poor acceleration

[boppo]

Hi i hope someone can help, i have a 92 LS400 that has poor acceleration after warm up ,the problem varies but is always there.this is what i've done so far
TPS replaced / MAS swapped / injectors serviced / filters replaced / faulty 02 sensor replaced / cam timing checked / cats checked / fuel pump ecu bypassed
both the local Lexus dealer & a EFI specialist failed to diagnose the fault even though we were able to reproduce the fault on the dyno with 80rwhp one minute & 160 the next
has anyone got any ideas what too check next? or better still has anyone experienced a similar problem

PLEASE HELP

 

[Zuffen]

Whilst it's easy for me to say as I'm not the guy fixing the car I'd start by looking for a wiring fault.

My reasoning is the fault drops in and out so it's intermittent. Wiring is the most likely culprit.

Check all you earth points that they are clean and tight. Particularly under the battery.

Once you've done that (if not successfull) start looking for faulty clips at loom ends and then for daggy/frayed/broken wiring.

It's a long tedious process but be methodical and keep notes.

When you solve it post up the answer as the more information we have the better for the future members who suffer similar problems.

 

[boppo]

I'll give that a go
I'm willing to try anything at this stage

 

[Peewee]

When it drops down to 80rwhp does it sound like a diesel? Like its only firing on 4cyls?

I had this problem with mine (albeit running on aftermarket ecu and bosch ignitors).

The car would just almost suddenly stop.
So I started looking at things, suspected a few things, changed a coil for a spare one and it was fine... for 3 days. Then it was back.

Then I changed the ignitors for some new ones, and it was fine.... for 3 days.

Then I pulled apart all the coil/ignitor wiring, redid it all, put the original coil and ignitors back on and it was perfect again... for 3 days.

Then I reswapped on my new ignitors and its been perfect since.

It was just a combination of faulty ignitor and poor wiring... albeit my wiring.


May not be of relevance to you, but its something to think about.

Check connections, check earths, they can corrode.

Next time its running poorly unplug one ignitor, see if it makes a difference. Then plug that back in and try the other one.

 

[boppo]

it still runs smooth when it looses power, it's like someone has jammed a rag up the intake or a spud up the muffler-- when you lift off the throttle (even to half throttle)you feel a slight improvement ,i had theorys on knock sensors and timing retard but its probably fuel related, in any case like you said its probably a wiring issue its just unusual that you'd get that with a stocker
I'll start searching tomorrow night ,wish me luck

 

[Peewee]

Did you have an AFR sniffer up the tailpipe when it was on the dyno?

Go to someone with one of those OBD computer thingy's.
Test the timing and knock when the bad thing happens.

 

[Zuffen]

People often ask me "what's the weak link in a 1UZ?" my stock answer is the wiring loom.

Think about it the loom lives in a hot, corrosive environment for 10-15 years. how would you feel if you were forced to live there.

Looms look like the limiting factor on longevity of 1UZ's.