Timing light showing wrong

[hammerhead]

When I connect the timing light, the RPM meter on the light shows double the rpm its really running. Any ideas? Once when we were playing around with some wiring around the cps, it showed correctly for a while, but now its bad again.. Also got slight miss in engine. Not a steady one-cylinder miss, but a random misfire. Also on some cylinders it just lights up random, as if there is weak spark or something.

thanks in advance, my car has spent the past year and a half in and out of the garage, and I had some things that my mechanic and I just couldn't figure out. I plan to do a write up soon hopefully, once i get everything cleared up.

 

[Supra]

When I connect the timing light, the RPM meter on the light shows double the rpm its really running. Any ideas? Once when we were playing around with some wiring around the cps, it showed correctly for a while, but now its bad again.. Also got slight miss in engine. Not a steady one-cylinder miss, but a random misfire. Also on some cylinders it just lights up random, as if there is weak spark or something.

thanks in advance, my car has spent the past year and a half in and out of the garage, and I had some things that my mechanic and I just couldn't figure out. I plan to do a write up soon hopefully, once i get everything cleared up.

The Supra is a wasted spark system using 3 coils on 6 cylinders. Each coil fires twice per one engine rotation. Your timing light SHOULD read double your tach because it's picking up cylinder #1 when #1 fires, then it picks up cylinder #1 a second time when #6 fires (same coil fires twice, two plug wires from the same coil, make sense?).

Edit: If your tach read correctly, it's because one of the two cylinders wasn't firing. Bad wire or plug on #1 or #6. FYI, it's easier to clamp plug wire #6 since #1 and #6 are paired.

 

[hammerhead]

hmm.. that makes sense. Here's the problem, I've been meaning to share it a long time, but my mechanic and I have been too busy trying to figure it out ourself.

You say bad wire or plug. but if I swap the plugs and wires, it stays on the same cylinder. Then you say maybe bad coil.. I swapped those too, and the coil is good. Any ideas left?

 

[hammerhead]

BTW, Rich87 are those Borbet wheels? That's a replica of my car.. except for the CF hood on my car.

 

[hammerhead]

in addition, the voltage and resistance on the igniter and pickup coil wires all tested to spec. I'm leaning on the CPS being the only thing that could possibly be off.. even if the Vantage system tested it ok..

(please note, my opinions only count so much, only things i know about mechanics is what i have learned reading SM and working on my car)

 

[cjsupra90]

I'd suspect the Ignitor before the CPS if it is ignition related. The CPS has nothing to do with cylinder identification except for CYL's #1 and #6 referance so the ECU knows where the motor is at based on the G1 and G2 pickup signals and the count on the NE pickup signal. The ECU and the ignitor work together to determine which cylinder to fire.

Also, remember it could be fuel related. A missfire is not just and ignition thing.

About your timing light, being that it has a built in RPM meter, it should have a setting that can be changed between 4 cycle and 2cycle. On a waste spark system like used on the 7M-GTE, the setting should be changed to 2cycle and then it will read correctly

 

[hammerhead]

I'd suspect the Ignitor before the CPS if it is ignition related.

my mechanic used his vantage system to check the voltage patterns on the igniter, and it checked out fine, is it possible the thing could be bad and still give out correct voltage patterns?

Also, remember it could be fuel related. A missfire is not just and ignition thing.

My fuel pressure tested to be 32 psi at idle, and jumps to around 60psi if I give it WOT.

About your timing light, being that it has a built in RPM meter, it should have a setting that can be changed between 4 cycle and 2cycle. On a waste spark system like used on the 7M-GTE, the setting should be changed to 2cycle and then it will read correctly

Thanks, I'll check it out next time i go to the shop.

 

[hammerhead]

Ok, so it's a waste spark system, so what would cause it to show the correct rpm on the timing light for a few seconds, when we were fiddling around with the CPS?

 

[rumptis]

The reason its not showing the correct RPM is that we have 3 coil packs and each coil feeds 2 spark plugs...so each coil pack has to fire twice per revolution of the engine. This means that each spark plug fires twice for each revolution and you gun thinks that each time it fire's is 1 revolution which is why its reading twice that amount. Because each plug fires twice per revolution.

So there is nothing wrong with your gun or your car you just need to divide the RPM in half and that is the true RPM.

I hope that makes sense.

 

[Supra]

Ok, so it's a waste spark system, so what would cause it to show the correct rpm on the timing light for a few seconds, when we were fiddling around with the CPS?

I get what you're saying. Sometimes it reads double (correct) and sometimes it reads actual (incorrect). A one cylinder problem is going to be "ignitor -> coil-> wire -> plug -> cylinder".

