Detonation

[JD1964]

I think I'm experiencing detonation after a distributor cap change. Also changed wires but I can't see how this would cause it. After the cap change, it seemed to have noticeably better low end throttle response which would be indicative of advanced timing. But on WOT, it stumbles at about 4500.

I figured that the replacement cap would be exactly the same. But I guess manufacturing differences could require the timing be reset.

Got late and I couldn't keep making noise so I quit until another time. What do you think? Have you ever seen a cap change affect the initial timing enough to make a difference. ?

 

[JD1964]

Also, I wonder if it's possible that the new Moroso Ultra 40's resulted in advanced initial timing. Perhaps they are so much better than the old wires that the spark can jump farther. So, in the cap, the arc jumps from the rotor to the posts sooner, thereby resulting in an advanced initial timing.

I'll check it later and see but I just wanted to bounce these ideas around to see what others think.

 

[jozsefsz]

I really don't think a cap / rotor change would alter your base timing at all, but the only way to rule it out would be to check the timing. I don't believe the timing isn't really related to the cap & rotor position to one another, only a side-effect as the pickup in the distributor is aligned to them (when you rotate the distributor body, you're rotating the pickup in relation to cam position, and simultaneously slightly changing the rotor to cap position, the first part is what changes the base timing).

I'd suspect your high-end stumble is related to colder weather... I've always noticed spark blowout to increase when it gets cool out (denser air I'd suspect). My MSD coil (turbo not SC but running around 9psi) doesn't quite have the juice to jump the gap when it gets cold (with AFR looking good on the wideband) so I'll get high RPM stumbles / misses (and an occasional pop in the exhaust). Down-gapping the plugs is a good remedy unless you want to get fancy ($$) with a boost-a-spark or a high-end ignition system.

Better wires are definitely not going to cause a detonation problem or changes to timing. Unless those better wires are not routed well, which might cause some inductive cross-fire.

 

[JD1964]

Wierd thing is, it didn't do it initially in the first pull of the drive. I was doing trial and error setting my shift light. The first pull it did fine and went to the redline no problems. Then I drove around some more before adjusting the shift light setting. After that is when it started stumbling. I wonder if things were tolerable to the engine when the engine operating temp was cooler on the first pull. Then, on subsequent pulls the engine had heated up enough to make the issue happen. Thus, hotter engine more likely to have detonation. Hence, maybe need to reset timing after the wires, cap and rotor change.

Plugs are gapped at .032

 

[JD1964]

I really don't think a cap / rotor change would alter your base timing at all, but the only way to rule it out would be to check the timing. I don't believe the timing isn't really related to the cap & rotor position to one another, only a side-effect as the pickup in the distributor is aligned to them (when you rotate the distributor body, you're rotating the pickup in relation to cam position, and simultaneously slightly changing the rotor to cap position, the first part is what changes the base timing).

I'd suspect your high-end stumble is related to colder weather... I've always noticed spark blowout to increase when it gets cool out (denser air I'd suspect). My MSD coil (turbo not SC but running around 9psi) doesn't quite have the juice to jump the gap when it gets cold (with AFR looking good on the wideband) so I'll get high RPM stumbles / misses (and an occasional pop in the exhaust). Down-gapping the plugs is a good remedy unless you want to get fancy ($$) with a boost-a-spark or a high-end ignition system.

Better wires are definitely not going to cause a detonation problem or changes to timing. Unless those better wires are not routed well, which might cause some inductive cross-fire.

Spark blow out is on the suspect list too but this stumble is happening at about 2.5psi. And I'm gapped at .032 already. I'll start with ignition timing to rule it out first.

 

[jozsefsz]

.028's a good gap for a turbo, 0.032's probably good far a charger (though you're putting out some nice boost so you could go a little lower). Spark blowout is pretty unique, it feels like the car's cutting out entirely which then turns into a low-power stumble, and the exhaust starts to break up. It goes away as soon as you drop the throttle a bit. (Edit: if it's happening at 2.5psi it's not likely what's happening)

It certainly won't hurt to re-check your timing, though I still don't think the cap changes timing at all. If you haven't tossed your old parts you could put them on again to see if the problem goes away, that would definitely pinpoint the problem to the cap. (Did you swap the rotor along with the cap? A non-stock cap might be designed for a non-stock rotor to ensure the air gap remains the same. Also did you use dielectric grease on the new wire ends?)

It might be a bad cap, spark-related stumbles are because the spark isn't jumping the right gap for whatever reason (too much fuel or oil, too much compressed air, weak spark, jumping somewhere else, etc), typically not because it's doing it too well.

