Okay, time to ask a question. I suppose my 88 coupe is jealous of all the work being done to the 88GT. Affectionately I call her the red-headed step child. I've been driving the car going on five months. At idle it has an intermittent miss. I put new spark plug wires on the 88GT, universial fit MSD, and had enough left-over to do the 2.5L. Also, I had been running Bosch Platinum plugs, but had read about difficultly with the DIS 2.5L cars. Today, I put the wires and a standard set of AC Delco plugs. BTW, the +4 Bosch Platinum plugs looked okay - I was expecting something bad. Idle is much better, but now it intermittently misses at speed.

When I got home tonight I checked the new wires with my VOM and all are under 200 Ohms as they should be, 40-50ohms per for for MSD 8.5mm wires.

I'm just wondering if going from graphite wires to spiral core low resistance wires could exacerbate a weak coil?

Suggestions?

I have a spare set of unknown condition that will be swaped with tomorrow. Suppose I should test the crank position sensor while at it.

Fiero - it's not just a car, but an adventure!

Intermitant miss could also be loose/dirty harness on the ignition brick.

I think the brick has a ground running to a bell housing bolt near by. make sure that's clean and tight.

Check all the other stuff bolted to the block as well.

Could be a new wire or plug bad. could be a coil on the edge. Could be allot of things.

You can get whole bricks cheap from salvage yards. 87-88 Grand Am and 87-91 Olds Cutlass Calais. grab 2-3 of them.

lots of DIS stuff in my cave...

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11-Sept-01, The day the world as we knew it ended.

Tonight I took the DIS brick out. Crank positon sensor was cracked, but functional. It was one of the "since you are at it moments", sensuous moments; replaced CPS.

Tested the MAT, used VOM and hair dryer/refrigerator freezer. Tested the TPS. Tested the primary resistance of the coils.

"I think the brick has a ground running to a bell housing bolt near by. make sure that's clean and tight."

What ground? Does it connect to the 13mm bolt with a stud? ARG! I think the previous owner was not too intelligent.

Solution was to put the old plug wires back on. Runs same as before. Left the Delco plugs in and I can't tell a difference in how it runs versus the +4 platinum plugs.

I'm fairly sure the problem is and issue with the connectors I used on the DIS brick end of the MSD wires. I used standard ends left over from a set of Accel wires put on the Jeep. The MSD wires on the 88GT work GREAT, each end the conductor has its own crip as well as a jacket surround crimp. The ones I used on the 2.5 car were bend around standards. I'm betting it was the connector and an inefficient crimp; not a direct crimp to the conductor.

I'm going to get four MSD style ends from the shop and try it again. If the problem persist with the new wires I'm going to run the Delco wires and be happy with the daily driver as is. 32+MPG around here and better on the highway.

The wiring harnes connectors to the brick lock tabs are broke. Suppose it would be wise to fix so I don't have a loose wire problem. Arg!

Old Adage - if it is not broke don't fix it.

BTW, good reading in the cave - excellent DIS links. Frantic once over read...

QUESTION

Just clear up one issue. In one plug pair does one plug, the same plug, always fire backwards? Or is it the waste-gate plug that fires backwards? This would imply the compression stroke cylinder fires normally, and the waste-gate backwards; they would switch next cycle.

[This message has been edited by mindscape (edited 02-06-2002).]

quote Originally posted by mindscape: Or is it the waste-gate plug that fires backwards? This would imply the compression stroke cylinder fires normally, and the waste-gate backwards; they would switch next cycle. [This message has been edited by mindscape (edited 02-06-2002).]

Exactly!

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James Essar
Co-Founder of NEO Fiero Club!
Stock 4, Wanna Race?

are you speaking of an actual miss...i mean it sounds like the cyl is actually not firing...or a kind of sputter noise. i have no idea and ive been working on them for years but almost all 2.5s have a lil sputter at idle, even when brand new. if that's what youre talking about........youre wasting your time. personally i think it has something to do with the design of the intake manifold, but thats just a guess. if it's a true missfire then id bet on a bad coil. let me know which it is.........curiosity.

phil

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GTDude 87 Fiero GT 3.4
25 years GM experience

Update, I recrimped the ends of the MSD 8.5mm wires for the 2.5L car. Next, I checked the resistance, good. I'm a nightowl, so back on the car they went. Same problem, cruising, open up the throttle up and MISS. So, I'm like, ARGH! Again, I put the Delco/Packard 7mm graphite wires back on AND all is well.

DIS is a picky critter. Now I want to know why they do not work with DIS, as I am CERTAIN the wires are good; crimped properly etc.

I'm going to give the fellows at MSD a call on their tech line. I'm expecting them to say the 8.5mm super conductor spark plug wires are not DIS compatible.

However, I almost would be certain the Accel univeral fit sprial core 8mm wires will work - more resistance. Whereas the MSD super conductor have around 40-50 ohms per foot, the Accel have about 50 ohms per inch. For the curious, the 8.5mm MSD wires madeup for 2.5L range in resisance from 150 to 100 ohms per wire.

