SOS! Please Help, GS400 running VERY ROUGH
08-20-14, 07:56 AM
#1
Driver School Candidate
Thread Starter
Join Date: Jun 2014
Location: Florida
Posts: 49
Likes: 0
Received 0 Likes
on
0 Posts
SOS! Please Help, GS400 running VERY ROUGH
Hello fellows, this is my first post on this great forum, and the GS400, my first Lexus.... 
A few months ago I came across this mint 1999 GS400 with a blown engine. I contacted the owner, bought the car, got a JDM engine and transmission (1UZ-FE) and in put it into the car.
Even though I have experience with EFI, including stand-alone installations and programming, I am stumped..... Here the symptoms:
1- When cranked, the engine starts right up, revs up to maybe 1500 rpm (all gauges are dead, that`s another ghost to hunt...) and stalls. I am sure all 8 cylinders are firing since it feels and sounds smooth for that short amount of time (about 2 seconds maybe)
2- If you press the gas pedal to avoid stalling, it rus very rough, maybe on 4 or 5 cylinders. The spark plugs get dark and the OBD2 scanner says P0300 (Ramdom missfire).
3- I kept it running for about 10 minutes at about 2000 RPM until the engine warmed up. Nothing changed. My scanner doesn´t let me see 02 sensor voltages.
Measures taken:
1- Checked fuel pressure. I don`t have a gauge, but I get a strong spray out of the feed hose.
2- Replaced the battery. (New)
3- Cleaned the MAF sensor
4- Replaced the injector seals and tested for vaccum leaks. (No leaks)
5- Double checked all wiring connectors
6- Checked the ignition coils (all firing)
7- Checked compression (180-190 psi all cylinders)
8- Checked cam timing (All marks aligned)
9- Tested with the JDM ECU that came with the engine. Starts as quicky but can`t keep it running by opening the throttle. (And it won`t communicate with my cheap scanner)
I`ve tried finding the wiring diagram on the web with no luck. There is this plug close to ignition coil #7 (behind the intake resonator) that I don`t know what its for. Hard for me to believe the problem is a bad sensor since it does start smoothly for 2 seconds and then goes rough. I am suspecting the wiring or the ECU.
Any clues???
Thank you.
- Angelo
99 GS400
Panama (Central America)
A few months ago I came across this mint 1999 GS400 with a blown engine. I contacted the owner, bought the car, got a JDM engine and transmission (1UZ-FE) and in put it into the car.
Even though I have experience with EFI, including stand-alone installations and programming, I am stumped..... Here the symptoms:
1- When cranked, the engine starts right up, revs up to maybe 1500 rpm (all gauges are dead, that`s another ghost to hunt...) and stalls. I am sure all 8 cylinders are firing since it feels and sounds smooth for that short amount of time (about 2 seconds maybe)
2- If you press the gas pedal to avoid stalling, it rus very rough, maybe on 4 or 5 cylinders. The spark plugs get dark and the OBD2 scanner says P0300 (Ramdom missfire).
3- I kept it running for about 10 minutes at about 2000 RPM until the engine warmed up. Nothing changed. My scanner doesn´t let me see 02 sensor voltages.
Measures taken:
1- Checked fuel pressure. I don`t have a gauge, but I get a strong spray out of the feed hose.
2- Replaced the battery. (New)
3- Cleaned the MAF sensor
4- Replaced the injector seals and tested for vaccum leaks. (No leaks)
5- Double checked all wiring connectors
6- Checked the ignition coils (all firing)
7- Checked compression (180-190 psi all cylinders)
8- Checked cam timing (All marks aligned)
9- Tested with the JDM ECU that came with the engine. Starts as quicky but can`t keep it running by opening the throttle. (And it won`t communicate with my cheap scanner)
I`ve tried finding the wiring diagram on the web with no luck. There is this plug close to ignition coil #7 (behind the intake resonator) that I don`t know what its for. Hard for me to believe the problem is a bad sensor since it does start smoothly for 2 seconds and then goes rough. I am suspecting the wiring or the ECU.
Any clues???
Thank you.
- Angelo
99 GS400
Panama (Central America)
Last edited by PTYGS400; 08-20-14 at 08:02 AM.
08-20-14, 03:56 PM
#2
Driver School Candidate
Thread Starter
Join Date: Jun 2014
Location: Florida
Posts: 49
Likes: 0
Received 0 Likes
on
0 Posts
Update: SOS! Please Help, GS400 running VERY ROUGH
Hello fellows. Update. The engine is still missing heavily and dies as soon as you let off the gas. The curious part is that it does get smooth for very short periods. I took it for a drive around the block and it stalled many times, no power, no power and at one point it went smooth and chirped the tires. Listening to the exhausts it sounds like a lean missfire, no smoke, no bad smell but missing heavily.
I also tried leaning out the mixture by loosening the maf sensor and letting in different amounts of false air (because I have black spark plugs). It did not improve anything. I`ve thought of running another test by removing the fuel pump fuse and try feeding the engine with a spray bottle ("manual carburetor"). This way I could isolate fuel from ignition problems.