 

[JD1964]

I swapped the cap and rotor together. I did not use dielectric grease on the plug wire connections.

I see your point about the initial timing being triggered by the dist pickup rather than the rotor tip relation to the cap.

 

[JD1964]

I suppose stutter would be a better description of what is happening. No popping in the exhaust so ignition crossfire is not likely. I checked for arcing with the engine idling in the dark and saw none.

 

[jrichker]

Step 1.) Check the timing with a timing light. The auto parts store will loan or rent you one. Watch the spark advance change when you remove & reinsert the SPOUT.

Setting the timing:
Paint the mark on the harmonic balancer with paint -choose 10 degrees BTC or 14 degrees BTC or something else if you have NO2 or other power adder. I try to paint TDC red, 10 degrees BTC white and 14 degrees BTC blue.

10 degrees BTC is towards the drivers side marks.

Note: setting the timing beyond the 10 degree mark will give you a little more low speed acceleration. BUT you will need to run 93 octane to avoid pinging and engine damage. Pinging is very hard to hear at full throttle, so it could be present and you would not hear it.

Simplified diagram of what it looks like. Not all the marks are shown for ease of viewing.

ATC ' ' ' ' ' ' ' ' ' '!' ' ' ' ' ' ' ' ' ' BTC
---------------- > Direction of Rotation as viewed standing in front of the engine.

The ' is 2 degrees.
The ! is TDC
The ' is 10 degrees BTC
Set the timing 5 marks BTC. Or if you prefer, 5 marks towards the driver's side to get 10 degrees.

To get 14 degrees, set it 7 marks BTC. Or if you prefer, 7 marks towards the driver's side to get 14 degrees.

The paint marks you make are your friends if you do it correctly. They are much easier to see that the marks machined into the harmonic balancer hub.

Make sure that you set he timing when the engine is up to operating temperature.

At this point hook up all the wires, get out the timing light. Connect timing light up to battery & #1 spark plug.

Remove the SPOUT connector (do a search if you want a picture of the SPOUT connector) It is the 2 pin rectangular plug on the distributor wiring harness. Only the EFI Mustang engines have a SPOUT. If yours is not EFI, check for a SPOUT: if you don’t find one, skip any instructions regarding the SPOUT
Warning: there are only two places the SPOUT should be when you time the engine. The first place is in your pocket while you are setting the timing and the second is back in the harness when you finish. The little bugger is too easy to lose and too hard to find a replacement.

Start engine, loosen distributor hold down with a 1/2" universal socket. Shine the timing light on the marks and turn the distributor until the mark lines up with the edge of the timing pointer. Tighten down the distributor hold down bolt, Replace the SPOUT connector and you are done.

The HO firing order is 1-3-7-2-6-5-4-8.
Non HO firing order is 1-5-4-2-6-3-7-8

Step 2. ) Dump the codes & do a cylinder balance test.
Cylinder balance test: use this to find dead or weak cylinders:

Revised 25 March 2012 to add necessity allowing the KOEO tests to finish before starting the engine and the need for a properly functioning IAB/IAC to run the cylinder balance test.

The computer has a cylinder balance test that helps locate cylinders with low power output. You’ll need to dump the codes out of the computer and make sure that you have the A/C off, clutch depressed to the floor and the transmission in neutral. Fail to do this and you can’t do the engine running dump codes test that allows you to do the cylinder balance test.

Here's the way to dump the computer codes with only a jumper wire or paper clip and the check engine light, or test light or voltmeter. I’ve used it for years, and it works great. You watch the flashing test lamp or Check Engine Light and count the flashes.

Be sure to turn off the A/C, have the clutch depressed to the floor, and put the transmission in neutral when dumping the codes. Fail to do this and you will generate a code 67 and not be able to dump the Engine Running codes.


Here's how to dump the computer codes with only a jumper wire or paper clip and the check engine light, or test light or voltmeter. I’ve used it for years, and it works great. You watch the flashing test lamp or Check Engine Light and count the flashes.

If your car is an 86-88 stang, you'll have to use the test lamp or voltmeter method. There is no functional check engine light on the 86-88's except possibly the Cali Mass Air cars.

The STI has a gray connector shell and a white/red wire. It comes from the same bundle of wires as the self test connector.

89 through 95 cars have a working Check Engine light. Watch it instead of using a test lamp.

The STI has a gray connector shell and a white/red wire. It comes from the same bundle of wires as the self test connector.


WARNING!!! There is a single dark brown connector with a black/orange wire. It is the 12 volt power to the under the hood light. Do not jumper it to the computer test connector. If you do, you will damage the computer.