Now I suspect it is a DIS loading issue. I'm guessing more of the voltage is being sourced over the waste gate instead of the discharge plug. Yes, this suggest that my wires are backwards. (Argh! It's cold, do I swap them and try it again? Maybe??)

Just to be on the safe side, plug wire order on the DIS brick is 2/3 and 1/4 top to bottom; that is how the coils are labeled. IS THIS CORRECT? (I'll do a search before going to sleep.)

YES, I tried a spare set of coils - no change.

Interesting problem....

interesting problem there.....yes the coils are 2/3 1/4. did you replace the module when you replaced the coils.....as an assembly. its rare but i have seen a module act the same way. does it miss all the time or only under a load? If you replaced the coils and plugs and crank sensor and module......nothing left...has to be bad plug wires......sorry

phil

Phil - it ONLY misses when I have the MSD 8.5mm super conductor wires on the car. Idles fine, lower RPMs okay, but for example, when in 5th gear open the throttle up - wide open, it misses. NOTE -> It does not MISS when using the Delco/Packard 7mm graphite wires. Repeate, IT DOES not miss with the Delco WIRES.

I took the MSD wires to the shop today and they are confimred as being assembled correctly; second opinions are good.

As an experiment, with the Delco wires, I switched the wires, instead of 1-4 to 4-1, and 2-3 to 3-2. Running the car I can tell no qualitative difference.

theorge mentioned a ground wire that my car is apparently missing. There is a bolt with a stud on the bell housing - no wires/nothing - and a bolt with a stud on the DIS brick - no wires/nothing. I'm going to run a ground wire to the stud on the DIS brick bolt; can't hurt.

No answer from MSD tech, yet. Decided to email instead of calling it in. This car is my daily, and the Delco wires work just fine, so it's just an enigmatic issue as to why the MSD wires don't work well.

They may have moved the wires for 88. Mine is an 87.

Go over the block and bell housing. Check every wire bolted to them. I've got a couple on the head and two differant places on the bell housing. (I do this periodically just to be sure... read Wire Service in the cave.)

Plus the big one from the battery and the braded job that goes from the block to the body.

DIS is crabby about things. It only is a problem when the MSD wires are on... It doesn't like something about the MSD wires... no surprise.

Yes. one plug in each pair, the same plug, is always fired in reverse in this version of DIS. (Delphi does have a version that reverses the coil polarity with each firing but this isn't it.)

1/4 and 2/3 must be paired on thier respective coils. As you've seen it makes no differance which way they are polarized on the coil.

The +4 plug may be better with DIS... I think most people have had the problems with the regular Bosch platinums. Since most of the +4 design appears the same as the regulars I felt it was better to be safe and recomend against them, especially at that price.

In reality DIS is perfectly happy on standard plugs. Autolites are waranted for a 3 year life no matter how many miles. I don't see any plug that's really any more "open" than the .060 OE gap specification. +4 plugs have a big gap but around 180 degrees of the arc path are shrouded in the plug.

The only platinum plugs I'm considering ever testing are either AC or Autolite "double platinum" ones. Those put a pad on the ground electrode that effecively makes it a second tip just like the center one. It should improove the effecivness of the backwards firing plug.

Lastly,,,, the DC resistance of a plug wire often doesn't mean a whole lot in the real world. Standard HEI runs around 30Kv and DIS is up around 40Kv. These high voltage behave much differantly than the few volts DC used by an Ohm meter.

I hate to send you to a manufacturor site but they have one of the best short explanations of this I know of online. Magnecor You could, and people have, write volumes about this.

Update, I've recrimped the ends and load tested the wires. Load testing consisted of using a 9V battery and a VOM. Next, each wire was swapped in place of one wire on my 88GT car with HEI. THE WIRES ARE ASSEMBLED correctly; 40-50 ohms per foot as indicated in the instructions.

I took the wires to the performance shop where they were bought. They checked them and were puzzled, like there is no reason why they should not work. Well, in fact they do work, because the car starts, idles and acclerates. HOWEVER, the car misses under the following scenario predictably. When cruising at 55MPH in 5th gear, open the throttle wide open the engine misses. Swap back in the Delco graphite wires and the miss does not occur.

The following quote is the reply I recieved from MSD technical support.

> Dear Sir;
>
> It shouldn't matter whether you have a DIS or not. Our Super Conductor
> will work on just about anything. They are used on everything from stock
> street vehicles to 6000HP top fuel cars. It may be that you have a bad wire.
> Check the resistance on each wire. You should see 40 to 50 ohms per foot.

I wrote MSD tech back and refered them to this thread for more information.

theogre - thanks for clearing up the polarity issue on the Fiero DIS ignition. I did not think that it changed polarity. I think that because one plug fires forward, anode to cathode, and the other cathode to anode, the Autolite Platinum Pro plugs would be ideal for Fiero DIS equipped engines because of their dual ignitor pad design.