Losing my mind with this car!

After months of messing with it and searching possibly every thread/forum/piece of info I could find on the issue I'm having, I've finally decided to post for help from my fellow mazda protege community.

Here's the issue...
Once the car warms up, it hesitates and stumbles at specific RPMs. Similar to a missfire or hitting a governor.

Here's the background to the problem...
I decided to change over to the 1.8 coil conversion and long reach plugs. (Eng is the stock 2.0 fs-de) the car ran fine before I changed everything out...valve cover from 626, coils, wires, plugs...then after the conversion it ran like total crap, stumbling all over the place, not driveable at all. Being the packs were off a junkyard car, I ordered brand new ones. Replaced them, problem got better, but still bad. Changed out the wires with another new set, no change, put in normal spec plugs, seemed to make it less erratic, but now the car stumbles at 2800-3000 rpm pretty much on the dot. Decided that many people do the 1.8 conversion, so it must be another issue. Only other part touched at the time was the swap of valve covers, so I thought that the cam angle sensor might have goofed out of no where...changed that, same issue, no change. Started changing checking sensors. Here's the list:

MAF - checked with meter/cleaned/swapped with new one
Cam Sensor - checked with meter/changed with new one
Crank sensor - checked with meter/measured clearance from teeth on pully. New one on the way, haven't changed part yet.
EGR - cleaned, checked with meter, have another one, haven't changed yet.
Coil packs - changed twice once used then new ones.
Wires 1.8 - changed with new twice first set Bocsh second set Duralast.
Plugs - new long reach spec, then new stock NGK copper .044 gap.
Intake - scanned for leaks, it's aluminum Injen cold air, so no cracks in it or connectors.
ECU - reset multiple times.
Fuel pump - new filter housing/screen
TPS - checked with meter

Basically I have ran a multimeter through the whole car and every sensor I could think of using specs from the FSM. Nothing checks bad. I've replaced a bunch of sensors, still no change. In frustration I decided to put back my old 2.0 packs and Nology wires. The problem calmed down a bit, and the car is better, but now it stumbles at around 1800 rpm and 3000 rpm range. When pressing the throttle it hesitates up slowly (about 5-7% peddle) stumbles a bit on those two rpm ranges, then revs hard after 3100 rpm as if I pushed the gas harder, not out of control fast, but normal quick vs the laggy feeling from idle to 3k. The old 2.0 packs and wires make it less harsh than the 1.8 setup where it felt like I hit a tree at 3000 rpm. This happens in all gears and the faster I punch it, the worse it does it. If I ease the gas, it's not as crazy.

Another bit of info...there are no CEL codes either.

I'm about tired of throwing parts at this thing and want to pull the motor out and smash it with a truck, so any help will be much appreciated, I'm stumped.

Additional edit:
I've also checked the injectors connection with my Noid set, and are audibly firing. Not sure how well, but when I disconnected them to check wiring with the engine running, the idle goes from bad to good once I plug the connector back in, so assuming they are fine.

PCV valve is new and works proper also. And far as I can hear and see/feel, I have no vacuum leaks.

KCKrogoth said:

Additional edit:
I've also checked the injectors connection with my Noid set, and are audibly firing. Not sure how well, but when I disconnected them to check wiring with the engine running, the idle goes from bad to good once I plug the connector back in, so assuming they are fine.

PCV valve is new and works proper also. And far as I can hear and see/feel, I have no vacuum leaks.

Click to expand...

Have you ever examined the VICS screws to see if they are all there>?

http://www.astina gt.com/forums/showthread.php?t=21145

VICS is removed, sorry should have added that

Sorry, I mean VTCS is removed, haven't checked the VICS screws, I have been sitting on a 626 manifold for a while debating on changing over to it.

I think you should do a big seafoam treatment.
It may not help but it's cheap and easy and is always a good idea.

After that I think you should consider coils... Again...
I know you've done them over and over but they affected things every time you changed them.

Coils for the P5 are a real PITA ( I don't know about the 1.8 ?) ... They can be bad brand new out of the box.

Apparently Polish coils are good ones.

I like them mmmm...

That is probably going to happen, being the ones I put back are super old. I'll order some new 2.0 packs and see if it fixes it. Only thing that I don't understand is that the car ran fine before the 1.8 conversion, so I assume the original setup would put it back to normal, but didnt. Only thing I didn't do was put the old plugs back. So might try messing with them too and see if there is a change.

