1995 2.5l V-6 Missing......uh oh, now mine's doing it!!!!!

[rufus 0]

[MaddMike 0]

Change the plugs and the wires. They are 13 years old. Even though you only have 38k on the car age still takes it toll. As for being a reliable car, my 98 SE V-6 hit 182k before it spun a bearing.

Edited October 20, 2008 by MaddMike

[Terry Haines 90]

[rufus 0]

In this case of a misfire I'm sure you must have a code stored in the EEC and a check engine light..We need that code asap...

 

No light, so I haven't had the EEC read for a code.

 

Thanks for the help!!

 

Bob....

[rufus 0]

The ign system is a a 'wasted spark' design and fires TWICE per cycle ,a conventional induction timing light will not work on a plug wire..

 

Terry - I was assuming my inductive light would pick up the extra firings, but would still show a continuous, steady series of flashes at twice the normal frequency (i.e. 800 rpm would just look like 1600, for instance)......this isn't right? What is it that doesn't work with a 'wasted spark' ignition system? ....in using the light on it at idle, it appeared to flash normally most of the time, but occasionally would either skip or drop out (this is the only thing so far that lead me to conclude my problem is in the ignition). ....or does an inductive light somehow flash randomly with a 'wasted spark' ignition giving totally erroneous results????

 

Bob...

[Terry Haines 90]

The plugs spark twice per fukll cycle.Once at the correct position XX degrees BTDC for the normal ign and a second time around the exhaust valve open position..This is normal on such ign systems with coil towers.No way can a normal timing light establish which is the geunuine ign spark...

 

Without any codes I'm tempted to say 1)This is not a genuine misfire 2)Check engine light bulb is blow...I'd still suggest you have the EEC read for any active/stored codes..I'm sure you will find some despite no light on...

[rufus 0]

The plugs spark twice per fukll cycle.Once at the correct position XX degrees BTDC for the normal ign and a second time around the exhaust valve open position..This is normal on such ign systems with coil towers.No way can a normal timing light establish which is the geunuine ign spark...

 

I see, an inductive light just can't be used to set/read ignition timing, because it can't distinguish between a real and false event. But since I'm not trying to read or set timing (I'm just looking at the flashing light to see if the light flashes steadily), it should work for me, right? I.e. If the ignition system is functioning properly, the light should flash steadily w/o dropping out, right? Therefore, as I've observed, since the light does drop out every few seconds, then the ignition system is missing. Or is it me that's missing something???

 

I'm sorry for being such a PITA. Anyway thanks for your help!

 

Regards,

Bob S.

[Terry Haines 90]

...to fully understand.

 

The V6 coil tower assy has THREE coils, ech coil fires TWO cylinders at a time.Linked cylinders are #1 to #5, #2 to #6 and #3 to #4.

When the mech side of the engine(piston,valve position etc) is correct for say #1 ign then #5 is on it's exhaust strok...so a spark on ign stroke,#1 is at 10deg BTDC then #5 is at 10deg BTDC on EXHAUST stroke...BOTH plugs spark at the same time..and so on thru the whole firing order of the engine..So when #5 is on 10deg TDC compression stroke #1 is at the same position AND sparks but on exhaust stroke....

This is why we have double plat plugs..due to one bank being '-' polarity and other bank with '+' polarity. When the cars were new one bank had factory fitted single plat plugs the other twin plat plugs for the very reason than one sparks centre to ground ,the other ground to center...esay eh!!(now we fit double plats on all cylinders to save any mix ups!)

[rufus 0]

So if there's any missing at all, the CEL should light? I'll have the EEC read.....

 

So, other than plugs, plug wires and wiring harness, what are the most frequent (likely) cause(s) of ignition missing on the V-6? Are there any electrical tests that can be done on the crank position sensor, coil, ignition module, PCM with a digital volt-ohm meter? (I can't imagine there'd be any test on the PCM!)

 

As an aside, if #1 and #5 are both fired at the same time and one is at 10 BTDC on compression and the other at 10 BTDC on exhaust, I still don't see why an inductive light won't indicate timing accurately.....it's gonna flash twice for the cylinder it's on relative to a crank marker.....once at 10 BTDC Exhaust and once at 10 BTDC on compression, BUT both look the same when observed as a flash that illuminates the crank mark.......it's just gonna 'show' 10 BTDC twice instead of once.

 

Bob....

Edited October 20, 2008 by rufus

[BuckeyeSVT 77]

Here's the deal.

 

Yes, you can check the ignition timing on the 1995 2.5L. Pull the spout plug (next to the EDIS module on the right side firewall - near the strut tower) and then at warm idle check the ignition timing. It should read 10 BTDC. However, even if it's off there is no adjustment for this system - Checking it is a moot point.

 

Be very careful on the 1995 engines, not only is wiring a big issue - The fuel injector bottom seals are also a very sore point. They are like a flat round seal that seals the injector to the LIM and I've seen alot of them because of age crack and cause lean misfires. It's tricky to diagnose unless you know the cylinder misfiring. Since you are 1995 MY you will not have misfire diagnosis in the PCM (pre-OBD2) - However you can perform a cylinder balance test if you have a good scan tool. This will tell you which cylinder isn't pulling it's load. Otherwise, it's trial and error pulling plug wires to see which cylinder isn't affected.

