When you click on links to various merchants on this site and make a purchase, this can result in this site earning a commission. Affiliate programs and affiliations include, but are not limited to, the eBay Partner Network.
Hi all!
I just inherited an 03 SC430 with a few issues that have me stumped. I apologize if this is covered somewhere else, I searched and didn't find anything similar to my issues. Here goes!
Vehicle cranks and starts normally when cold. After driving ~20 minutes and parking for a half hour it has a really hard time starting. It can take 15 minutes before it finally starts. Once in awhile during this issue it will stumble for a few seconds before dying off. I was told that Lexus diagnosed it as needing a fuel pump. I am reluctant to change the pump due to the fact that it starts perfectly fine when cold, and has no bogging or lack of power as long as it's running.
My first initial thought was crank sensor, as I've seen them fail intermittently on hot soak. So I connected my scanner and monitored the Engine RPM PID during one of these no start occurrences. I had normal cranking RPM reading, roughly 200 RPM. So I don't believe that's my problem.
Next thought was the key, but the security light turns off every time the key is inserted. And during these no/hard start events it's always off.
I pulled the fuel pump relay to see if maybe it's sticking when hot, and it was almost too hot to hold. It's a 4 pin relay, 1&2 are control pins, 3 is constant and 4 is the switched pin. I have continuity on my control side, and continuity between pin 3&4 without power applied. When I apply power to 1&2, I lose continuity between 3 and 4. My shop manual says I'm supposed to only have continuity with voltage applied. Is this normal?
Then I went to move the car and forgot to insert the fuel pump relay. And it still started and ran. WTF?
I'm just stumped as to where to go from here, and would really appreciate any insight. Thanks
I think hot relay can be normal. I'm just throwing a dart in the dark here, but I'm thinking cam position sensor. Whatever the problem is, your #1 clue is: AOK cold, won't start hot, AOK after cool again. Something is not reading right when hot. Again, total spit balling here.
Hi all!
I just inherited an 03 SC430 with a few issues that have me stumped. I apologize if this is covered somewhere else, I searched and didn't find anything similar to my issues. Here goes!
Vehicle cranks and starts normally when cold. After driving ~20 minutes and parking for a half hour it has a really hard time starting. It can take 15 minutes before it finally starts. Once in awhile during this issue it will stumble for a few seconds before dying off. I was told that Lexus diagnosed it as needing a fuel pump. I am reluctant to change the pump due to the fact that it starts perfectly fine when cold, and has no bogging or lack of power as long as it's running.
My first initial thought was crank sensor, as I've seen them fail intermittently on hot soak. So I connected my scanner and monitored the Engine RPM PID during one of these no start occurrences. I had normal cranking RPM reading, roughly 200 RPM. So I don't believe that's my problem.
Next thought was the key, but the security light turns off every time the key is inserted. And during these no/hard start events it's always off.
I pulled the fuel pump relay to see if maybe it's sticking when hot, and it was almost too hot to hold. It's a 4 pin relay, 1&2 are control pins, 3 is constant and 4 is the switched pin. I have continuity on my control side, and continuity between pin 3&4 without power applied. When I apply power to 1&2, I lose continuity between 3 and 4. My shop manual says I'm supposed to only have continuity with voltage applied. Is this normal?
Then I went to move the car and forgot to insert the fuel pump relay. And it still started and ran. WTF?
I'm just stumped as to where to go from here, and would really appreciate any insight. Thanks
my 2000 Trans Am is a hard starter when hot...in my case it’s the fuel pump.
when cold, it starts right up.
when hot, I turn the key on for five seconds, turn it off then back on and it starts right away everytime.
when you turn the key on, the fuel pump primes and increases fuel pressure. The first time is not enough but the second time does the trick.
Thanks for the replies. I was leaning towards a sensor, but with Lexus's diag and your experience BGW I think I'll probably just end up putting a pump in it. I saw how easy it was when I was looking to see if there was any loose wiring to the pump. I was expecting to drop the tank initially since Lexus quoted almost $800 for the job. I'll have to get the cash together and swap it out and report back. Thanks again
Thanks for the replies. I was leaning towards a sensor, but with Lexus's diag and your experience BGW I think I'll probably just end up putting a pump in it. I saw how easy it was when I was looking to see if there was any loose wiring to the pump. I was expecting to drop the tank initially since Lexus quoted almost $800 for the job. I'll have to get the cash together and swap it out and report back. Thanks again
have you tried to cycle the key twice?
also, go to Autozone and rent a fuel pressure gauge with the proper fittings to test the fuel pump pressure.
Please Don’t swap the fuel pump without performing diagnostics first.
I have no idea what the resistor does, hopefully someone can shed some light on it. I rented the fuel pressure tester, and got some odd results.
