intro/codereading.html

to get it.

That's the problem, since my dashboard lights flicker and then die, I can't tell if the CEL is on or not. I'm fixing the problem currently but just want to see if anyone else has a good notion of what's wrong

chc0318 · April 11, 2016

capacitors leaks is the common problem, Both dashboard and ECU have been fixed by send to ebay store. the sozzt is around $100.00 each.

I guess your ECU cause the problem.

Turbros Garage · April 11, 2016

1 hour ago, chc0318 said:

capacitors leaks is the common problem, Both dashboard and ECU have been fixed by send to ebay store. the sozzt is around $100.00 each.

I guess your ECU cause the problem.

I tested the ECU to see if it was powering the fuel pump and it was fine. B+ is power from the ECU in the diagnostic port and I get +12V. I jumped the pump and it stays on but while cranking it still starts then dies. Relays all check to be good too

chc0318 · April 11, 2016

As my experience, malfunction ECU cause all kinds of problems, you need to make sure your ECU is fully functional.

Turbros Garage · April 11, 2016

Update: Replaced the fuel pump with a direct replacement and still the start up and instantly die issue. Next we bridged the diagnostic port to keep the pump on all the time and you can hear the pump working. Still starts up then dies. we removed the bridge then tried to start and it ran and idled smooth. Then i gave it a full throttle romp on it and it went to about 3k then just died. Starts then dies. We know the engine is getting good ignition since it runs on starter fluid like a charm. So ruling out the ignition, pump, filter, pump ecu it seems to be an injector problem or grounding issue but as erratic as it is it could be the harness in the trunk so i'll check that. If that is OK it may be the ECU.

Update: Checked the injectors and they are getting constant power and are firing off when supposed to. ECU is good. Since it dies at idle could it be the IACV? (Idle air control valve)

billydpowell · April 12, 2016

do yourself a favor and go to http://www.lexls.com/ and do a little reading, look for "trunk hinge wiring harness" problems..

Exhaustgases · April 14, 2016

If it starts and dies its not seeing an rpm signal. You may have either cam or crank sensor or ecu problem. With no signal ecu opens the circuit opening relay.