Spark vanishes with throttle input

[M2cupcar]

I've just installed a salvage-yard fresh 03 v6 in my 626 ES 5spd. It idles perfectly and will increase revs with the slowest throttle input. BUT if there's any load or any quick throttle input the spark vanishes. Every sensor has been scoped on the car and registered within spec. No signals appear out of the ordinary. We've swapped parts from the old motor that were working onto this motor and nothing changes. It's got the usual fresh parts: cap, rotor, plugs... cam timing has been checked and rechecked. Any and all suggestions are appreciated. I need inspiration, my brain hurts.
thanks,
rob

[Denny]

Did you swap vafs? I would think you had a vacuum leak except you said it idles perfectly. Maybe squirt some oil around the intake manifold or throttle body and then rev it to see if it temporarily seals. Throttle cable adjusted right and not hanging up? Oh, check codes and see if any crankshaft thingies come up.

[SLEEPER 626]

Did you try replacing the plug wires?

They could be arcing to each other causing interference.

Good Luck with the Gremlins!

[M2cupcar]

What's a vaf? Tho it prolly did get swapped. Plugs & wires are fresh. No vacuum leaks period- and we've double (maybe triple) checked all the vacuum routing. To top it off there are no codes being thrown (of course). Seems like the car threw codes when nothing was wrong and now it wouldn't throw a code to save it's life.

The only suspect signal is the distributor coil trigger. The tech's theory is that on the old motor the compression was low enough to tolerate a weak spark. With the new motor and higher compression the weak spark is literally being overcome or extinguished by the compression. He followed up by saying this is why some cars need ignition upgrades for a stronger spark when upgrading to higher boost systems (turbos etc.). Sounds legit too me- and keep in mind we are "reaching" for ideas here. And there's no sensor monitoring the distributor to trigger a code. Of course this requires me to pick up a disty and try it out. Their parts guy wants 275 plus core- so I'm probably headed to mazmart.

Thanks for the suggestions. Be sure to post any more if you have a brainstorm regardless of how outrageous. - rob

[luiz gouveia]

Hey, we have the same problem. After I took the intake manifold out for the polishing and porting. Then when I was putting it back , it was very dark in the garage and I did not see that the knock sensor wire got smashed between the upper and lower manifolds. After that, I've always thinking that could cause that to damage other parts on the car like The ECU, or coil. Like you did , so far every thing have been tested, The shop that I took the car yesterday told me that is a vacumm leak or the Injectors. I will let you know if I find the problem. GOOD LUCK...

[M2cupcar]

Luiz- we've swapped the injectors and it made no difference. Also have tested with and without the knock sensor and scoped the sensor- which checked out ok. I probably won't pick up the disty 'til tomorrow. I'll report back after that. My original concern was that perhaps the vacuum lines had been hooked up to wrong spot- wouldn't give the symptoms of a leak, but would surely cause problems. But we've double checked that. - rob

[Denny]

The vane airflow meter (vaf) measures the air coming into the air intake and and sends a measured amount of air to the engine. If anything leaks after the vaf, the car won't run right. Btw, it's the blk metal thing between the airbox and the throttle body.

[M2cupcar]

doh- got it. Yep, it was checked. We put a scope on it and then checked voltage while moving the vane (plunger?) and it was within spec. I was sure that was the problem at first, as I've had similar issues with other flow meters on other cars- and based on the symptoms it seemed obvious. Unfortunately I'm not that fortunate.
- rob

[M2cupcar]

As promised I'm reporting back. The problem is solved- bad distributor (actually the coil). Unfortunately you can't buy one without the other. So I got a new Mazda distributor assembly for a "shop" price of $270 and that was the very best deal going. For some reason the Ford dealers wanted over $500 for the Ford part. And there's a core charge regardless of who you go to for $65. I didn't see anything on the list, but according "some" Mazda service guys this is a very popular item.

Now here's what to look for:
The car would idle beautifully. It would rev only with the slightest throttle input. I'm talking like maybe mashing the pedal a tenth down nothing more. Any more input would cause the spark to go to crap and to the point that it wouldn't even trip the timing light. Trying to move the car in gear (introducing load) and the same problem would occur. Running a scope on the coil signal produced an incredibly jagged signal... I'd like to compare it to those jaggy dyno plots you see on cars that have a poor spark, but this is worse. Problem is that it was still showing a trigger... and that was enough to make any tech think that it possibly might not be the cause. But it was.

Hope this will be archived and save somebody a little grief. Thanks to those who made suggestions. - rob

[Rick_96PGT]

To the archive batman

If anyone takes the time to read this, you will find a few methods used to solve this particular problem. In the end only one resolution is valid.

-Copied to the Archive