No codes?

Have you done a power balance test to see if there is a misfire on a specific cylinder?

Are you positive the plug wires are going to right cylinders, and the coil plugs into the right coils? I don't know that it would run if they were wrong, but it's still a possibility.

No sure what a power balance test is, so no...but I'm positive I have the correct wire/coil combo. I believe that the car wot run otherwise and I cross referenced the FSM

I drove around for a while trying to get it to throw codes, didn't happen. Hooked up my scanner and it didn't even have any pending either.

KCKrogoth said:

No sure what a power balance test is, so no...but I'm positive I have the correct wire/coil combo. I believe that the car wot run otherwise and I cross referenced the FSM

Click to expand...

Unplug each injector one at a time, and see if each cylinder is firing.

I did that in a way with the Noid test, each time I unplugged one the engine would drop RPM then correct and go back to normal after I plugged it back in. I know this can be done with the wires on the packs too, but I don't really want to run the risk of shocking myself...done that before, it hurts...lol

If the only thing you didn't change back was the old plugs, perhaps that's your problem. If the plugs aren't gapped correctly, it makes a huge difference with these FSDE's. Or maybe since the 1.8 coils are not oem, then you need to gap the plugs to go with the 1.8 specs and not the original 2.0 specs.

I have thought about that. In fact I dug out the long reach plugs I had in it with the 1.8 coils and was gonna try that combo with the 2.0 coils, but I've been at work all weekend and haven't had time to deal with it yet. Was going to get a set of new NGK V-power coppers also, since I tossed the original plugs a long time ago. I'm wondering if it doesn't like the laser platinum plugs that are in it now, which is strange, because I have always run NGK PFR5G-11 plugs in it with no problems.

Little bit of further info to the above, did a quick bit of research...the 1.8 and 2.0 engines require the same plug gap. However, i belive your theory is not invalid...I'm still going to swap plugs around and see if it changes. I've seen stranger problems solved with dumb answers, for example, my old FD had bucking issues that were solved when I tightened up the negative battery terminal. [emoji6]

OK... Here's my guess...

Perhaps your injectors are slightly fouled creating as shity spray pattern, then mixed with a potentially weak spark from marginally effective coils that begin to fail at that specific rpm, you get missing and lagging.

Then... perhaps... your cylinders and injectors became more fouled... enough that switching back to your original setup didn't fix it... ????


+1 on the copper v-groove plugs... They give the most reliable spark. You just have to gap them and change them more often.
They may make the difference you need.

If not there is a handy tool tool to help you remove your engine to run it over with your truck.

Can your scanner read live data? If so, what are your fuel trims?

No, unfortunately, just a basic OBD II reader

NGK PFR5G-11 and most of the other plugs for the FSDE are pre gapped at .044". I have an MSP and I ran the NGK PFR5G-11 at one point. My car ran pretty bad with them. I did a little researching, and found that the FS-DET is supposed to have a .028" - .032". I regapped the plugs it ran great. I found that the FS-DE plugs are supposed to be gapped at .040" - .043". My wife has a 2002 P5 and I gap her plugs @ .040" and her car runs good. Try re gapping the plugs, it may make a huge difference.

polaris said:

NGK PFR5G-11 and most of the other plugs for the FSDE are pre gapped at .044". I have an MSP and I ran the NGK PFR5G-11 at one point. My car ran pretty bad with them. I did a little researching, and found that the FS-DET is supposed to have a .028" - .032". I regapped the plugs it ran great. I found that the FS-DE plugs are supposed to be gapped at .040" - .043". My wife has a 2002 P5 and I gap her plugs @ .040" and her car runs good. Try re gapping the plugs, it may make a huge difference.

Click to expand...

I will give it a shot.

Here is where I'm at currently: Replaced the plugs back to the Long reach coppers and it got rid of the stumble at the lower RPM and consolidated it back to the 3000K mark again. Car drives slightly better on the longer plugs than the platinums, but only slightly. It still slams pretty good if you give it any kind of decent throttle (not stomping it, but not grandma pushing it either). I took a video of the car at idle to show what is going on, and hopefully help out the troubleshooting. Once it's finished uploading I'll post the link.