94 LS400 - sluggish acceleration, and low RPM pinging

[och]

Welp, my timing belt and water pump replacement didn't do jack, except my water pump no longer leaks so the car doesn't overheat. It still pings and lags.

White LS, if you can be a little more specific about the cable, (I assume it's the throttle cable), and how exactly did you tighten it, I will try it on my car, and see if it does anything. However, I think if tightening cable does anything, it probably has to do with faulty TPS.

I'm probably going to try and hook up SAFC controller, and try playing with air/fuel ratios, and see if it improves anything. But thats not until a couple of month from now.

 

[White ls400]

OK here goes as i cant find a picture to explain better, There is a black cover that sits just behind the tb and partly over it, it has 2 cables coming from the left if looking at the car head on then there is a third cable that comes from the right and runs through a steel bracket and 2 nuts either side of the bracket..Undo the bolt on the left side first then tighten the one on the right side
There should be about 7mm of the thread showing when the bolt is adjusted correctly

 

[och]

OK here goes as i cant find a picture to explain better, There is a black cover that sits just behind the tb and partly over it, it has 2 cables coming from the left if looking at the car head on then there is a third cable that comes from the right and runs through a steel bracket and 2 nuts either side of the bracket..Undo the bolt on the left side first then tighten the one on the right side
There should be about 7mm of the thread showing when the bolt is adjusted correctly

The cable on the right is for cruize control. The throttle would be one of the two on the right.

 

[White ls400]

Yeah thats the one that autospeed.com website said to adjust... Anyway my pinging returned later on yesterday but no where near as bad so it may just be coincidence that it went away yesterday... So now i may just wait untill i get my exhaust done and see what happens... The longer its there the more it gets on your nerves hey!

 

[och]

Yeah thats the one that autospeed.com website said to adjust... Anyway my pinging returned later on yesterday but no where near as bad so it may just be coincidence that it went away yesterday... So now i may just wait untill i get my exhaust done and see what happens... The longer its there the more it gets on your nerves hey!

Keep us posted... maybe its clogged cats?

 

[White ls400]

Just researching soarer central forums about this, but one guy was complaining of the exact same issues and he said it ended up being a loose or disconnected airflow sensor, Is that just another name for the maf or a separate sensor?

 

[och]

Just researching soarer central forums about this, but one guy was complaining of the exact same issues and he said it ended up being a loose or disconnected airflow sensor, Is that just another name for the maf or a separate sensor?

Yeah, I think its the MAF.

 

[White ls400]

the soarercentral.com boys reckon it will most likely be cam angle sensor... Let me know if ya try this as i cant im broke

 

[och]

the soarercentral.com boys reckon it will most likely be cam angle sensor... Let me know if ya try this as i cant im broke

Well, there are two of these sensors, and I think they are just magnets. Doubt if they fail very often, if at all.

 

[White ls400]

Well mine ended up being simple it was the k&n replacement filter stirring things up for some undetermined reason at the moment

 

[och]

Well mine ended up being simple it was the k&n replacement filter stirring things up for some undetermined reason at the moment

Yeah, I had a K&N filter screw up the MAF in my GS430, but my LS has a brand new MAF and OEM filter.

 

[White ls400]

Hopefully its something as simple, like a loose clamp on the inlet, have you checked the rubber accordian lookin hose for splits?

 

[och]

So, I'm still "In Pursuit of Solution" to my problem, and I was browsing club lexus SC forums from the beginning, and I found this post in a thread about a problem similar to mine:

The low speed hesitation could also be attributed to the inherent bad fuel/timing maps built into the ECU from the factory. On early V-8s, low rpm/high load maps cause the engine to ping and activate the knock sensors which scale back the timing and reduce power. What you need is a way to add fuel during low rpm/high load conditions. During light to around 2/3 throttle, the ECU is in closed loop with the 02 sensors controlling fuel/air mixture. Above around 2/3 throttle, the ECU ignores the 02 signal and defaults to its own maps, which are poorly calibrated at low rpm.

There are several ways to get the car to run better... The best one I know of is to buy an Apexi S-AFC fuel computer to instruct the ECU to add or subtract fuel from the curve under these conditions. The S-AFC costs around $300-$325. The car will run alot better and may even make more top end power if you've got exhaust and intake mods.

Other solutions are:

Split-Second ARC $269
Simple box that Adjusts air/ fuel

Or the TSC1 $82, which fakes the coolant temp signal into thinking the engine is cooler and therefore adding more fuel to the maps.
(won't hurt normal fuel economy in closed loop).

www.splitsec.com

And then this post in a SAFC-II discussion thread:

That really pisses me off to see the stock ECU go 16.9 A/F at low rpm/ high throttle position. I suspected that the earlier V-8s went lean and was causing alot of pinging... NO WONDER!!!! Drivability should be 2x better with the A/F where it should be. I that situation, the knock sensors go off, it pulls timing then the whole thing basically bogs until around 4000rpm.