 

-Dom

[Terry Haines 90]

..I'd want to establish which cylinder is misfiring first.A check on all spark plugs, wires etc should be a good guide.As to the timing light,I take your point but have yet to see an old style t/light operate correctly on a wasted spark system.Try it on #5 plug wire and see what you get...

[rufus 0]

As stated in my first post, I've looked at all 6 cylinders and they ALL drop out.

[Terry Haines 90]

...in which case I would check the wiring to the plug on the crank position sensor and the wiring on the multi pin plug to the coil pack. As we all know,wire harness faults & issues can happen at any time on these cars...as you have a '95 you are in the 'high risk' class...

[MaddMike 0]

The horse is dead, quit beating on it. Change the plugs and wires.

 

Some things do not need to be over analyzed. The time you have wasted checking this and testing that, posting questions has been for naught. Your car is still not fixed. Plus your still no closer to an answer. The fact is you have a 13 year old car, nothing lasts for ever. Spend the money! Autolites for your car are about $3 each, MotorCraft the same, so thats $18. The wires you have several options. Stock replacements are fine, MotorCraft or Autolite are good both are in the $80 range and work just fine, stay away from discount wires. You can go with performance wires, as long as you stay with 8mm you will not have to modify your stock hold downs, I ran the FM 9mm($54) and they lasted about 2 years. I'm currently using Taylor 8.2($64 and they fit my stock hold downs).

 

If installing the new plugs and wires takes care of the miss, great mission complete move on to the next level. If not, you have replaced two things that needed replaced anyway and you will know more than you did before.

[Terry Haines 90]

...from what he has said,and I missed it,ALL 6 drop out so I doubt every plug and wire is at fault.I still feel we may have a signal issue here causing the drop out of feed etc to the coil...

[rufus 0]

Thanks Terry - That's exactly the kind of guidance I'm hoping for.

 

Now as far as inspecting the wiring leading to those 2 connectors.....am I correct that it's a matter of peeling back any wire loom to look for deteriorated (brittle, loose or ??) insulation and therefore bare wires underneath? What about the possibility of poor continuity at the connector itself?

 

Anyway, I'll be really gentle with the wiring as I look it over.....

 

It's probably gonna be a few days before I have any answers, since I have my '67 Corvette on the lift now for some rear suspension work.....

 

Regards,

Bob

Edited October 20, 2008 by rufus

[rufus 0]

Update: EEC shows no codes.

 

More after I have a close look at the coil and crank sensor connectors.....

[rufus 0]

Here's the deal.

 

Yes, you can check the ignition timing on the 1995 2.5L. Pull the spout plug (next to the EDIS module on the right side firewall - near the strut tower) and then at warm idle check the ignition timing. It should read 10 BTDC. However, even if it's off there is no adjustment for this system - Checking it is a moot point.

 

Be very careful on the 1995 engines, not only is wiring a big issue - The fuel injector bottom seals are also a very sore point. They are like a flat round seal that seals the injector to the LIM and I've seen alot of them because of age crack and cause lean misfires. It's tricky to diagnose unless you know the cylinder misfiring. Since you are 1995 MY you will not have misfire diagnosis in the PCM (pre-OBD2) - However you can perform a cylinder balance test if you have a good scan tool. This will tell you which cylinder isn't pulling it's load. Otherwise, it's trial and error pulling plug wires to see which cylinder isn't affected.

 

-Dom

 

Dom - Are you saying that a misfire on a '95 w/OBD1 should trip the CEL and show a code, but just not offer any diagnosis of the cause?

[rufus 0]

Edited October 25, 2008 by rufus

[BuckeyeSVT 77]

1995 models have no misfire detection capabilities, therefore it will not flash the check engine light.

 

Does the car stutter (misfire repeatedly once accelerating from a dead stop for a short time?) while driving? If so, the plugs may have succumbed to carbon tracking on the outer porcelain and that will create a misfire that will be hard to detect. Remove the plugs from all the cylinders and inspect the porcelain section. Any black lines or burn marks means you have carbon tracking issues.

 

-Dom

[Guest KAOS_2.5M]

I'd still change the plugs. it's a cheap thing to knock out.

 

I had something similar and a set of plugs temporarily cleared it up.... it later turned out to be a bad headgasket....

[rufus 0]

O.K., I'm convinced. I'll put in a new set of plugs and wires, and report what happens. (I don't like how the wires for the left bank make a sharp bend inside the plastic "loom".)

 

And what Dom described above sounds just like what happens.....off idle and under load.

 

Thanks for the input.

 

Bob

Edited October 26, 2008 by rufus

[rufus 0]

New Autolite double platinum plugs and wires, and the problem is fixed! Thanks guys!!!!

 

Obviously this is a pleasant surprise.....my '93 Mustang Cobra still runs fine on its original set of wires at 201,000+ miles. And double platinum plugs last 100,000 miles. Wow!! The 'wasted spark' ignition must be tough on plugs and wires!!

 

 

Regards,

Bob

Edited October 26, 2008 by rufus

[Guest KAOS_2.5M]

I think you owe mike an apology.

 

glad to see it's all better.