Hi guys. In desperate need of advice and help. I posted this as well in Club NA-T but It never hurts to get help from all sides if at all possible. Hope you guys can help me. I'm stumped on this one. The car is an sc300 na-t. The problem is as follows: When I start the car the first time, it will idle smoothly and rev normally but after about 10 minutes it will start to idle rough like it is not firing on all cylinders and rev roughly as well. Driveability is poor at this point. I noticed though that even when it was still revving normally initially, the power was not all there. Here are the things I have changed and checked. New plugs (Denso IK20's), cap and rotor, wires, coil, igniter. Initially, I thought it might be just be the igniter because my tach isn't working properly now. It will only rev til about 2k when the motor is really at about 5-6k. Mechanic said that usually a bad igniter can cause these problems with the tach. Speedometer is also jumping around but barely moving. I don't know if the tach and speedo are related to the engine problems but I just put it out there because I didn't have these problems before. My mechanic is now suggesting that I try different plugs but i'd like to get your opinions on what you might think is causing these problems. It has gotten to the point that I'm thinking of looking at other things now. Might my fuel pressure be too high and can this cause the problem? Could dirty injectors be a cause. the car has been unused for sometime now and I am only now getting back to putting it in shape again. It was okay when I parked it for storage for about a year. The ignition wires I put in are new but have been in my storage for about 3 years. Could they have gone bad? Might the rotor have been installed incorrectly to cause this kind of problem when the car is at normal operating temp? I was all gungho to get this car back on the road and now its just a source of frustration. Particularly frustrating since the car has less than 27k miles on the original motor. Really could use your help here. Thanks

 

ok, what year is the car?
what turbo setup?
what injectors?
what are you using for fuel correction?
do you have any CEL codes?
do you have any gauges?
do you have a wideband?

you can't just post a loaded thread like this and say "the car is a sc300 na-t" like the na-t was a factory option or something. you have to tell us everything about the car.

also, feel free to tell us about this mechanic. he thinks that spark plugs --while having extensive mods done to a car (like you have)-- will cause a car to run so terribly that you can barely drive it, especially when it already has new spark plugs?

it could be a bad igniter, but they RARELY go out on these things, and the gauge clusters (tacho, speedo, needles, lights inside, etc.) are infamous for a premature malfunction and/or death.

i'm going to give you the benefit of the doubt here and assume that you all drained the 3 year old gasoline out of the tank before trying to troubleshoot this thing further...

^ this is the only indicative part of your post. this leads me in the direction of this being a fuel problem. my reasoning:

when you first start your car, the ECU richens the fuel mixture up considerably (5-20%, maybe more depending on how cold it is outside). so while your engine is running rich, it's running smoothly. after the engine warms up to "operating temp," the ecu leans the mixture out to where it's supposed to be. this is called cold start enrichment. all stock ECUs do this.

if you drained the gas (again, i'm assuming you did) then just fill us in with some more useful information and we can try to get it figured out. if you didn't, tell your mechanic to take up a new profession, then head to the gas station.

 

Thanks for the reply. My bad on the inadequate info:

Car is a 1993 OBD1
It uses a Toyomoto setup with a Greddy TD06-20G turbo, 2.5mm HG
Stock injectors with 2 additional 550cc injectors
Sard FPR installed
Greddy Profec EBC
Stock ECU
Haltech AIC for the 550's at boost
No CEL codes whatsoever
No fuel correction due to stock injectors
Only EGT, Boost gauge, and useless Narrowband
Just bought a wideband but still has to be installed
The turbo was completely rebuilt due to worn seals. This was the initial reason why the unit was stored for some time All replaceable parts were changed except housing and shaft/impeller (upon rebuild and install, the unit was leaking a bit of oil until the seals completely seated.) I replaced the plugs to new Denso IK20's at that point.

Yes, Gas tank was thoroughly cleaned (as in brought down) before even working on the engine, fuel drained and new walbro 255lph fuel pump installed and new fuel filter down the line.

The car doesn't sound like it is lean when it starts to act up. It sounds like it's only working on 5 cylinders and there is a smell of unburnt fuel at the exhaust but it is not smoking excessively at idle or low rpms. The exhaust tips seem wet but I don't know if that's just moisture or gas.