If I cycle the key multiple times, I get 3-5psi. If I jump the fuel pump relay I get no increase in pressure. If I start the car I get ~47psi which is within specs (44-50psi). If I shut it off and watch the gauge it bleeds down to about 25psi which is also in spec (21psi min).
I also found the service history and come to find out that it's only had 5500 miles put on it in 4 years. I took a fuel sample after checking the pressure and it's very yellow. Could bad fuel cause a hard start only when hot?
And is it normal for these to start and run with no pump relay? I've looked at the schematics for the pump relay and it confuses me how it operates. It looks like the pump relay is not really even necessary.
Thanks again
I have no idea what the resistor does, hopefully someone can shed some light on it. I rented the fuel pressure tester, and got some odd results.
If I cycle the key multiple times, I get 3-5psi. If I jump the fuel pump relay I get no increase in pressure. If I start the car I get ~47psi which is within specs (44-50psi). If I shut it off and watch the gauge it bleeds down to about 25psi which is also in spec (21psi min).
I also found the service history and come to find out that it's only had 5500 miles put on it in 4 years. I took a fuel sample after checking the pressure and it's very yellow. Could bad fuel cause a hard start only when hot?
And is it normal for these to start and run with no pump relay? I've looked at the schematics for the pump relay and it confuses me how it operates. It looks like the pump relay is not really even necessary.
Thanks again
the fuel pump relay is confusing...I will look for my thread when I cleaned the fuel injectors...I show the fuel pump relay but it has a different name.
It looks like the relay might control the fuel pump speed
I am not the best at reading electrical things, but I think the pump normally runs slow because of the resistor. When you hit the gas hard, the relay closes and gives the pump full power. That is why the car runs with the relay out.
It looks like the relay might control the fuel pump speed
I am not the best at reading electrical things, but I think the pump normally runs slow because of the resistor. When you hit the gas hard, the relay closes and gives the pump full power. That is why the car runs with the relay out.
(I got this info from the attached document)
That makes a lot of sense actually. I couldn't find that document in any of the literature I have, so it was just confusing for me. Just to see what would happen I inserted the relay into the fuse block while it was running and I had the fuel pressure gauge connected. Every time I put it into the block I would see a 2-5psi change for a few seconds.
How hard is the tank to drop on these? I've got an EVAP code and I'm pretty sure it's the ORVR, gonna smoke it later today after the boss leaves. I figure while I've got it down I'll clean the tank of all that nasty old fuel. I was debating on just running the pump on a jump pack and letting it pump out the fuel pressure tester, but I don't think I want all that crap pushed through the system.
I Was looking into replacing my evap canister which is a MAJOR pain in the butt, but found out I just needed to replace the cracked hoses in the engine bay
That makes a lot of sense actually. I couldn't find that document in any of the literature I have, so it was just confusing for me. Just to see what would happen I inserted the relay into the fuse block while it was running and I had the fuel pressure gauge connected. Every time I put it into the block I would see a 2-5psi change for a few seconds. How hard is the tank to drop on these? I've got an EVAP code and I'm pretty sure it's the ORVR, gonna smoke it later today after the boss leaves. I figure while I've got it down I'll clean the tank of all that nasty old fuel. I was debating on just running the pump on a jump pack and letting it pump out the fuel pressure tester, but I don't think I want all that crap pushed through the system.
Why are you dropping the fuel tank?
You are jumping to major work again. Slow down and look for the easiest fixes first.
Darryl is correct...it is most likely a vacuum hose that is cracked, broken or just came off.
Tell us the code.
How many miles on your 2003 SC430?
If you have never changed the vacuum hoses, you need to inspect them very closely.
Also have some new vacuum lines ready to go if you start pulling them because some will crack and split.
I was going to drop it for sure if I found a leak, but was debating on dropping it anyway to clean out all the orange fuel. Either that or just run a hose off of the rail and use the pump to try to get it all out. I was just curious how involved it was. But I am definitely putting it on the lift and smoking it before I pull anything major.
As far as the PCV, I don't think it's ever been changed. Most of the vacuum lines look original. The code isn't set at the moment, it comes and goes. But when I scanned it while it was active it was a small EVAP leak, I think a p0456.
It's got just over 130k on it
Last edited by Erjar; 07-31-18 at 03:14 PM.
Reason: forgot information
That was the same code I had when I thought it was the Charcoal canister. I am glad the members on the board encouraged me to check for engine bay vacuum leaks. That was the solution.
I learned the hard way that by fixing one, the system would be pressurized and another crack would occur on a different hose. After the third time, I finally just changed out all the original hoses all at once and fixed the problem once and for all.
I am interested to see what your smoke test revels. According to this board, it could also be the gasket on your fuel cap.
07-29-18, 12:44 PM
2003 SC430 Intermittent hard start