I would greatly apreciate any ideas.
Thanks in advance.
- Angelo
99 GS400
I also tried leaning out the mixture by loosening the maf sensor and letting in different amounts of false air (because I have black spark plugs). It did not improve anything. I`ve thought of running another test by removing the fuel pump fuse and try feeding the engine with a spray bottle ("manual carburetor"). This way I could isolate fuel from ignition problems.
I would greatly apreciate any ideas.
Thanks in advance.
- Angelo
99 GS400
08-21-14, 06:20 AM
#6
Pole Position
+1 for that, hes the clublexus genius. Seems to know more about these cars then anyone I ever came across. Why dont you start with the plugs if it has black plugs, that can only help.
08-21-14, 07:13 AM
#7
Driver School Candidate
Thread Starter
Join Date: Jun 2014
Location: Florida
Posts: 49
Likes: 0
Received 0 Likes
on
0 Posts
I did replace the spark plugs, no change.
Here is a short clip:
Thank you guys!
Trending Topics
08-21-14, 07:17 AM
#8
Pole Position
Is the random misfire the only code? Are they any codes pending or OEM specific codes? Do you have a generic scanner or something that can dig more into the Toyota OBD? Might have to borrow one from somebody.
Also you say you can't query the O2 sensors. You may be missing your sensor feed and none are reporting to the ECU.
Test to make sure your 5v line is up by verifying 5v at the misc. sensors (not O2). O2 heater circuits should show 12v but these don't matter for this issue. Typically these are the black wires, or the two that are the same color.
Your dead gauges may be more related than you think.
You really need to get your hands on the wiring manual.
All being said, my money is on a bad ground. Make sure ALL GROUNDS ARE CONNECTED and tight with no corrosion. This is critical.
While you're at it, check all fuses.
Report back and good luck!
Also you say you can't query the O2 sensors. You may be missing your sensor feed and none are reporting to the ECU.
Test to make sure your 5v line is up by verifying 5v at the misc. sensors (not O2). O2 heater circuits should show 12v but these don't matter for this issue. Typically these are the black wires, or the two that are the same color.
Your dead gauges may be more related than you think.
You really need to get your hands on the wiring manual.
All being said, my money is on a bad ground. Make sure ALL GROUNDS ARE CONNECTED and tight with no corrosion. This is critical.
While you're at it, check all fuses.
Report back and good luck!
08-21-14, 07:21 AM
#9
Pole Position
After seeing the video, I am also going to throw bad gas out there.
When did you last fill the tank? Did this gas come with car? You bought this car with a blown motor, how long was it sitting like this with that gas in it?
If that's the gas that came with the car, then drain the tank and refill with fresh.
When did you last fill the tank? Did this gas come with car? You bought this car with a blown motor, how long was it sitting like this with that gas in it?
If that's the gas that came with the car, then drain the tank and refill with fresh.
08-21-14, 07:49 AM
#10
Driver School Candidate
Thread Starter
Join Date: Jun 2014
Location: Florida
Posts: 49
Likes: 0
Received 0 Likes
on
0 Posts
Thank you Jose!
I have homework for tonite!
I can borrow a better scanner, another thing to do.
About the fuel issue. I put about 4 gallons of fresh gas in the tank since it seemed to have no gas (no gas out of the fuel hose while cranking). I have been suspecting fuel quality too... Maybe I will have to remove the fuel pump and take a look inside the tank... or maybe collect some gas from the fuel hose that feeds the rails and take a look at it. The car had been sitting for 8 months.
I have homework for tonite!
I can borrow a better scanner, another thing to do.
About the fuel issue. I put about 4 gallons of fresh gas in the tank since it seemed to have no gas (no gas out of the fuel hose while cranking). I have been suspecting fuel quality too... Maybe I will have to remove the fuel pump and take a look inside the tank... or maybe collect some gas from the fuel hose that feeds the rails and take a look at it. The car had been sitting for 8 months.
08-21-14, 08:03 AM
#11
Pole Position
Sounds like a plan. Also check for water in the tank. It doesn't mix with gas and is heavier so it sinks to the bottom. If there's water, you can siphon it out by placing a hose at the bottom and sucking it out until the water stops and only fuel is coming out. A hose with a jiggle ball valve is perfect for this. You can find these in boat supply stores.
Let us know what you find!
Let us know what you find!
Thank you Jose!
I have homework for tonite!
I can borrow a better scanner, another thing to do.
About the fuel issue. I put about 4 gallons of fresh gas in the tank since it seemed to have no gas (no gas out of the fuel hose while cranking). I have been suspecting fuel quality too... Maybe I will have to remove the fuel pump and take a look inside the tank... or maybe collect some gas from the fuel hose that feeds the rails and take a look at it. The car had been sitting for 8 months.
I have homework for tonite!
I can borrow a better scanner, another thing to do.
About the fuel issue. I put about 4 gallons of fresh gas in the tank since it seemed to have no gas (no gas out of the fuel hose while cranking). I have been suspecting fuel quality too... Maybe I will have to remove the fuel pump and take a look inside the tank... or maybe collect some gas from the fuel hose that feeds the rails and take a look at it. The car had been sitting for 8 months.
