NEED HELP - '93 LS400 surging badly and huge power loss
02-23-20, 04:50 AM
#16
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Alright folks, I'm back again. My ailing 1993 LS400 keeps getting worse. I thought it had exhaust leaks, but it was just oil smoking on the exhaust manifolds after the car sat for too long. The EGR valve leaked badly, so I blocked it off with a piece of exhaust gasket - it is no longer possible to buy new EGR valves for the first-gen Cali models, along with most of the other Cali-specific parts. This, unfortunately, solved nothing. I sent my ECU in to be fixed - almost no change in how the car ran. I replaced the injectors with new ones - nothing.
I'm getting really tired of driving the tortured thing every day.
Occasionally, it'll have plenty of power - not nearly as much as it did when I purchased it, but enough to be passable. Then, it'll lose enough after a stoplight (or just randomly) that it takes me 20 seconds or more to get up to 40mph - I can't press the pedal down much more than half, because if I do, the engine will surge and then immediately try to stall in rapid succession, over and over again, until I let off the gas. After it stops doing this, it manages to lose even more power. Then, randomly during the drive, it'll go back to having a passable amount of power. Sometimes it'll surge lightly while cruising. The engine will also make a groaning noise while it's low on power. It's not the ignition coils, the spark plugs, or the wires - wires and plugs are new, and I tested both of the coils by temporarily replacing them with a new coil. This also changed nothing. The fuel pump is new as well, and the filter only has about 2k miles on it. Fuel pressure is within spec (44psi IIRC). Air filter is new. Battery is new. Alternator is fine, the P/S system leaks but not near the alternator, and I've tested it as well. I've ordered an OBD1-OBD2 adapter so I can take it for a drive and see if anything looks wrong, but last time I did this (only idling because the only OBD1 reader I had access to had a failed battery) nothing looked out of the ordinary. I am, as always, completely out of ideas.
I'm getting really tired of driving the tortured thing every day.
Occasionally, it'll have plenty of power - not nearly as much as it did when I purchased it, but enough to be passable. Then, it'll lose enough after a stoplight (or just randomly) that it takes me 20 seconds or more to get up to 40mph - I can't press the pedal down much more than half, because if I do, the engine will surge and then immediately try to stall in rapid succession, over and over again, until I let off the gas. After it stops doing this, it manages to lose even more power. Then, randomly during the drive, it'll go back to having a passable amount of power. Sometimes it'll surge lightly while cruising. The engine will also make a groaning noise while it's low on power. It's not the ignition coils, the spark plugs, or the wires - wires and plugs are new, and I tested both of the coils by temporarily replacing them with a new coil. This also changed nothing. The fuel pump is new as well, and the filter only has about 2k miles on it. Fuel pressure is within spec (44psi IIRC). Air filter is new. Battery is new. Alternator is fine, the P/S system leaks but not near the alternator, and I've tested it as well. I've ordered an OBD1-OBD2 adapter so I can take it for a drive and see if anything looks wrong, but last time I did this (only idling because the only OBD1 reader I had access to had a failed battery) nothing looked out of the ordinary. I am, as always, completely out of ideas.
02-23-20, 09:33 PM
#17
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02-23-20, 11:19 PM
#18
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02-24-20, 09:23 AM
#19
Pole Position
02-24-20, 09:48 AM
#20
I don't remember all the details without looking up the years, but you should be careful about exactly what year the people giving you advice are talking about.
My '91, and at least from 90-94, I know they were not MAF (with a hot wire or film), they were a Karman Vortex sensor, referred to as an AFM (air flow meter, without the word "mass" in there). The MAF (mass air flow) sensor is based on a sensing method that measures mass flow directly, without need for thermal density compensation that the MAF needs. So that's why "mass" is in the name for MAF, but not AFM.
At some point after that, might have been 95, might have been later, they switched to the more common hot wire/film ones.
Those two sensing methods are completely different, and require/tolerate different types of cleaning, if any.
