rwdaddict

So I bought a beautiful 94 LS400 with 194k on it. First thing I did when I got it was change all the fluids, air intake, plugs and wires, caps and rotors, trans filter, trans mount, clean the throttle body, made sure the throttle cables were within spec, fuel filter, a can of Seafoam, also a can of techron through the fuel tank, checked the wires in the trunk for breaks, tried two different AFM's, did at least 4 drain and fills with the trans.

Now onto the persistent issues I keep having. Seems after the car warms up it will kick and surge with 40%-80% throttle and even sometimes at WOT. Shifts are strong and pulls pretty good when i'm rolling and punch it. When I punch it off the line it feels like the clutch is slipping. Which could be a bad torque converter and i'm hoping will go away when I figure out this kicking and bucking.

I've done a few weeks of research and the list in the first paragraph is from suggestions on this forum. I'm tired of throwing parts at it as the few things that are left like IAC or TPS are no cheap fixes. I'm going to be putting in a new temp sensor to see if that helps but I'm getting frustrated.

Things I still need to test that I've seen semi-related to my issue
- Doing an EGR delete this weekend
- Putting on a new temp sensor
- Going to cut the exhaust manifold cats with straight pipe. (in my county only 95' and newer have emissions)
- Still need to multi-meter test the TPS
- I heard about jumping the fuel ECU but can't find a good how to on which leads to jump.


The problem with most of these "fixes" is that the user usually has some check engine light and rather than fix the damn light they'll crawl to the forums rather than fix what the car has already diagnosed for them. I wish I could be that lucky, but no, i get a ghost issue

Any help would be greatly appreciated.

rwdaddict

Almost forgot, I also swapped the ECU with a rebuilt one.

LScowboyLS

NOT a good plan - I would rethink this, stock EGR is reliable and very unlikely to be the issue


very good idea


NOT a good plan - I would rethink this, the stock catalytic converters are very reliable, do not cost any power, and very unlikely to be the issue


testing and calibrating TPS is fine, but these tend to be reliable


this is a possibility, search for Yamae's posts on this, he explains exactly what and where to jump


I have looked at over 100 "rebuilt" ECU's for LS400, from dozens of different sources (ebay, driftmotion, craigslist, online ECU rebuilders, etc.) and have yet to ever see one rebuild using the correct type of capacitors which must be premium Japanese high temperature, low ESR, high ripple rejection, long life type, these are a very rare type and rebuilders are apparently ignorant of the right caps to use or just being cheap, or do not realize the importance, or don't know where to buy them, not sure what the problem is, but on a 94 model, failing ECU capacitors is by far the most common cause of the symptoms you describe, though not the only possible cause. (sometimes it could be something as simple as a bad coil, or fuel delivery issue, do you have a fuel pressure gauge? - I like to tape the gauge to the windshield where I can see the reading while driving, and then monitor the fuel pressure when the "bucking" starts)

another common cause is a bad AFM, from being improperly cleaned (someone used solvents) and I know you have tried several, but they ALL may have been "cleaned"

rwdaddict

This is the buyer i got the rebuilt one from
http://www.ebay.com/itm/93-94-Lexus-LS400-V8-Engine-Computer-ECU-ECM-1UZFE-89661-50140-REBUILT-/111206045607?pt=Motors_Car_Truck_Parts_Accessories&hash=item19e46597a7&vxp=mtr
I screwed my first sensor by cleaning it while i was doing my initial tune-up. Just something I always do when i get a new car to me. If I only knew, haha. The AFM i got from AutoZone which looking at it was obviously a junk yard part but i'm sure it multi-metered out well.

I'm going to put that Temp sensor in tonight, along with testing out my TPS with an OHM meter. Then i'm going to jump that fuel pump. Don't have a Fuel gauge to test with

LScowboyLS

as far as the ECU, if you have a high end multimeter, you can use Yamae's ECU test, I have the correct test capacitor if you need one - otherwise, I would advise pulling the ECU, take some high resolution photos such that Yamae and I can see the actual numbers on the capacitors and their polarities, and we can then tell you whether the correct capacitors were used.

DaveGS4

iTrader: (2)

First question... was the car surging and bucking BEFORE you did all these things or only after?

rwdaddict

Before and after, it seems to only do these things when the car is warm now when before it did it all the time. Not sure what that's telling me.

cobalt91

Does the check engine light come on when you turn the key to the on position with out starting the car?

rwdaddict

Yes it does.

So I replaced both ignition coils and the temp sensor last night and still having the same issues. It does seem to run stronger and requires less throttle off the line so at least the parts weren't completely useless.

I'll take the ECU out this weekend and get pics. I still didn't jump the fuel ecu. Also I still haven't run the car with the MAF unplugged which would run the car on calculated loads and let me know if the MAF is still the culprit.

LScowboyLS

if you can't get the right angles in the photos to make the writing on all sides of the caps readable, just annotate the photos in MS paint with the numbers off of each cap. - I have seen many instances where rebuilders make mistakes of getting two caps switched into the wrong holes (kind of like mixing up two plug wires) or using the wrong values, wrong type of caps (always) or the polarity backwards.

rwdaddict

So I unplugged the AFM and all my stuttering problems went away. So I'm going to hunt down another AFM to test. Does anybody have a known working one for sale?

rwdaddict

Well finally had the chance to swap the AFM with a known working unit. It shifts perfect now, no more bucking or hesitation.

So the only thing left now is it's poor 0-60 times. I clocked about 11.5 seconds last night. Now i know she has 200k on it and i shouldn't expect the stock 7.5 but nearly 4 seconds when i have an intake and taking out the cats and resonator. I should be close to that 8.5-9 range. Thoughts?

OKSTANCE

ever had your throttle body cleaned?

shanjam

try and clean crank sensor

shanjam

try and clean crank sensor