hesitation/bogging under 2500 rpms

[eyeballs]

I've had my car since last weekend, and apparently I missed this hesitation issue during the test drive. Seems to happen under 2500rpms and at moderate throttle (light acceleration is smooth). It is a fairly significant hesitation/bogging and I bet if I don't back off the throttle it would stall. I can back off, accelerate lightly to higher rpms, then it is fine. It also seems to be intermittant.

The vehicle is a '99 base model. 130k miles. Wires were recently replaced with magnecor, and I just put in new plugs 2 nights ago. No CEL. Engine is stock with the exception of intake, header, and exhaust.

I posted up on miata.net as well. So far the coil pack is the only suspect I can think of (it has not been replaced as far as I know, and my research has shown they are prone to failure and can cause hesitation), but due to the expense I want to hear some suggestions as my mechanical abilities are not the greatest.

Thanks.

[d.dutton9512]

Plugs/Wires, you can do the whole job for 40 bucks, it's easy, and it's much more likely than a coil pack.

These cars (at least in my experience) go through wires fairly often.

[Doppelgänger]

Drew, you have not had the joys of owning a 99
It's most likely that damn coil pack. I had an issue ith my 99 which turned out to be the clip that holds the harness plug to the 1-4 side of the coil. A good tap when it was running funny would fix it. Or you could find a 99 at a dealership and take it for a test drive and swap it out

[d.dutton9512]

Nope, sure havent, just going on experience. Good to know though when I start shopping again.

[jzilla]

Originally Posted by d.dutton9512

Plugs/Wires, you can do the whole job for 40 bucks, it's easy, and it's much more likely than a coil pack.

These cars (at least in my experience) go through wires fairly often.

plugs and wire.

make sure you have good wires. contact rspeed.

[Leafs8911]

This may be the issue with my car..... it never seems like it's going to stall, but in first gear, under moderate throttle, it seems like there is some "hesitation" or something I can't really describe. and yeah.... it's a '99. I'm about to go drive it again to see if I can better describe it.

[amaff]

It's probably the coils & plugs, but I had this issue on my miata when I got it. Turned out to be a botched timing belt job, and the exhaust cam was 1 tooth off.

[blackmamba92]

can you smell any fuel? Timing or coil is my suggestion. Rspeed had a used one for mine. Try them to help part cost.

[eyeballs]

Plugs and wires were recently replaced. I do smell fuel but from what I can tell it doesn't seem to be coming from under the hood. More so in the interior (fuel pump incorrectly installed? prev owner put in a new one).

You guys are fast, I was not expecting so many replies so quickly!

[RotorNutFD3S]

Experience with Magnecor wires is that they rarely have issues, when they do, they can be replaced for free under the lifetime warranty. Since you have brand new plugs and assuming they're gapped correctly, you should be fine there. Could be coil pack or the crank or cam sensors. Could be a clogged cat but that usually causes issues across the board.

[eyeballs]

Don't have cat. Gap is .042 +/- .001
I always double-check the gapping. The boot for the top wire (cyl#1 IIRC) didn't want to push down far enough but its definately on the plug and I can't see that being an issue. Just didn't want to sit nice and flush like the others.

Are the crank/cam sensors inexpensive? I'll have to do some research on that and how easy it is to replace them. I want to try and eliminate the easiest/cheapest suspects first.

[RotorNutFD3S]

No cat? Well that eliminates that, guess you have a CEL then.

Since this is easy and free, pull plugs and regap to .040. Oddly enough .002 can make a difference.

[eyeballs]

Owner said the car was catless. I looked at the midpipe and saw something with a heatshield and assumed it was a "stealth" resonator/test pipe. There is no CEL. I guess I need to either look under the heatshield or look for a CEL fix. I've been running catless in my Forester for awhile now so I'm used to the smell, I could try a back to back sniffer test too.


Didn't realize .040 was optimal, I think I had read .040 - .043 so I went in the middle. The hesitation did not change when I put the new plugs in. But easy and free = nothing to loose. I'm tempted to try replacing the coil pack and get it over with, I just wish it was a little cheaper. Could be worse though.

[RotorNutFD3S]

.040-.043 is the range listed in most manuals, these cars seem to be happier closer to the .040 gap. What brand plugs are you using?

[mustangtomiata]

Originally Posted by eyeballs

Owner said the car was catless. I looked at the midpipe and saw something with a heatshield and assumed it was a "stealth" resonator/test pipe. There is no CEL. I guess I need to either look under the heatshield or look for a CEL fix. I've been running catless in my Forester for awhile now so I'm used to the smell, I could try a back to back sniffer test too.


Didn't realize .040 was optimal, I think I had read .040 - .043 so I went in the middle. The hesitation did not change when I put the new plugs in. But easy and free = nothing to loose. I'm tempted to try replacing the coil pack and get it over with, I just wish it was a little cheaper. Could be worse though.

If it doesn't have a CEL then the cat is there. My 2000 would have a CEL pop up very very quickly when I ran my catless exhaust. Someone on here probably has a used coil pack which will save you a lot of money. There not too bad to change I did it in a dorm parking lot when I was in college lol

[eyeballs]

The mechanical or resistor fixes don't work on these cars?

Plugs are NGK ZFR5F-11.
I was thinking about trying to find a used coil pack, but if they have short lives wouldn't I be better off with a new one? Of course if the price was right it wouldn't matter as long as it worked.

[mustangtomiata]

I thought the same thing when I bought a used one but say one lasts 100k and you buy one with 50k on it but for a quater of the price that is still a much better deal and a few years of driving.