I had a 93 LS400 that would ping and bog until around 3500-4000rpm. Finally got so frustrated that I gave the car up. The dealer never helped. As suspected, this was the real reason. Lexus just didn't want to own up to it. I'd consider this $320 upgrade to be essential for any early SC or LS.

Seeing that SC300T is basically having describing my problems in his old post, I sent him a private message, describing my problem and looking for suggestions, and if using SAFC would be a possible solution, and he was kind enough to send me a reply.

I haven't followed this much lately, but yes your assumptions are correct.... Any device you can put in-line with the MAF, i.e. S-AFC to modify the amount of airflow the computer sees will trick the ECU into richening the mixture while open loop, i.e. above 2/3 throttle. It should fix your symptom.

One more thing... The reason that the car runs well when you pull the MAF lead to the ECU (and get CEL), is that the ECU is defaulting to a base fuel map. The maps that are stored are gradually changed by the ECU. There is a long term and short term fuel trim function that constantly is changing the map. Apparently, as LS400 vehicle wear, this trim function of the fuel map in the ECU is wanting the mixture leaner and leaner.

You'll also notice that if you drive in cold conditions just after startup when the engine is not yet fully warm, if you really get on it, the engine will have plenty of power. This is because the fuel trim isn't taking out as much fuel when the engine is cold, and the ECU wants the engine to run a little richer. Try an S-AFC used on ebay or something. Isn't that expensive. I think you'd like the results.

Its the ECU programming that is at fault. A new ECU will still learn the same thing. These engines didn't do that new from the factory - there is something as the car ages that causes leaning.

For your application, any simple fuel controller that will add fuel (by manipulating the MAF signal) will work.

 

[LS400GUY]

Och:

please let us know if and when you install the SAFC-II, I'm having the same problem as you with the sluggishness, and I've done most of everything you've done with my '95 LS400, I only have 123k miles and bought it a year ago w/107k miles but the previous owner never changed the air filter (it was "disgustingly" dirty). I'd immediately changed tb & related bearings, wp, tenioner, cam & crank seals, plugs(repl. w/iridium), wires, caps/rotors, tranny flush repl w/Amsoil 100 syn oil, use ONLY Castrol Syntec motor oil, and I'm a big believer in Marvel mystery oil in the crankcase and gas., repl both primary o2 sensors. While the pickup is drastically improved after all of this, I still think it should have much quicker p/u with 260 horses pushing it. Huge difference in p/u from my '98 LS400, of course that one has VVTI. Should my attn be centered on the MAF? I truly believe with it running with a dirty and clogged air filter for maybe 50k miles or more is contributing to the sluggishness and high idle speed upon start-up (high idle goes to normal after a few minutes). If anyone else can offer suggestions, it would be greatly appreciated. Cheers.

LS400GUY

 

[och]

Och:

please let us know if and when you install the SAFC-II, I'm having the same problem as you with the sluggishness, and I've done most of everything you've done with my '95 LS400, I only have 123k miles and bought it a year ago w/107k miles but the previous owner never changed the air filter (it was "disgustingly" dirty). I'd immediately changed tb & related bearings, wp, tenioner, cam & crank seals, plugs(repl. w/iridium), wires, caps/rotors, tranny flush repl w/Amsoil 100 syn oil, use ONLY Castrol Syntec motor oil, and I'm a big believer in Marvel mystery oil in the crankcase and gas., repl both primary o2 sensors. While the pickup is drastically improved after all of this, I still think it should have much quicker p/u with 260 horses pushing it. Huge difference in p/u from my '98 LS400, of course that one has VVTI. Should my attn be centered on the MAF? I truly believe with it running with a dirty and clogged air filter for maybe 50k miles or more is contributing to the sluggishness and high idle speed upon start-up (high idle goes to normal after a few minutes). If anyone else can offer suggestions, it would be greatly appreciated. Cheers.

LS400GUY

High idle upon start up is absolutely normal, in fact its necessary. When the car is cold it idles higher, then once it warms up the idle settles down at 650rpms.

Check your MAF and TPS, try running it with MAF disconnected, see what happens.

 

[White ls400]

well my pingings gone and i can only attribute it to 2 things that were replaced and its either the coolant temp sensor or all new inlet manifold gaskets

 

[LS400GUY]

High idle upon start up is absolutely normal, in fact its necessary. When the car is cold it idles higher, then once it warms up the idle settles down at 650rpms.

Check your MAF and TPS, try running it with MAF disconnected, see what happens.

Exactly where is the MAF located? Without a shop manual, I want to make sure its the right device. Thanks.

 

[White ls400]

just behind the airbox it has an aluminium body with a black sensor on top

 

[LS400GUY]

thanks white LS..., but do you know if any pics are available on previous threads?

 

[och]

First gen (90-94) and second gen (95-97) LS400's have completely different ECU's and MAFs, although they are in the same place. You maf should be right after the filter housing on your intake, its a black thingy with a plug.