94 LS400 - sluggish acceleration, and low RPM pinging

[och]

So I've had my 1994 LS400 for a year now, and it's suffering from sluggish acceleration (takes 14 seconds to get from 0 to 60), and it pings when cruising at 1200-1400 RPMs. At these RPMs the pinging is constant, but it also pings on gear changes during hard acceleration, and I hear occasional pings during hard acceleration at upper RPM ranges as well. The car right now has around 110K miles on the clock. I've been trying to resolve this situation for the longest time, and I've done numerous thing, and so far nothing has worked. Here's whats been done so far:

1) Timing belt service done at 80K according to the sticker on the engine (by previous owner).
2) Used numerous fuel system cleaners, such as Techron, Lucas.
3) Used SeaFoam in gas tank, crankcase, and intake chamber (total of three treatments).
4) Replaced fuel filter.
5) Removed and cleaned throttle body - helped to resolve low idle issues.
6) Bypassed powersteering idle up valve - completely resolved low idle issues.
7) Cleaned idle air control valve.
8) Did a full tune up, including new air filter, new spark plugs, new ignition wires, new distributor caps and rotors.
9) Replaced TPS (wasted money on changing from good to new).
10) Replaced passenger side ignition coil (wasted money on changing from good to new).
11) Replaced both main oxygen sensors.
12) Both EGR delete kit, and blocked the EGR system. It made the low RPM pinging even worse, with no power gains, so I removed it.
13) Cleaned PCV valve.
14) Replaced the MAF sensor (going to be returning the new MAF sensor next week, as it's very expensive, and made no difference).

All of this, and with no avail. Of course the car is running very smooth with all that tuning, and the only money I have really wasted, were the TPS and ignition coil, which defenately didn't need to be replaced. I'm going to return the MAF sensor for a refund, and I'm still going to re-install the EGR block off kit once I resolve whatever the issue I'm having.

But this is where it gets interesting. I've been learning the patterns for a while now, and this is what I notice. When the engine is cold, it performs very well, doesn't ping and has quite a bit of pick up, and the colder it is outside, the better it performs. Once warmed up however, it lags no matter what the outside temperature is. The temperature gauge shows normal temperature, so the engine isn't overheating. The other thing is, if I completely disconnect the MAF sensor, when the engine is still cold, it has so much torque that it's comparable to my GS430, it will easily spin tires when punched from a dead stop, and will probably make 0-60 in 7-8 seconds, like it's suposed to. However once the car is warmed up, it starts to lag, and ping harder than when the MAF is connected. Interestingly enough, with disconnected MAF it does not ping when cruising at 1200-1400 rpms, but pings hard whenever accelerating. All of that led me to believe my MAF was malfunctioning, so I replaced it with a brand new unit, which made no difference whatsoever. Therefore, I'm going to be returning the MAF, and trying to further investigate the problem. Right now I'm out of clue what could be causing this, here's my theories.

Bad fueld pump? Bad injectors? Bad ECU? Clogged exaust? Worn out, tired engine? All of these theories do not stand when considering that the car runs well while the engine is cold. I'm pretty sure I'm having a problem with fuel/air mixture, but I'm trying to figure out what may be causing it. With new MAF and O2 sensors, what else can I check?

 

[rms]

Take it to a dealer and get an ecu error code check. Would be a lot cheaper than what you have already spent.

Seems related to engine temp. There are 2 temp sensors, 1 brown 1 green.

 

[gloverman]

It is possible to check codes with a split pin or steel paper clip simply bridge Te1 and E1 in the diagnostic box and count the flashes of the engine check light, slow flashes for 10s and fast flashes for 1s with a gap in between.
Have you tested the mixture , fuel flow and pressure and checked the ignition base timing? These may give a clue to the problem
Cheers

 

[och]

Take it to a dealer and get an ecu error code check. Would be a lot cheaper than what you have already spent.

Seems related to engine temp. There are 2 temp sensors, 1 brown 1 green.

Isn't the check engine light suposed to be on if there are any error codes? And can you please elaborate on the temperature sensors? The temperature gauge shows normal temperature, the coolant level is fine, and radiator fans seem to work fine as well. Is one of these sensors sending the temperature signal to the gauge and the other one to the ECU?

 

[och]

It is possible to check codes with a split pin or steel paper clip simply bridge Te1 and E1 in the diagnostic box and count the flashes of the engine check light, slow flashes for 10s and fast flashes for 1s with a gap in between.
Have you tested the mixture , fuel flow and pressure and checked the ignition base timing? These may give a clue to the problem
Cheers

Haven't tested any of these, I assume I need to take it a dealer or a good diagnostics shop to get it done?

 

[rms]

Isn't the check engine light suposed to be on if there are any error codes? And can you please elaborate on the temperature sensors? The temperature gauge shows normal temperature, the coolant level is fine, and radiator fans seem to work fine as well. Is one of these sensors sending the temperature signal to the gauge and the other one to the ECU?

