Car stumbles at higher RPM's?

rabidscoobie

10 Year Member
Jun 21, 2007
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College Station,TX
Have a 2004 Mach 1 stock.Roughly just at 100k miles.

Recently if I floor it in 2nd or 3rd gears and hit roughly 4k+ RPM's the motor bogs almost like no fuel but I can hear small pop sound from under the front floor pans, think more so on passenger side. I have no CEL or codes and other than that car idles fine and drives fine until I get on it.

Any Ideas were to look?
In a bit Im gonna check fuel pressure and replace the fuel filter then test pressure again.
Im thinking either bad filter, failing pump or possibly clogged cats.
Anything else I can test or look for before throwing money at it.
 
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kiddiccarus

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Watching: Having this same issue between 1st and 2nd in my 02 3.8 engine same symptoms. I have messed with the idle some thinking it may help but It made it worse so I had to back it down to almost 1k.

Does your run smoothly if you just shift normally and drive but only does this when you are getting on it????
 

rabidscoobie

10 Year Member
Jun 21, 2007
609
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College Station,TX
Watching: Having this same issue between 1st and 2nd in my 02 3.8 engine same symptoms. I have messed with the idle some thinking it may help but It made it worse so I had to back it down to almost 1k.

Does your run smoothly if you just shift normally and drive but only does this when you are getting on it????

Yes it will idle and drive smooth under normal loads, if I floor it then between 4-5k rpms it falls flat.
Replaced the fuel filter of which was pretty bad and replaced a dry vac line but didnt fix, still trouble shooting.

Checked fuel pressure and reads 30 psi at idle, goes up as I rev.
Coils are properly seated and all are getting 12v+, still looking into them but I think coils are good.

I also forgot to mention.
The first instance I noticed something was wrong was a couple nights ago I floored it then it fell flat but didnt recover, it just kept bogging and stuttered as if it were out of gas until it died. I cycled the key a fey times then tried to start and fired right up no issues. Hasnt died but that one time.
 

kiddiccarus

The first widely accepted Tranny
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I have:

Checked my pressure and its good all the way through to 5500
Checked my Plugs and Wired (New Anyways) for seating.
I am getting 12v+ all through also.

I am going to replace my fuel filter while doing the Torque box kit.

I believe that we have the same problem. I just filled the tank last night and added a can of seafoam. I am not thinking that this will fix it though. Some common denominator is happening with the cars that we may be overlooking.
 

rabidscoobie

10 Year Member
Jun 21, 2007
609
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College Station,TX
I have:

Checked my pressure and its good all the way through to 5500
Checked my Plugs and Wired (New Anyways) for seating.
I am getting 12v+ all through also.

I am going to replace my fuel filter while doing the Torque box kit.

I believe that we have the same problem. I just filled the tank last night and added a can of seafoam. I am not thinking that this will fix it though. Some common denominator is happening with the cars that we may be overlooking.
Im leaning towards possibly cats or fuel pump. Being my luck it would be fuel pump since I just filled up the tank and maybe used 10 miles it...lol.
Im on my way to buy another IR thermometer gun since mine took a dump to test the before and after cats temp.

Also if anyone here can tell me how to correctly check the COP's other than making sure they are getting power Im all ears.
I did the pull one off at a time test, yes I know your not suppose to but its the only way I know. All 8 seem to be working.
 

Noobz347

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I would guess spark or air:


Look for a cracked [something or other] in the inlet tract. A hard piece of plastic or hose or whatever... Look underneath them all. Inspect closely.

Check coil saturation at RPM. Make sure voltage is [not] dropping at the coil when you're hard on it and check wires for any arching.

After that is the point that I'd start looking at fuel system.
 

rabidscoobie

10 Year Member
Jun 21, 2007
609
10
48
College Station,TX
I would guess spark or air:


Look for a cracked [something or other] in the inlet tract. A hard piece of plastic or hose or whatever... Look underneath them all. Inspect closely.

Check coil saturation at RPM. Make sure voltage is [not] dropping at the coil when you're hard on it and check wires for any arching.

