'98 GS400 Cranks, no start
06-04-16, 07:54 AM
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'98 GS400 Cranks, no start
Hey guys,
I recently picked up a '98 GS400. It will crank but not fire. So far here's what I've tried:
1)The keyfob is broke so the remote locks won't work but the car will lock/unlock with the key in the door. The security light to the left side of the dash flashes until the key is in the ignition and then turns off. So I don't believe I'm battling an immobilizer problem.
2) The car is getting fuel and fuel pressure. It was sitting for years so I drained the tank and added a couple gallons of fresh fuel.
3) The ignition coils have 12v at two of the lugs at the coil connector and almost 6v positive at one lug with just the key on. From the Mitchell/AllData wiring diagrams I believe that two of the lugs are constant ground while the inner two coming from the ECM should be "switched" +12v and a pulsed/triggered signal. 6V at key on at one of the lugs from the ECM sounds weird to me. Tested spark output with a spark tester in the coil boot to ground. No spark while cranking.
4) I have not tested if there is pulse at the injector with a noid light, but I did use a multimeter and was getting fluctuating voltage while cranking. Telling me my DVOM was responding slowly to the voltage pulses but trying to play catch up.
5) Using an Autotap Xray scanner there are no stored or pending OBD codes, MIL is off. While viewing engine RPM data it does read RPM while cranking, usually around 135-140rpm.
6) The car does have uneven cranking like the starter is powering through varying levels of compression resistance. Possible head gasket problem or valves problem. I'm currently doing a compression test of each cylinder to get a clearer picture. However, I've never known a head gasket on a V engine to cause a complete no start condition. Even if there was zero compression in a couple of cylinders it would still fire, buck, kick, run rough or vibrate to all hell.
7) All underhood fuses and relays have 12v.
Obviously my problem is the lack of spark. (I'll cross that compression/head gasket when I get there) I just need to narrow down the source. Either the ECM isn't getting it's voltage or a bad ground somewhere. Possible bad ECM. Or could I be completely on the wrong track and this is how the immobilizer works, by allowing vehicle to crank but kills spark?
Anyone run into a similar problem or is there an obvious known problem and fix?
Appreciate your input. Cheers.
I recently picked up a '98 GS400. It will crank but not fire. So far here's what I've tried:
1)The keyfob is broke so the remote locks won't work but the car will lock/unlock with the key in the door. The security light to the left side of the dash flashes until the key is in the ignition and then turns off. So I don't believe I'm battling an immobilizer problem.
2) The car is getting fuel and fuel pressure. It was sitting for years so I drained the tank and added a couple gallons of fresh fuel.
3) The ignition coils have 12v at two of the lugs at the coil connector and almost 6v positive at one lug with just the key on. From the Mitchell/AllData wiring diagrams I believe that two of the lugs are constant ground while the inner two coming from the ECM should be "switched" +12v and a pulsed/triggered signal. 6V at key on at one of the lugs from the ECM sounds weird to me. Tested spark output with a spark tester in the coil boot to ground. No spark while cranking.
4) I have not tested if there is pulse at the injector with a noid light, but I did use a multimeter and was getting fluctuating voltage while cranking. Telling me my DVOM was responding slowly to the voltage pulses but trying to play catch up.
5) Using an Autotap Xray scanner there are no stored or pending OBD codes, MIL is off. While viewing engine RPM data it does read RPM while cranking, usually around 135-140rpm.
6) The car does have uneven cranking like the starter is powering through varying levels of compression resistance. Possible head gasket problem or valves problem. I'm currently doing a compression test of each cylinder to get a clearer picture. However, I've never known a head gasket on a V engine to cause a complete no start condition. Even if there was zero compression in a couple of cylinders it would still fire, buck, kick, run rough or vibrate to all hell.
7) All underhood fuses and relays have 12v.
Obviously my problem is the lack of spark. (I'll cross that compression/head gasket when I get there) I just need to narrow down the source. Either the ECM isn't getting it's voltage or a bad ground somewhere. Possible bad ECM. Or could I be completely on the wrong track and this is how the immobilizer works, by allowing vehicle to crank but kills spark?
Anyone run into a similar problem or is there an obvious known problem and fix?
Appreciate your input. Cheers.
Last edited by Mykk; 06-04-16 at 07:58 AM.
06-04-16, 08:41 AM
#2
Hey there, welcome to Club Lexus 
As for your issue, personally, I'd start by removing the intake at the elbow, soaking a rag in fuel and hold it up to the opening (tightly as to not have it suck in while you crank) this will at least completely rule out that its not a fuel issue. I've worked on a vehicle before that had fuel pressure, but still wouldnt start because it wasnt being sent while it was cranking.
As for spark, could also be your crank sensor. Could also possibly be your starter as well. It could be so worn that it draws so many amps while cranking the engine that there’s not enough juice to send what it needs to the pump or coils etc. Easy check, just use a multi-meter and check for voltage drop while cranking. Worst case scenario, could be a BCM issue.
As for your scanner, I assume you didnt fork up a butt load on one? Not all scanners are created equal. I'm yet to find a inexpensive scanner that will give you ALL the codes (including dealer codes) The aforementioned vehicle with the BCM issue wasnt giving me the codes with an autozone scanner, but when I hooked up the Snap-on... BAM codes all the way down to minor issues that would never show up on a entry level scanner.
Anyways, those are a few things you can add to the list. Good luck and keep us posted
As for your issue, personally, I'd start by removing the intake at the elbow, soaking a rag in fuel and hold it up to the opening (tightly as to not have it suck in while you crank) this will at least completely rule out that its not a fuel issue. I've worked on a vehicle before that had fuel pressure, but still wouldnt start because it wasnt being sent while it was cranking.
As for spark, could also be your crank sensor. Could also possibly be your starter as well. It could be so worn that it draws so many amps while cranking the engine that there’s not enough juice to send what it needs to the pump or coils etc. Easy check, just use a multi-meter and check for voltage drop while cranking. Worst case scenario, could be a BCM issue.
As for your scanner, I assume you didnt fork up a butt load on one? Not all scanners are created equal. I'm yet to find a inexpensive scanner that will give you ALL the codes (including dealer codes) The aforementioned vehicle with the BCM issue wasnt giving me the codes with an autozone scanner, but when I hooked up the Snap-on... BAM codes all the way down to minor issues that would never show up on a entry level scanner.
Anyways, those are a few things you can add to the list. Good luck and keep us posted
06-15-16, 07:42 AM
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Thanks for the feedback.
I did get the car to fire, it wouldn't want to start due to low/lack of compression. After a compression check 5 out of 8 cylinders had no or very very low compression, the other 3 were in the low end of the spectrum. I deemed this car just a little too hurt and far gone then ended up selling it as a parts car.
After searching the forums and seeing the amount of problems with starting/ running/ stalling issues I'm inclined to say these vehicles are extremely sensitive to compression.
Thanks again for your input
I did get the car to fire, it wouldn't want to start due to low/lack of compression. After a compression check 5 out of 8 cylinders had no or very very low compression, the other 3 were in the low end of the spectrum. I deemed this car just a little too hurt and far gone then ended up selling it as a parts car.
After searching the forums and seeing the amount of problems with starting/ running/ stalling issues I'm inclined to say these vehicles are extremely sensitive to compression.
Thanks again for your input
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