Most sensors will read to 150 deg C before going out of range so the ECU may not see a faulty temp sensor. Actual engine could be 90c but ECU is seeing 120c? and leaning mixture to suit. Knock sensors can only pull a certain amount of timing out so it pings, no power ???

Don't know which temp sensor does what.

A real time scan tool can give the engine data as you drive. If there is a high quality workshop that has real time scanning capability I would search them out.

 

[och]

Most sensors will read to 150 deg C before going out of range so the ECU may not see a faulty temp sensor. Actual engine could be 90c but ECU is seeing 120c? and leaning mixture to suit. Knock sensors can only pull a certain amount of timing out so it pings, no power ???

So that means I wont be able to pull error codes, right?

Don't know which temp sensor does what.

A real time scan tool can give the engine data as you drive. If there is a high quality workshop that has real time scanning capability I would search them out.

I'm going to try and find a good quality trustworthy diagnostics shop. I once went to a diagnostics shop nearby with my GS430, because it was pinging, and was ripped off out of $500, they lied to me that they had to re-program the ECU. I later found out that the ECU could not be reprogrammed by anyone but Lexus dealer, and the pinging came back. It turned out that a dirty MAF was causing it, because I had a K&N filter, the MAF had oil all over it, and $3 spray can of electrical cleaner resolved the issue. So basically I don't really trust these diagnostics shops.

 

[och]

My other idea, is if everything else fails, is to get one of these Apexi SAFC's, and tune the air/fuel mix.

 

[och]

Welp, just went to Autozone, picked up a coolant temperature sensor, and replaced it. No change.

 

[Lextreme II]

Reprogrammed ECU???? WOW... Time for a small claim court....

 

[och]

Reprogrammed ECU???? WOW... Time for a small claim court....

Yeah, I wish I still had the receipt... I paid cash too, so I have no proof.

 

[och]

I'm also thinking, since the engine is running beautifully when cold, maybe once it warms up for whatever reason its running internally too hot, and even thought the coolant temperature is normal, the engine overheats internally, starts pinging, and knock sensors retard the timing, thus it loses power? Should I try a low temp thermostat?

 

[White ls400]

anyone found an answer to this problem yet cause is starting to get on my nerves too

 

[White ls400]

cas related?

 

[och]

No cigar just yet, but I'm in the middle of timing belt/water pump replacement, so once I finish lets see what that brings.

 

[White ls400]

Well iv had my mechanic look over my car and said its deffinatly pinging and the knock sensors would never pick it up because they dont come into range untill about 1800rpm and he even proved it by tapping on the heads and the motor doesnt even flinch. He thinks it could be related to either the air temp sensor(anyone know of problems with these or maybe even value of these) or the running temp of the car

 

[och]

Well iv had my mechanic look over my car and said its deffinatly pinging and the knock sensors would never pick it up because they dont come into range untill about 1800rpm and he even proved it by tapping on the heads and the motor doesnt even flinch. He thinks it could be related to either the air temp sensor(anyone know of problems with these or maybe even value of these) or the running temp of the car

Your air temp sensor is actually integrated into your MAF, and it changes resistance with varying weather. I thought of that too, and I even tried tricking the ECU into thinking it was hotter or colder outside by splitting the wire from the sensor and putting different resistors in there - No cigar.

I also think it may be temperature related, because I think my engine was running too hot, because everything under the hood was getting very hot to the touch. But then the temperature gauge always showed normal temperature, until it started overheating recently, and now I am replacing the water pump and timing belt. I'm almost done with the repair, and possibly will have it all back together by tomorrow. I'll do the coolant flush, and see how it runs, and if anything has changed, and I'll post here. If your mechanics figures something out, please report back.

 

[White ls400]

Just a long shot och, but have you ever had any problems that may of caused the exhaust too heat up, because i started too notice the pinging after i had a severe misfire which led too the left cat to get incredibly way too hot and i was wondering if it was possible if maybe it could be too do with partially blocked cats.

 

[och]

Just a long shot och, but have you ever had any problems that may of caused the exhaust too heat up, because i started too notice the pinging after i had a severe misfire which led too the left cat to get incredibly way too hot and i was wondering if it was possible if maybe it could be too do with partially blocked cats.

I don't know but I'm not the first owner of the car. Usually cats getting red hot is a condition when you're not getting spark, and all the fuel gets dumped into the exaust. It's often caused by bad ignition coil. However it's an interesting theory, if I finally get my timing belt done and the car still persists with the old problems, I'll look into that.

 

[White ls400]

Ok, today i have been thinking whats different on my car to before it started pinging, Then i remembered after reading that www.autospeed.com article about the cable that runs into the black cover that sits over the tb that you can tighten to increase your gearbox line pressure, Well anyway i loosened that off back to factory settings and the pinging is gone, i dont know if its gone for good or even just a coincedence because i only went for a 20 minute drive but I didnt ping at all and its about 26'c day here and thats usually when its the loudest