DanMardik

Hello all,

So for the last month, i've been trying to chase down a severe hesitation problem I've been having on my 97'. First, it started with RPM dropping down to zero for a quick and brief moment when slowly driving away. Then I started noticing a massive bucking or hesitation at WOT during higher RPM's. The RPM tach would go to zero for a brief moment, i would let off the throttle and the car would cruise normally. Anytime I put any kind of WOT in the car, it would hesitate or miss. I first thought it was my Fab9tuning COP set up. So I switched it all back to the stock coil pack set up. Everything seemed fine for about 3-4 days then the issue returned and this time with fury. Anytime I would accelerate anything past 10% throttle it would buck rpm's dropping to zero. If I kept my foot in it, it would just bounce back and forth, bucking hard and accelerating, bucking hard and accelerating once more. Then I noticed that the coil pack bracket was broken and the coil pack was sitting losely on the back of the valve cover. Had the bracket welded and reinstalled. Things seemed normal again. I could go WOT and not have hesitation. But now a new problem. At light throttle whent he car was warm while cruising on the freeway for example at 70mph i can feel the engine hesitating, and softly bucking. When.i go WOT I don't notice this hesitation, only at part throttle cruising. I changed my ignition set up once more and went back to the COP set up I had before and the issue remains. I also noticed that I am getting the RPM drop issue again at WOT. This also returned when I was using the stock coil pack. Because I am running a standalone (Megasquirt) I do not have any CEL's to help diagnose.

List of things I've changed so far.
-New Coil Packs for the COP set up.
-New Spark Plugs
-Fuel Filter

Car details.
1997 Miata 1.8
Supercharged MP62
Megasquirt 1 pnp

Now, i'm thinking it could be the following issues.
-TPS
-CAS
-Fuel Pump
-Injectors
-Engine Coolant Temperature sensor. (I have a coolant reroute kit on the car).

Any help would be greatly appreciated, at this point i'm just at a loss at where to go next with this.

I know this post is a bit long winded so thanks for reading.

pdexta

iTrader: (17)

Do you have a wideband on the car? Is it going lean when bucking/hesitating?

TPS and CLT sensors can be easily eliminated as a potential source by datalogging the issue and reviewing the log. Take a look at injector duty cycles too, are they excessively high at cruise? That would point to a fueling issue (pump, clogged sock, fpr, injectors).

You've pretty well eliminated ignition issues, if you can get some reassurance that you're getting appropriate fuel, then I'd start to suspect a potential cam/crank sensor issue. Check the clearance on the crank sensor?

DanMardik

Thank you for the input. Although I have a Megasquirt I do not have the know how on how to look through data logs and so forth. I just had the car dyno tuned for a few sessions a few years back and that's been about it.
I also do not have a wideband.

soot

I would check the plugs as tach dropping to 0 when you give it beans indicates you're not getting spark, possibly from fouled plugs or blowout, etc. I also strongly recommend getting a wideband in your car, I can't imagine running a forced induction/modified car without one.

Do you have a laptop and a cable to connect your your MS? If so, download Tuner studio and take a log of the hesitation, if you post it up here we can help look for the source of the trouble.

DanMardik

The plugs were all replaced as noted before. Several times. The 0 RPM drop issue would come and go. When I first got rid of the COP set up and went with the stock coil pack. The car ran like a champ for a few days no idea why it came back suddenly. I got new coil packs and went back to the old COP set up and the issue remains so I know it's not ignition related when it comes to those components. I even swapped out the ICM for the COP in case that was acting up. The hesitation at light throttle really starts showing it's ugly head after the car has been warmed fully. Usually about 10 minutes into a freeway drive for example. Once this starts happening, the car will not idle well when I come to a stop light. Stumbling and turning off requiring me to restart the car repeatedly if I don't keep the revs up. (seems to be running on all 4 cylinders however) Some smoke out the exhaust as well indicating a rich condition most likely.
I did purchase a wideband a while back but never got around to installng it. (on the list of things to do)
I should probably take a log of the sitation using Tuner Studio as you mentioned. Just have to get a cable and install it. Was hoping not to get into that.

soot

whoops.

Well the tach is driven off of spark events, hence me pointing my finger there, but there are other things that could cause that. There's a lot of things we can guess at, but pulling the logs will give us a much better place to start looking.

DanMardik

The issue is that the 0 rpm drop hesitation issue is different than the sustained light throttle hesitation (which doesn't cause RPM drops) just gives the feeling like someone is pulling the parking break every few seconds breifly.

Wonder if it Cam Angle Sensor related? Anyone have experience with this?

oreo

I once had an issue where the wiring harness going to the cam angle sensor got damaged and was intermittent.
Finally it failed completely, which made diagnosing it a lot easier.

When it acted up, the tach would read 0.

DanMardik

So today I was datalogging while idling and playing around with Tunerstudio for the first time. Car had been idling for at least 15 minutes and temps were reaching around 200 or so when I had the hesitation again. IWhen the hesitation happened on idle Tunerstudio lost connection for a brief moment before re-connecting. I ran a datalog and it happend again a few moments later. (attached below) I have no idea how to read a log so I hope someone can decipher it for me.. Perhaps it can show something?

DanMardik

Any ideas? Is it possible it has to do with power supply to the ecu?