What to expect:
You should get a code 11 (two single flashes in succession). This says that the computer's internal workings are OK, and that the wiring to put the computer into diagnostic mode is good. No code 11 and you have some wiring problems. This is crucial: the same wire that provides the ground to dump the codes provides signal ground for the TPS, EGR, ACT and Map/Baro sensors. If it fails, you will have poor performance, economy and drivability problems

Some codes have different answers if the engine is running from the answers that it has when the engine isn't running. It helps a lot to know if you had the engine running when you ran the test.

Dumping the Engine Running codes: The procedure is the same, you start the engine with the test jumper in place. Be sure the A/C is off, clutch depressed to the floor and the transmission is in neutral. You'll get an 11, then a 4 and the engine will speed up to do the EGR test. After the engine speed decreases back to idle, it will dump the engine running codes.

Trouble codes are either 2 digit or 3 digit, there are no cars that use both 2 digit codes and 3 digit codes.

Your 86-88 5.0 won't have a working Check Engine Light, so you'll need a test light.
See AutoZone Part Number: 25886 , $10

Alternate methods:
For those who are intimidated by all the wires & connections, see Actron® for what a typical hand scanner looks like. Normal retail price is about $30 or so at AutoZone or Wal-Mart.

Or for a nicer scanner see Equus Digital Ford Code Reader (3145) Equus - Digital Ford Code Reader (3145It has a 3 digit LCD display so that you don’t have to count flashes or beeps.. Cost is $22-$36.


Cylinder balance test

If you have idle or IAC/IAB problems and the engine will not idle on its own without mechanically adjusting the base idle speed above 625-750 RPM, this test will fail with random cylinders pointed out every time it runs. The IAC/IAB must be capable of controlling the engine speed to run in the 1400-1600 RPM range. Playing with the base idle speed by adjusting it upwards will not work, the computer has to be able to control the engine speed using the IAC/IAB.

Warm the car's engine up to normal operating temperature. Use a jumper wire or paper clip to put the computer into test mode. Let it finish the Key On Engine Off (KOEO) code dump. Start the engine and let it go through the normal diagnostic tests, then quickly press the throttle to the floor. Remember to keep the clutch pedal (5 speed) depressed to the floor during the test. The engine RPM should exceed 2500 RPM's for a brief second. The engine RPM's will increase to about 1450-1600 RPM and hold steady. The engine will shut off power to each injector, one at a time. When it has sequenced through all 8 injectors, it will flash 9 for everything OK, or the number of the failing cylinder such as 2 for cylinder #2. Quickly pressing the throttle again up to 2500 RPM’s will cause the test to re-run with smaller qualifying figures.
Do it a third time, and if the same cylinder shows up, the cylinder is weak and isn’t putting out power like it should. See the Chilton’s Shop manual for the complete test procedure


Do a compression test on all the cylinders.
Take special note of any cylinder that shows up as weak in the cylinder balance test. Low compression on one of these cylinders rules out the injectors as being the most likely cause of the problem. Look at cylinders that fail the cylinder balance test but have good compression. These cylinders either have a bad injector, bad spark plug or spark plug wire. Move the wire and then the spark plug to another cylinder and run the cylinder balance test again. If it follows the moved wire or spark plug, you have found the problem. If the same cylinder fails the test again, the injector is bad. If different cylinders fail the cylinder balance test, you have ignition problems or wiring problems in the 10 pin black & white electrical connectors located by the EGR.

How to do a compression test:
Only use a compression tester with a screw in adapter for the spark plug hole. The other type leaks too much to get an accurate reading. Your local auto parts store may have a compression tester to rent/loan. If you do mechanic work on your own car on a regular basis, it would be a good tool to add to your collection.

With the engine warmed up, remove all spark plugs and prop the throttle wide open with a plastic screwdriver handle between the throttle butterfly and the throttle housing. Crank the engine until it the gage reading stops increasing. On a cold engine, it will be hard to tell what's good & what's not. Some of the recent posts have numbers ranging from 140-170 PSI. If the compression is low, squirt some oil in the cylinder and do it again – if it comes up, the rings are worn. There should be no more than 10% difference between cylinders. Use a blow down leak test (puts compressed air inside cylinders) on cylinders that have more than 10% difference.

I generally use a big screwdriver handle stuck in the TB between the butterfly and the TB to prop the throttle open. The plastic is soft enough that it won't damage anything and won't get sucked down the intake either.

A battery charger (not the trickle type) is a good thing to have if you haven't driven the car lately or if you have any doubts about the battery's health. Connect it up while you are cranking the engine and it will help keep the starter cranking at a consistent speed from the first cylinder tested to the last cylinder.