So be careful if you get advice from someone that may be correct for their AFM, but not for your MAF. And in general, for any car, these sensors are relatively delicate and easy to screw up when cleaning. So don't fire up the pressure washer just yet.
Here's a post I wrote a while ago about the two basic types.
https://www.clublexus.com/forums/ls-...l#post10206613
My '91, and at least from 90-94, I know they were not MAF (with a hot wire or film), they were a Karman Vortex sensor, referred to as an AFM (air flow meter, without the word "mass" in there). The MAF (mass air flow) sensor is based on a sensing method that measures mass flow directly, without need for thermal density compensation that the MAF needs. So that's why "mass" is in the name for MAF, but not AFM.
At some point after that, might have been 95, might have been later, they switched to the more common hot wire/film ones.
Those two sensing methods are completely different, and require/tolerate different types of cleaning, if any.
So be careful if you get advice from someone that may be correct for their AFM, but not for your MAF. And in general, for any car, these sensors are relatively delicate and easy to screw up when cleaning. So don't fire up the pressure washer just yet.
Here's a post I wrote a while ago about the two basic types.
https://www.clublexus.com/forums/ls-...l#post10206613
02-24-20, 01:42 PM
#21
Pole Position
I don't remember all the details without looking up the years, but you should be careful about exactly what year the people giving you advice are talking about.
My '91, and at least from 90-94, I know they were not MAF (with a hot wire or film), they were a Karman Vortex sensor, referred to as an AFM (air flow meter, without the word "mass" in there).
At some point after that, might have been 95, might have been later, they switched to the more common hot wire/film ones.
So be careful if you get advice from someone that may be correct for their AFM, but not for your MAF. And in general, for any car, these sensors are relatively delicate and easy to screw up when cleaning. So don't fire up the pressure washer just yet.
Here's a post I wrote a while ago about the two basic types.
https://www.clublexus.com/forums/ls-...l#post10206613
My '91, and at least from 90-94, I know they were not MAF (with a hot wire or film), they were a Karman Vortex sensor, referred to as an AFM (air flow meter, without the word "mass" in there).
At some point after that, might have been 95, might have been later, they switched to the more common hot wire/film ones.
So be careful if you get advice from someone that may be correct for their AFM, but not for your MAF. And in general, for any car, these sensors are relatively delicate and easy to screw up when cleaning. So don't fire up the pressure washer just yet.
Here's a post I wrote a while ago about the two basic types.
https://www.clublexus.com/forums/ls-...l#post10206613
) I didn't have time earlier to look it up but I wanted to tell the OP not to clean it. I think it was 95 they switched to MAF, but like ya said, it could have been later. The OP has a 93 so his is an AFM. That is a nice descriptive post ya have in the other thread. I knew it was there somewhere and would be found with a search. 
02-29-20, 07:37 PM
#22
Pit Crew
Thread Starter
Thanks oldskewel for the explanation. For the life of me I couldn't remember "Karman Vortex". (Must be gettin old ) I didn't have time earlier to look it up but I wanted to tell the OP not to clean it. I think it was 95 they switched to MAF, but like ya said, it could have been later. The OP has a 93 so his is an AFM. That is a nice descriptive post ya have in the other thread. I knew it was there somewhere and would be found with a search.
) I didn't have time earlier to look it up but I wanted to tell the OP not to clean it. I think it was 95 they switched to MAF, but like ya said, it could have been later. The OP has a 93 so his is an AFM. That is a nice descriptive post ya have in the other thread. I knew it was there somewhere and would be found with a search. The AFM, as I now know it's called, is fine. I discovered this by buying another unit and testing it. The car has the same issues. Still refuses to throw a code. Gets up to about 3000rpm under heavy load, and then immediately tries to force a stall. Stopped the car almost entirely from about 25mph. When it goes into limp mode, it runs fine. I have an OBD2 adapter for the under-dash plug now, so I can hook a scan tool to it, I just haven't had the time. Not sure how much it'll help as I know the ECU doesn't report a whole lot of things to the scan tool.