As mentioned, the igniter, coil, cap, rotor, wires, and plugs have been replaced. The only thing I'm considering now is that maybe one or two injectors are dirty and are not firing well. Maybe I should take them out to have them cleaned. Is this adviseable?

Please let me know if I may be missing any more info. Thank you!!!

 

Nice, haven't seen the additional 2 injector setup in a long time.
sounds like an electrical issue. Did this cluster work previously?
I would definitely inspect the rotor, make sure the edge is not worn at all and smooth. If you have anythin but a toyota rotor and cap rip it out and get the oem stuff, I had an aftermarket rotor and cap fail on me pretty fast once, i was definately running on 2-4 cylinders when it happened.
was the distributor removed when all the maintenance was done? if so check the base timing by jumping the diagnostic terminal, and make sure it is close to spec i think 10 degrees.
you can also manually turn the motor over to TDC, remove the cap on the distributor and verify that the rotor is pointing directly at the cam sensor inside. If it is not, then it was not reinserted properly, and it should be corrected.

If all of that checks out, I would try and swap the ecu. there was another similar thread on here where the car was running badly (missing) and the car would not throw any CEL's. Turns out the ecu was bad, cause generally if you are misfiring you should be tripping some code of wether it is too rich, too lean, or random misfire code.
So I would do a check and put the key in the ignition, turn it 1 click (engine off), and see if your cel light even comes on. If it doesn't it could be a sign of a faulty ecu.

the tach acting wierd does not automatically mean the ignitor is bad, although it could be. when the coil fires off the pulse it generates is used to generate a return signal IGF in the ignitor and is also used to drive the tachometer (internally in the ignitor). If there is a no spark condition, the ignitor will not see the pulse and will know there was a misfire, so it will not send IGF or Tach signal, which in thoery cold cause the tach to act up, but the kicker is when the ecu does not get a return IGF from the ignitor it will shut off the injectors, and since your motor is still running, misifiring, and dumping fuel, all your spark events are still occurring, or your ecu simply does not care cause its fried. My first guesses would be they are firing at the wrong time, or you have a bad ecu.

In fact the thread with the bad ecu would also only occur when the car got warmed up, turned out the area next to the ecu got very wet from a bad weather sealing. something about it heating up would cause it to go crazy, but would work when cold. its worth a quick inspection of the ecu.
https://www.clublexus.com/forums/per...-92-sc400.html

 

Thanks Ali, I'll check on the items you pointed out. One question about the timing....if the rotor was incorrectly installed, wouldn't the car idle poorly as soon as it is started and not just go bad after 10 minutes? The cap and rotor are original from the Lexus dealership. The rotor tip is smooth. The one I replaced previously had parts of the flat edge worn out or ground down. The old distributor cap also had wear marks on the terminals inside the cap. Yes the mechanic did open up my distributor cap when he installed the new rotor and the cap. I didn't know that it could be installed incorrectly. I will definitely check the timing to see if it is at -10 btdc while jumping the E1 and TE1 ports. The Check engine light goes on when I turn the ignition and shuts off when the engine has started. I have also checked to see if there were any stored codes and there were none. I'm hoping it's not the ecu. Hopefully, it is just something simple that we may have overlooked. wish me luck and thanks for the valuable advice.

 

no problem, yes cap and rotor would show up when cold so its probably alright. There is only one way the rotor can screw on, i dont think you can install it backwards, there is a notch. Same with the cap if you have the OEM cap. If you swapped out to a 4runner cap to better clear the turbo the wire #'s are different, but you said you have the oem one still, so not an issue.
The timing wouldn't go out from replacing the rotor and cap, only if the whole distributor was moved, like the base or pulled out. If just the cap and rotor then timing should be fine as well.

have you tried resetting the ecu, that seems to be the problem with alot of people running on the stock ecu lately. what it learnt 3 years ago may not be good anymore, may need to clear out the settings. when you first start up the car you are in open loop with no adjustments, and once it warms up its using whatever adjustments were stored previously. anytime you make a modification or tune up on the stock ecu I always give it a full reset. If you had the wideband installed it may be easier to diagnose. sometimes the stock ecu can freak out and want to idle as lean as 16:1. after a reset everything would go back to normal. i would do this every other week or so to keep everything running consistent.

