2of6 cylinders spark after 800rpm (SOLVED)

[beemerguy]

Car is a 2002 Lexus GS300 with150,000 miles. Engine was bad when we bought it so we replaced the engine with the same one from a 2001 GS300. The problem is that 2 o f 6 ingnitors fire ONLY after 800 RPMs. Wiring from engine computer to distributor and coil is ok. We’ve swapped the coils and I get the same results. alast thing we checked is the pins at the engine computer. We put a voltmeter to see when the engine computer sends pulses to the ignitors and it seemed like it was sending the signal too late so we got a new computer. Even with the new computer we still have the same problem. We are completely baffled and the only thing we can think of is change the entire engine wiring harness. Any tips?

Topic

[dreamer2355]

Welcome to the forums!

How are you checking for spark and what type of ignition system do you have?

Did you mechanically check the timing?

[beemerguy]

Thanks for the welcome!! We are checking the spark by manually removing it from the engine while the engine is on. When we take the plug out we can clearly see it firing only after 800rpm. The gs300 has 3 wires that run from the engine computer to the 6 coils. We checked the pins on the engine computer using a voltmeter and noticed that 2 of three wires are constantly sending pulse signals which command the plugs to fire. The third wire only send the pulse signals when the rpms have reached over 800. Before 800rpm there’s no signal in that particular wire. We didin’t check the timing after the job was done. I’m definetly gonna look into that suggestion. Thanks a milion, that was a good tip

[EricTheCarGuy]

I believe that engine uses a waste spark system meaning that one coil will fire 2 plugs and if I’m not mistaken 2 and 6 are sister cylinders on that engine meaning that they both use the same coil. I would recommend swapping coils with another cylinder and if the problem follows the 2/6 coil then replace the coil.

[beemerguy]

Hey Eric, Thanks for the tip. You’re right 2 plugs fire on one coil. We tried swapping the coils but it won’t fire on the same two cylinders. Next we tried jumping the signal from the ECM to that particular coil and it’s the same result. Then we tested the 3 ignitor data pins at the ECM which send the ignition signals to the 3 coils. Pin 1 and 2 show pulses being generated at all rpms. Pin 3 doesn’t show any pulses until the engine reaches 800rpms+. We replaced the ecm with a new one and its the same result. Next we rechecked the timing and replaced the Maf but same results.

Now we are planning to buy a new engine wiring harness and hope for the best. At this point we are baffled as to why the 3rd ignitor only fires after 800rpm.

I’ll keep you guys posted and any other tips pleaseee let me know.

Thanks!!

[Matt]

That’s a wierd one. I really don’t have much to offer without seeing the car in person, but if you bypassed the wiring to the igniter and it didn’t change, I can’t see how replacing the harness is going to help. I’ll try and find a wiring diagram and see if I can offer anything better. You may have to bite the bullet and take it to a shop however, as you have done everything I can think of from the other end of the interwebs at this point. I’ll try and poke around though.

Also, did you hear the engine run before you bought it? Did it present this problem as soon as it was swapped in? Did you use the harness from your car? And do you know if the engine did this before you bought it with the engine being bad?

[EricTheCarGuy]

Be sure that you’re doing your testing correctly because you seem to be talking about a lot of work replacing a harness not to mention the stuff you’ve already replaced. I think you need to find yourself a proper wiring diagram with the pin outs for the ignition system and take your readings directly at the PCM, if you still have the same readings there I would suspect a PCM issue but if not it’s in the wiring somewhere and if you have a wiring diagram you’ll know where the connectors and wires that you need to check are located. Electrical diagnosis can be tedious but it’s well worth the effort so take some time and research the circuit and do some testing before you just start throwing parts at it. The ideal would be to get your hands on a lab scope so that you can look at the waveforms for the faulty signals but I understand that would be a difficult thing to do so for now arm yourself with information and a DVOM and see what you can find.

[beemerguy]

– Yes we heard the engine run before we bought it. It was out of a 2001 crashed car. Don’t know if this engine had this problem before buying but it did run a little rough. The problem was present when

[dreamer2355]

Quoted From beemerguy:

– Yes we heard the engine run before we bought it. It was out of a 2001 crashed car. Don’t know if this engine had this problem before buying but it did run a little rough. The problem was present when we installed it. We used the original 20002 harness from my car.
– Engine computer has been replaced and programmed to the car (didn’t solve the problem

The reason I want to replace the harness is because the original 2002 harness had some broken connectors and were mended. I’m not sure if the harness has internal issues somewhere causing a delayed ignition signal to the ECM. Can a bad wire cause the ECM to get a late signal on ignitor 3??

Just got my hands on the GS300 wiring manual. I’ll start researching on how to retrace the individual ignitor 1-2 and 3 signals.

Thanks for all the tips!!

Any bad wires to the ECM will cause an array of issues. You also have the option of doing some voltage drop testing to rule out any wiring issues.

[EricTheCarGuy]

It won’t cause a delay but it will cause a voltage drop if there is increased resistance somewhere in the circuit, use the wiring diagram to find what wires are involved in the effected circuit and look for increased resistance in those wires. I might start at the ECU to see if it’s putting out the signal, if it is then follow it to the coil to find the cause.

[beemerguy]

Finally found the problem. Turned out that the Crank Sprocket had hairline cracks on it and caused a bad signal. Crank sprocket is metal and since the hairline cracks were extremely thin, it would cause misreads at low rpms but the electrical signal worked perfect after 800+ rpms. Replaced the crank sprocket and problem solved. Thanks a million for all your tips!!!!!!!!! Hope this helps someone in the future

[Trcustoms719]

Interesting..
Thanks for posing the fix.
Great job.

[Matt]

Nice work bud. Make sure you turn the traffic light ‘green’ so others with similar problems can search the database and find your fix.

[college man]

Thanks for the update and the fixC8-)

[dreamer2355]

Thanks alot for posting the fix. This one had me stumped. Visual inspections are key!

[EricTheCarGuy]

Yea it’s great you found the problem and were able to fix it, that’s a pretty strange issue and would be difficult to find so well done you. Thanks for posting the fix and for using the ETCG forum.

[Author]

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