08-21-14, 11:02 PM
#15
Driver School Candidate
Thread Starter
Join Date: Jun 2014
Location: Florida
Posts: 49
Likes: 0
Received 0 Likes
on
0 Posts
Update: Aug 21
Update. Worked on the car for 4 hours this evening. Here is what I found:
1- Fuel tank inspection: to my surprisse the tank is almost full, I see no traces of water and the gas smells normal. The fuel tank internal surfaces are inmaculate. Could not get the fuel pump out, there is this hose attached to it that I did not want to mess with. I also removed the passanger`s side float, and took a one gallon gasoline sample in a can (maybe I can test this gas on something else)
https://www.dropbox.com/s/c1mvsst7kk...00696.jpg?dl=0
https://www.dropbox.com/s/wt7h2j1n4j...00697.jpg?dl=0
I put everything back together in the fuel tank area and moved to the engine bay...
2- Fuse inspection. All fuses look like new, seems like I am the first person to mess with them. All stock fuses, no findings here...
3- Loose plugs: one by the PS pump
https://www.dropbox.com/s/1yilm1p6lg...00701.jpg?dl=0
And the other one by cyl #7, close to the fuel rail:
https://www.dropbox.com/s/ur7rlwp2ll...00702.jpg?dl=0
4- Loose ground hunting: I found the fans to be hard wired to the ignition switch, both of them. Removed the relays to make them stop. Could this affect something else? Are fans controlled by a thermoswitch or by the ECU? All grounds behind the engine seem fine, and there is one from the manifold to the firewall. I kept looking and found this:
https://www.dropbox.com/s/3mbrkpymu1...00700.jpg?dl=0
Thats the negative battery cable, grounding the body close to the P/S pump. I was excited about this finding. Took me quite a while to untangle the wires so I could fasten this to the body, had to remove the battery, battery tray, airbox, intake resonator, etc. In this area I also found the P/S vaccum lines disconected.
I put everything back together, grounding point throughly scraped with a file and lubricated for rust protection and then tightly fastened with a clean bolt. I was anxious....
Started the car and got the very same sick missfire.
When the RPMs get very low, the intake starts backfiring and eventually dies if the throttle is not opened further. This beast sounds lean.... but the spark plugs get dark....
The 12V mod is a good idea. I need to hook up a fuel pressure gauge and get real info. I wanted to spray the intake with carb cleaner to see if it would clear up by adding fuel, but I didn`t have a helper to keep the engine running while I sprayed the intake.
I am tired, its almost 1 am. Keep the good ideas coming, I am far from defeated.... yet.
Tomorrow: fuel pressure...
Thank you all!
- Angelo
99 GS400
1- Fuel tank inspection: to my surprisse the tank is almost full, I see no traces of water and the gas smells normal. The fuel tank internal surfaces are inmaculate. Could not get the fuel pump out, there is this hose attached to it that I did not want to mess with. I also removed the passanger`s side float, and took a one gallon gasoline sample in a can (maybe I can test this gas on something else)
https://www.dropbox.com/s/c1mvsst7kk...00696.jpg?dl=0
https://www.dropbox.com/s/wt7h2j1n4j...00697.jpg?dl=0
I put everything back together in the fuel tank area and moved to the engine bay...
2- Fuse inspection. All fuses look like new, seems like I am the first person to mess with them. All stock fuses, no findings here...
3- Loose plugs: one by the PS pump
https://www.dropbox.com/s/1yilm1p6lg...00701.jpg?dl=0
And the other one by cyl #7, close to the fuel rail:
https://www.dropbox.com/s/ur7rlwp2ll...00702.jpg?dl=0
4- Loose ground hunting: I found the fans to be hard wired to the ignition switch, both of them. Removed the relays to make them stop. Could this affect something else? Are fans controlled by a thermoswitch or by the ECU? All grounds behind the engine seem fine, and there is one from the manifold to the firewall. I kept looking and found this:
https://www.dropbox.com/s/3mbrkpymu1...00700.jpg?dl=0
Thats the negative battery cable, grounding the body close to the P/S pump. I was excited about this finding. Took me quite a while to untangle the wires so I could fasten this to the body, had to remove the battery, battery tray, airbox, intake resonator, etc. In this area I also found the P/S vaccum lines disconected.
I put everything back together, grounding point throughly scraped with a file and lubricated for rust protection and then tightly fastened with a clean bolt. I was anxious....
Started the car and got the very same sick missfire.
When the RPMs get very low, the intake starts backfiring and eventually dies if the throttle is not opened further. This beast sounds lean.... but the spark plugs get dark....
The 12V mod is a good idea. I need to hook up a fuel pressure gauge and get real info. I wanted to spray the intake with carb cleaner to see if it would clear up by adding fuel, but I didn`t have a helper to keep the engine running while I sprayed the intake.
I am tired, its almost 1 am. Keep the good ideas coming, I am far from defeated.... yet.
Tomorrow: fuel pressure...
Thank you all!
- Angelo
99 GS400