The wires at the top of the CPS are known to get brittle and cause run problems. I don't know about single cylinder misfire, but "engine cranks but no spark" is commonly CPS wire related. As far as I know, the CPS does not affect spark on a per coil or per cylinder basis and therefore should not cause your problem. It does affect spark on a global scale, such as base timing.

Just to get back to the basics of 7MGTE misfiring...

Do not use Bosch platnums - they cause elec. interferance and misfire. I recommend NGK copper plugs (BCPR6ES). Gap ~.030". Adjust to your specifics.

The wires are usually the next problem. I recommend using only stock. MSD have crap fitment to stock coils.

The ignitor is another 'typical' problem area.

If the problem isn't moving with the spark plug or wire but still appears to be a single cylinder misfire, I have to ask the obvious. Is the engine misfiring? If a cylinder is going dead and your light is showing this, is the engine actually stumbling? Is your timing light "smart" enough to figure out # of cylinders and automatically switching? Or is that a manual setting?

If the engine is stumbling, I'd check the cylinder. Make sure compression is good. Swap a fuel injector.

*********************************

To the guy that asked about my rims:
Supra has Kosie Senica 17" rims with Kumho tires.
Mini has Mini Light 10" rims with Yokohama A007's :biglaugh:

 

[hammerhead]

I think if the circuit is broken with one of the cylinders for a coil, the spark is cut it half... making it show actual rpm instead of double.

I read elsewhere on this forum about someone having a problem with the timing light flashing random, or not at all.. I have this same thing too sometimes.. If this happens, when you take off the plug wire and let it spark across instead of making a solid connection, then the timing light flashes the way it should..

i hope that was explained properly... I mention that just so that someone interested in studying the supra's ignition system can try and make sense of it.

 

[hammerhead]

I'm gonna let my mechanic read that, he was getting intrigued by the ignition system.. I'll see what he says...

 

[cjsupra90]

Sometimes on waste spark systems, you will only pick up one of the two firing cycles, do to the substantially lower voltage used during the exhaust firing cycle. One thing that is a big misconception about ignition coils being used in an inductive type ign. system is that the coil will only put out the voltage that is needed to jump the gap at the plug regardless of how much the coil can put out. example is lets say you have a 50,000 volt coil, that doesn't mean that you are going to get the full 50,000 volts. If only say 25,000 volts is needed, then thats all that the 50,000volt coil is going to put out.

Now a waste spark type coil that has two wire outputs and fires two seperate plugs, outputs the required voltage requiered two jump the gap of the two plugs in there given condition. The cylinder thats in compression will requier a lot more voltage then the one that is in exhaust. Example to explains this a little better is that cylinder in compression may requier 25,000volts where as the cylinder in exhaust may only requier 5,000volts so the coil will attemp to output roughly 30,000volts. The voltage output will vary with engine load which will raise or decress cylinder pressure and therefor the needed voltage to jump the gaps.

Now being that very little voltage is needed on the exhaust firing cycle especially while idling (due to very low volumetric effiency (therefor very low cylinder pressures)) if the plug wires being used have a very high supression strength and a timing light does not have a very sensitive inductive clamp and therefor can not pick up the very low EMF's (electro magnetic feilds) then the light might not pick up the exhaust firing cycle on a given cylinder.

 

[IHI-RHC7]

I miss your posts, Chris
I have to side with rich on this one.
"cyl 5 misses, we swapped plugs with cyl2 and 5 still misses, swapped wires, etc."
If cyl 5 consistantly misses, then cyl 5 probably has a problem, be it fuel, compression, contamination, etc...

My fuel pressure tested to be 32 psi at idle, and jumps to around 60psi if I give it WOT.

If your regulator is working correctly, then the fuel pressure should jump roughly 15 psi in neutral when opening the throttle. if yours is jumping 28 psi, that is alarming, unless you are actually building boost when it reaches 60 psi. If you aren't building boost, it seems to me that you have a restriction in your fuel return line, causing fuel pressure to rise at a rate greator than 1:1 as it should.
Bottom line is that you need to know the physical condition of the engine before you can say that it must be electrical. Also, I find that NGK wires fit as good as stock. I'm not sure about magnecore, though.
Hope this helps,
-Jake

 

[Supra]

Also, I find that NGK wires fit as good as stock. I'm not sure about magnecore, though.
Hope this helps,
-Jake

I've also heard lots of good things about NGK wires, but never used them myself.

I got the MSD wire set for free. The clips that attach them to the coil were horrible. Literally would fall off. :3d_frown: