Weak spark, have fuel, No DTCs, no start.

[89turborunner]

89 7MGTE, stock except exhaust + FMIC. Installed in a 1989 4runner. Has about 10 miles and an hour on a rebuilt engine. I made new strong grounds for the head and the ignitor, and they measure fine. It ran beautiful (at 50F to 80F ambient), with no codes, and then I did the following before I was going to drive it over an hour to new garage for finishing touches on the chassis:

• 
  Fixed the heater motor (removed ECU for access)

• 
  R+R CPS (fixing leaky gasket)

• 
  Replaced leaking heater core line (lowered engine 2" for access room)

• 
  No-start condition. Fuel and spark both present. Cleaned wet (from gas) spark plugs with a propane torch. No start. Re-installed CPS and the beast fired right up, idled great, revved great (at 28F ambient). shut down.

• 
  Tried to restart. Fuse blew for dome light. No start. Code 11.

• 
  Diagnosed very bizzare electrical problem to a weak battery ground connection. Cleared code. Still no start, still no codes.

Weak spark: With the ignition "on" and a spark plug out of the cylinder, my #1 plug seems to spark erratically when I turn the CPS with the engine on TDC for #1. It will "click" and make a little puff of smoke instead of sparking, and then it will spark the other half of the time. Without a plug in the high tension wire, it will easily arc a half an inch. I can only get the system to fire (plug or not) about half of the time the CPS passes through the point when it should tell the coil to fire. It seems to not fire at all if I move the CPS slowly.

When I try to start the engine, it fires a little bit, and the tach registers. Sometimes it starts and immediately dies.

My plugs are not very old at all. Can they foul this quickly? The temp is now 30F ambient. I also have high tension wires (FSM term for spark plug wires) of unknown age. They are flexible and have never given me trouble before. Any ideas?

 

[thedave925]

Here's some ideas:

New spark plug wires?
Are the spark plug wires well insulated?
Minimize/eliminate spark plug wire contact to any other part of the engine the spark plug and coil pack. That includes other spark plug wires.

Positive that the cps is set correctly? Base timing is 10 degrees with the Diag Box terminals Te1 and E1 jumped, and a timing light.

Link to TSRM

Better yet, diagnosis page

Double check you didn't leave a block ground disconnected from when you lowered the engine.

Hope that helps
-Dave

 

[IwantMKIII]

First off, nice post

Second: My first thought was loose connection with CPS wires. Make sure they are all in excellent condition and full contact points are met

As for the weak spark, attempt interchanging the spark plug wires from another cylinder and see if condition changes

If neccessary, use a wire from another car if you suspect all wires are bad by some random chance.

Don't forget, when diagnosing, its 1 coil/2spark plugs. One spark will be strong while the other weak on 1 coil.

Further:
If you still suspect weak spark, check resistance of the coil itself and make sure it is within spec per TSRM. IIRC avearge is around .6-.8 range with the TSRM spec calling for a broader range.

Check to be sure all coils are receiving 12V from the ignitor.

Also, check for the ground from the coil pack to the head, it is still debated whether this wire actually makes much of a difference besides in theory.

 

[89turborunner]

Here's some ideas:

New spark plug wires?
Are the spark plug wires well insulated?
Minimize/eliminate spark plug wire contact to any other part of the engine the spark plug and coil pack. That includes other spark plug wires.

Positive that the cps is set correctly? Base timing is 10 degrees with the Diag Box terminals Te1 and E1 jumped, and a timing light.

Link to TSRM

Better yet, diagnosis page

Double check you didn't leave a block ground disconnected from when you lowered the engine.

Hope that helps
-Dave

The wires are well insulated (Like they haven't shocked me yet). I don't think they are the culprit since my problem came a little sudden for it to be that. But if they have them at the auto parts store, I will probably buy them just to eliminate them.

I am NOT positive the CPS is set correctly. I like to think of my self as competent, but the darn thing is so easy to put in one tooth off. Supras seem to not really run when they are one tooth off. So before I posed on here I tried it one tooth adveanced, and one tooth retarded. Seemed the same, a little sputtering, no start.