After that is the point that I'd start looking at fuel system.
The ach has the Cop so no wires, boots look good.
Ive checked vac lines and most all looked good, replaced the long one thats just under IAC and goes into the fender on pass side to a kind of half soup can looking thing.

As for coil sat, Im not familiar with that or know how.

Ive had a couple people mentioning to check the irmc plates and crank sensor.
also the temps for the cats are kind of all over the place but not sure how they should read.

THis what I got for the temps:
Pass side.
Before 1st near motor 300
Between 2 cats 430
After 2nd 350
But... small cat 1st on front part is 150 back part is 220
2nd cat front 370 back is 265

Driver
Before small 400
Between cats 415
After 2nd 305
Small on front 270 back 445
2nd front 298 back 265

Those temps are kinda all over. Does this look like possible problem im having
 

rabidscoobie

10 Year Member
Jun 21, 2007
609
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College Station,TX
OK I got it fixed, running strong now and you can feel the pull when it hits 5k now.
Problem was the plug on the crank sensor somehow came loose, not off but wasnt making full connection. The lock on the plug isnt broken so I have no clue how that happened. Last time I was even under that side was to replace the AC comp and that was 3 years ago.
I did do motor mounts last summer but no reason to disconnect that plug.
 

kiddiccarus

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Dec 24, 2003
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Had some free time at the shop so I got my car up on the alignment rack and found that I have 1/8 play in the connection to the Crank Sensor. I grabbed a replacement pigtail at AutoZone on the way home and will install it tomorrow. I did push the existing connector in all the way and it is a noticable difference.

I think I used the pigtail from the 95 on it. I will test the connector that is for the 02 before I splice it in for fitment. While it is up I will replace the fuel filter and the pigtail for the AC compressor also. Might as well
 

rabidscoobie

10 Year Member
Jun 21, 2007
609
10
48
College Station,TX
Had some free time at the shop so I got my car up on the alignment rack and found that I have 1/8 play in the connection to the Crank Sensor. I grabbed a replacement pigtail at AutoZone on the way home and will install it tomorrow. I did push the existing connector in all the way and it is a noticable difference.

I think I used the pigtail from the 95 on it. I will test the connector that is for the 02 before I splice it in for fitment. While it is up I will replace the fuel filter and the pigtail for the AC compressor also. Might as well
Sounds like you had the same issue then. Hope it all works.
 

kiddiccarus

The first widely accepted Tranny
15 Year Member
Dec 24, 2003
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Swapped that Crank Sensor Pigtail today. I test fit it out of the box and it was a bitch to get back off. I must have used the 95 pigtail that was on the original harness and that one seems to be too short to let the lock click. Once I got this one back off and spliced it in, I made sure the lock clicked.

The 95 pigtail and the 02 Pigtail are different colors on the inside also. So that was a give away that I had the wrong one on. So, Just because a pig tail "fits" and has the same amount of wires on it, it does not mean that it is the correct one for the job.

I also swapped the fuel filter and the pigtail for the A/C Compressor while I had it in the air.


Drives Smooth now. So, I would like to thank you and your Mach 1 for having this issue which led to helping me fix mine.
 

rabidscoobie

10 Year Member
Jun 21, 2007
609
10
48
College Station,TX
Swapped that Crank Sensor Pigtail today. I test fit it out of the box and it was a bitch to get back off. I must have used the 95 pigtail that was on the original harness and that one seems to be too short to let the lock click. Once I got this one back off and spliced it in, I made sure the lock clicked.

The 95 pigtail and the 02 Pigtail are different colors on the inside also. So that was a give away that I had the wrong one on. So, Just because a pig tail "fits" and has the same amount of wires on it, it does not mean that it is the correct one for the job.

I also swapped the fuel filter and the pigtail for the A/C Compressor while I had it in the air.


Drives Smooth now. So, I would like to thank you and your Mach 1 for having this issue which led to helping me fix mine.
No problem...lol
Glad it worked for you too.
 
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