03-01-20, 09:43 PM
#23
Pit Crew
Thread Starter
I advanced the TPS before driving to work this morning, (yes I know that's supposed to be done with feeler gauges) and the car responded very well to that, for some reason. Still has the same problems but they aren't as severe.
03-12-20, 12:46 AM
#24
Pit Crew
Thread Starter
Alright, so I can no longer take the car on the freeway as it can't really hold 60-70mph. I replaced the coolant temp sensor (yes, the one with two wires), and that helped for a little bit - but then it started running leaner and leaner again. I have no idea why, but it seems like the ECU is doing this on purpose. I'm going to head down to pick n' pull on my next day off to grab a second ECU off a '93 and see if it changes anything - @Yamae , are the ECUs the same between 1993 california and regular models?
03-12-20, 03:11 AM
#25
Moderator
@Yamae , are the ECUs the same between 1993 california and regular models?
03-12-20, 08:22 AM
#26
Pole Position
I'm not an ECU guru like Yamae but he's correct, not the same, but......
This is from my experience when I was looking for an ECU for my 94:
You can use a Ca spec ECU in a Fed spec car but not the other way around. From what I researched was the only difference is the Ca spec car has an extra air pump on the engine. (I never found out what it does exactly) Something to do with emissions. I've read on here someone used a Ca spec for a Fed spec car and it worked fine. It might just throw a code for the air pump cuz it's not even on the car.
I got mine from a junkyard car which originally was a Ca. car but moved to Kentucky and eventually ended up here in Ct. When I pulled the ECU it was a Fed spec. It was a running car when I pulled it.
This is from my experience when I was looking for an ECU for my 94:
You can use a Ca spec ECU in a Fed spec car but not the other way around. From what I researched was the only difference is the Ca spec car has an extra air pump on the engine. (I never found out what it does exactly) Something to do with emissions. I've read on here someone used a Ca spec for a Fed spec car and it worked fine. It might just throw a code for the air pump cuz it's not even on the car.
I got mine from a junkyard car which originally was a Ca. car but moved to Kentucky and eventually ended up here in Ct. When I pulled the ECU it was a Fed spec. It was a running car when I pulled it.
03-12-20, 10:01 AM
#27
Pit Crew
Thread Starter
No, the California and the federal ECU are not the same. See the lower part of this post. https://www.clublexus.com/forums/ls-...ml#post7496164
03-12-20, 01:25 PM
#28
Lexus Champion
Then run donor vehicle VIN through Lexus database to insure the yard is not providing you with a random VIN for ECU.
Have vendor agree in writing that your technician be allowed to open the ECU to inspect the Circuit board for damage from leaking electrolyte from capacitors..which, if original, is possibile.
Good luck.
03-15-20, 12:50 AM
#29
Pit Crew
Thread Starter
The way to work this is to contact yards who have already extracted the ECU (and have not opened it). Inquire of the VIN # of the donor vehicle and image of the ECU P.N. (cross check that ECU is correct P.N. from that donor vehicle..)
Then run donor vehicle VIN through Lexus database to insure the yard is not providing you with a random VIN for ECU.
Have vendor agree in writing that your technician be allowed to open the ECU to inspect the Circuit board for damage from leaking electrolyte from capacitors..which, if original, is possibile.
Good luck.
Then run donor vehicle VIN through Lexus database to insure the yard is not providing you with a random VIN for ECU.
Have vendor agree in writing that your technician be allowed to open the ECU to inspect the Circuit board for damage from leaking electrolyte from capacitors..which, if original, is possibile.
Good luck.
03-15-20, 01:48 AM
#30
Moderator
2000 rpm MAX?
Sounds like it's a limp home mode. The confirmation can be done checking the fire timing. It is fixed and there is no advancement.
Sounds like it's a limp home mode. The confirmation can be done checking the fire timing. It is fixed and there is no advancement.