And I set the crank to 12 degrees (per my FSM) BTDC, and then did the old trick with the IG "on" and turned the CPS till I got a spark on the #1 plug with it grounded, and I am able to get it to spark in two different places in the travel of the CPS. And neither position allows the engine to run. (I do know where it should be, within about a sixteenth of an inch... I have used a timing light on it before).

Has anyone had plugs go bad with so little run time on them? It is a long drive to get some more... and on christmas eve too.

 

[89turborunner]

First off, nice post

Second: My first thought was loose connection with CPS wires. Make sure they are all in excellent condition and full contact points are met

As for the weak spark, attempt interchanging the spark plug wires from another cylinder and see if condition changes

If neccessary, use a wire from another car if you suspect all wires are bad by some random chance.

Don't forget, when diagnosing, its 1 coil/2spark plugs. One spark will be strong while the other weak on 1 coil.

Further:
If you still suspect weak spark, check resistance of the coil itself and make sure it is within spec per TSRM. IIRC avearge is around .6-.8 range with the TSRM spec calling for a broader range.

Check to be sure all coils are receiving 12V from the ignitor.

Also, check for the ground from the coil pack to the head, it is still debated whether this wire actually makes much of a difference besides in theory.

Thanks. I was trying to be judicial with my words and give enough info.

I had no idea wasted spark systems had different spark intensities as you describe. So the spark at TDC exhaust is lower voltage than the TDC compression spark? For the spark testing, I was just putting the crank timing marks on... But I did follow the TSRM for installing the CPS, so it is not installed 180 off.

CPS wire condition? They are about as brittle as 10 year old cedar. I am going to make a new wiring harness this summer.

I will check the 12V at the coils... thanks.

 

[IwantMKIII]

^IIRC, its the right output of the coil that has the weaker spark IE, spark 6,5,4. I have experimented with this on numerous turbo supras and always found the same thing. I never suggested you were 180, im trusting you followed the TSRM appropriately on that one.

The CPS wires are a VERY common problem to go bad on these cars, i'd check those first since you said sometimes the car started and sometimes it didnt.

Next time it doesn't start, check the tachometer. If the RPM's don't move while cranking, its the CPS wiring most likely.

 

[89turborunner]

^IIRC, its the right output of the coil that has the weaker spark IE, spark 6,5,4. I have experimented with this on numerous turbo supras and always found the same thing. I never suggested you were 180, im trusting you followed the TSRM appropriately on that one.

The CPS wires are a VERY common problem to go bad on these cars, i'd check those first since you said sometimes the car started and sometimes it didnt.

Next time it doesn't start, check the tachometer. If the RPM's don't move while cranking, its the CPS wiring most likely.

I always watch my tach while I crank. And it always moves while I crank : ( I don't think that is my gremlin.

Your coil output info is not what I originally thought you were describing. thanks for clearing that up.

Tomorrow morning I will do this:

1. Go buy new plugs, and wires if they are available (install).
2. check resistance on coil pack ground
3. Check for voltage at coils
4. Check coil resistance per TSRM
5. Volt/Ohm mater inspection of ECU (oh I hope I don't have to)

Now for some rest. This starts early!

 

[IwantMKIII]

id move #1 between #4&5

 

[89turborunner]

All 3 coils are at .4 ohms (.3-.5 TSRM)
12.28V at all 3 Coil plugs
Infinite resistance to ground at all coil terminals (no shorts)
12.28V at the ignitor
151-153 ohms on all 3 pickup coils in the CPS (within TSRM spec)

Still haven't gone to buy spark plugs. Any ideas?

 

[89turborunner]

Don't know how. 1 year old NGK BCPR7 plugs fouled with about 4 hours of total engine run time...

Put some champion coppers in it (I don't like champion that much, but they were new and available on christmas eve).

Now I can have a merry christmas. Thanks for your input everyone. Happy holidays.
:biglaugh::biglaugh::biglaugh:

 

[IwantMKIII]

^check your AFR's, its really the only thing that could foul them so quickly

Merry XMas