See the link to my site for details on how to build your own blow down type compression tester.

If no codes 14 or 18 found, does the miss only occur at high RPM on a warm engine? If so the PIP sensor or TFI module are suspect.

 

[elarm1]

@John Dirks Jr These test by @jrichker tremendously helped me discover my problems. I would check the timing and double check the plugs with the cylinder balance test.

 

[JD1964]

Ahhh, chasing the gremlin. I think I've figured it out. It was the new MSD distributor cap. First big change came when I removed the cap topper thing that goes over the wires. I could even see on the coil wire tower and mounting screw holes where the dust from arcing had been happening. But even with the top piece removed, the problem was intermittent. It was weird because I could cut the timing back to 8 and the problem would go away mostly. Move it back to 10 and the problem would come back, even happening as low as 4k rpm. Just didnt seem right. Anyway, I decided to put the old cap and rotor back on. That fixed it. Timing back at 10 and no issues. I'm going to test again tonight when it gets colder outside.

So, new MSD cap/rotor (suspected made in China) has non brass posts and a larger red colored counter balanced rotor. It's a POS!!!

My old MSD cap/rotor (made in USA) has brass posts and a smaller grey colored rotor. Works fantastic!!!

So beware, even if a vendor shows you pictures of the good stuff like this.

You might wind up getting junk like this.

Here are some side by side comparisons. Brass posts and grey rotor works for me. The other one causes misfires in my application.

 

[revhead347]

Always start by putting the old stuff back on and seeing if it fixes it. MSD is cheap crap. Buy an Accel next time. I have had terrible luck with Moroso wires as well.

Kurt

 

[elarm1]

Are you using an MSD Ignition (box)? I would be worried about burning up the stock terminals of the stock cap. Anybody every have problems with a MSD box and stock Cap, wires, and rotor?

 

[JD1964]

Are you using an MSD Ignition (box)? I would be worried about burning up the stock terminals of the stock cap. Anybody every have problems with a MSD box and stock Cap, wires, and rotor?

Not using MSD box. I'm using a stock style coil. Pertronics brand high output.

 

[JD1964]

Always start by putting the old stuff back on and seeing if it fixes it. MSD is cheap crap. Buy an Accel next time. I have had terrible luck with Moroso wires as well.

Kurt

10-4, Accel from here on....

 

[JD1964]

Now, I have to put the Autolite Racing plugs with trimmed ground straps back in. They were swapped out for the standard 764's in this gremlin hunt before I went back to the old cap and rotor. That swap did not solve the issue so the new plugs go back in.

 

[TOOLOW91]

Are you using an MSD Ignition (box)? I would be worried about burning up the stock terminals of the stock cap. Anybody every have problems with a MSD box and stock Cap, wires, and rotor?

Running a 6al on my car with a autozone cap and rotor . No issue


Sent from my iPhone using my fingers while my auto correct makes me seem illiterate

 

[jrichker]

Some confusion of terms seems to be circulating here...

Pinging or spark knock is not the same as detonation.

Pinging is preignition of the fuel air charge by some source of ignition other than the spark plug. The source of the ignition can be a hot spot in the combustion chamber such as carbon, a spark plug insulator, side electrode, or a sharp edge on a valve. It occurs before the spark plug can fire and while the piston is still on its upward movement towards TDC. That is the cause of the characteristic ping or ringing sound, much like shaking a coffee can full of BB’s.

Detonation is the uncontrolled explosion of the fuel air charge after the spark plug fires and starts to burn. In a properly running engine, the spark plug ignites the fuel air charge and it burns slowly and evenly across the combustion chamber, much like a fire as it burns its way across a grassy field. When detonation occurs, the ignited fuel air charge causes an increase in the combustion chamber pressure and temperature. The remaining fuel air charge that has not been burned self–ignites explosively causing tremendous heat and pressure. The source of secondary ignition can be the same as preignition, or can be simply due to the heat and pressure. Detonation is what damages engine parts because of the excessive heat and pressure.

Detonation can lead to pinging, and the results are the same: engine damage because of the excessive heat and pressure

 

[Boosted92LX]

Not using MSD box. I'm using a stock style coil. Pertronics brand high output.

I always ran mallory and had fantastic luck with them. In fact, I'm using an old mallory box on my car now that I've had for yeeeeears. I was actually having spark blow issues and it fixed the problem. The bad news? From what i hear, msd just bought mallory.

 

[revhead347]

I am running my 4th MSD Digital 6. Had some bad luck with Mallory distributors as well.

Kurt