 

Mine was doin the same thing. I put a jumper wire on the diagnostic port and bypassed the fuel pump ecu and its running great now

 

Very odd, but my car is doing the same thing it sounds like, but mine is a GTE motor.

I checked my timing with a timing light gun and it's like 20 Deg BTDC!! Wow...it's in total limp mode at the moment. Your's probably is too.

I'd definitely bypass that fuel ecu as stated above, and if that's not it. Check the timing for sure.

 

Thanks for the input guys. Well, I've already bypassed the fuel pump ecu by doing the 12 volt conversion that skips the 9 volt default unless that doesn't do the same thing. I'll go check the timing next and see if my problem lies there. I really appreciate the help guys.

 

Yeah mine started doing it again today. Im going to get a new ecu tomorrow and ill try replacing it instead. If anybody has any other ideas i sure would appreciate it lol. Ill let ya know how it does after the replacement also

 

Ok well i put the new ecu in today. Aftwr i replaced it i took the fuse out of the fusable link i bypassed it with and it still wont run. Same thing it drives great then all of the sudden cel light and it died. Ive searched for a while and only have one more option left i believe. I noticed that the valve cover gasket was leaking a little bit. Is it plausible thatit is dripping onto the plugs? I have replaced the plugs,wires,alternator,igniter,fuel pump ecu, fuel pump and checked every fuse i know lol. Does ANYBODY Have any ideas?

 

I doubt its leaking enough to cause the motor to completely shut off. maybe run roughly or miss some. take the cover off and look at the front plugs, and you can also reach the rear most plug without taking off the manifold. check the front or back depending on where you think its leaking from. The OP is not getting a check engine light, you need to pull your code if you are getting a CEL and tell us what it is. what is your setup and symptoms? maybe start a seperate thread.

 

Is it possible that the rough idle might be caused by a misfiring or clogged injector? This was suggested to me and I think i'll investigate the possibility.

 

sounds like you are having fun.... If an injector was stuck computer should pick it up on a CEL code but it is possible. If stuck you should smell the fuel. Maybe we are not looking in the right direction for this car, it may not be intake, fuel or electrical. I am suggesting this because i had the same problem and i found out something very interesting, the exhaust is clogged in mine. It runs fine at start up for a few mins, then bogs down and when i give it throttle it limps. also I know it sounds crazy but the exhaust being clogged is still causing computer to run normal, when i have so much back pressure that it is bogging down. it is still sparking and igniting in the combustion chamber, just enoguh to make it run like crap though and just enough to not throw a code. another old more unlikely question, were valve springs replaced? sagging springs will cause horrible run issues and not throw a code. too much we are relying on a diagnostic tool when there are other old problems that happen. not as common, but do happen.

 

Alright, I think we found the problem or at least part of the problem. Injector number 3 is either clogged or malfunctioning. We did this test by removing the connector on each injector one at a time and all the others would affect the idling character of the engine except for number 3 which remained unchanged. I will now have the injectors all removed and cleaned just to make sure they are firing at optimal levels. As a precautionary measure, we will also do a compression test on each cylinder to determine if there are any problems with the rings. I am hoping nothing is wrong because this vehicle has not really been abused and has always been monitored for any lean fuel conditions. If anything we would always err on the side of being a bit too rich. Add to this the fact that this vehicle only has 26k miles and I'm hoping to find no surprises.

Can you guys please tell me what the ideal compression numbers should be for the 2jz-ge motor so I can be guided accordingly? Thanks! I was also deliberating on installing the 460cc injectors that are all clean and ready for install since my LS400 MAF and SAFC2 unit are waiting in the wings but my gut feel is to first find out if the original injectors are indeed the only problem before I add a new variable to the equation. Installing the new injectors would eliminate the need to get the old injectors removed, cleaned, reinstalled again only to have them removed shortly afterwards. It's just that I want to be sure everything on the baseline is working fine first so I have some peace of mind but if you guys think this is an unnecessary step, i'd like to hear from you. Thanks a bunch! I'll keep you posted on the progress.