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Speed Density/Carb/SSP section This section is for the Speed Density or Carb vehicles, as well as Special Service Package 'Stangs

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Old 01-04-2014, 05:25 AM   #1
Dachipsta
 
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Default Cutting in/out while cruising.......opinions please.

Hey folks, this is something that Ive been dealing with now off and on intermittently for a few months. Seemed like I had it licked when I pulled the distributor and replaced the PIP, changed TFI and also swapped coils with another one(not new) that I had laying around. I had this happen a while back due to the ignition switch falling apart but that had been accompanied by accessories like the hvac blower shutting off for no reason. That was fixed and this time isnt switch related.

Reason I'm asking opinions this time is that I was reading a thread on another forum and someone mentioned a similar issue caused by having the primary power lead from the 3G alt. running near the TFI module. I guess during periods of high loads...ie. elect fan running, a/c, head/fog lights...ect would induce interference into the ignition causing misfires/cutting in and out and such. A while back I replace my radiator and my power lead for the alt runs under the radiator support and over to its fuse and to the battery. In my infinite wisdom, I decided to thread it across the front of the engine, behind the a/c comp, under dizzy and over to the alt. covered w/ black plastic wireloom stuff. Now that I think back, the intermittent ignition problems seemed to have started right after that. I did recently upgrade my cheezy sorenson TFI with an Accel from NPD along with an Accel Coil and new FRPP wires. I am planning on relocating the alt wire back to the radiator support today so I can see if it makes any difference. Of course, if it does I prolly wont know if it was that or the generic TFI or shi**y coil that was in there.......lol.

Anywhoo, just curious if anyone has experienced anything similar. FWIW, it also is stumbling a bit in the upper RPMS when I put my toe in the radiator. That may be fuel related as the fuel pump is now 8-10 years old and I cant remember when the fuel filter was changed last which is getting done today along with new back brakes. Thanks for any ideas......l8r
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Old 01-04-2014, 08:37 AM   #2
dawson1112
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I think the fuel filter change is a good start.

How ever there is a difference in fuel related and spark related power loss. Generally spark related missing is a very sharp cut out like a quick stutter like eh eh eh eh , while fuel related missing is a more boggy and drug out like ehhhhhhhh as it falls off . ( q sound effects lol ) How ever a failing fuel pump that is intermittently cutting off and on quickly may be a quick stutter as well.

I suggest getting a fuel pressure gauge on it that you can view while driving it and watch the fuel pressure as you accelerate quickly, If it starts to fall off rapidly as you jump on the throttle that could very well be your trouble. It should stay between 32 (min) and up to 42 (max) more likely 34-38psi , but if it drops below 32 psi the injectors will not function properly.
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Old 01-04-2014, 06:40 PM   #3
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Thanks for the reply. The upper RPM stumble was in fact the fuel filter. It now pulls strong thru the entire rev range. The fuel pres. gauge I have under the hood is ok for baseline readings and such but one like you are suggesting would be nice. It would make solving these issues a bit easier thats for sure.

I havent had enough time behind the wheel the past few days to be able to tell if the other lil' gremlin is still around. I havent completely rerouted the power lead for the alt. but I did move it from where it was lying right next to the TFI module and got it secured a few inches away so we'll see what that does. This stuff really irks me because this car has always been good for if I wanna go make a 400 mile trip somewhere, I used to could just jump in and go. I bought it in 97 and it had only 48K on its clock and it doesnt seem like its as old as it is. Its always been my daily and I am gonna hate it if I have to retire it because of BS stupid intermittent stuff......grrr.
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Old 01-06-2014, 03:22 AM   #4
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Well, I found the culprit finally and it looks as though I have nothing to blame but my own idiocy. I was checking my base timing yesterday as I had just replaced the Sorensen TFI with one of the Accel pieces. I had just finished tightening down the lock bolt for the dist. and was pulling my swivel/socket out from behind the wiring and the engine stumbled and tried to die and smoothed back out. Turns out it was a miffed connection with the TFI plug wiring. I changed out my WP a few years ago and when pulling one of the bolts, my extention had been lying up against the TFI plug and shattered it. I had to get a new plug and it comes with a pigtail, HS tubing and whatnot to splice it into the existing wiring. I cut open each of the connections and found one that was just together in the HS w/ no solder!.....lol. All the rest were fine but I guess I got distracted by something at the time and didnt solder one of them up.......Dammit man. Oh well, I am happy that my lil gremlin is gone and now I can get on with my life. Good lesson learned on this one and I'm always bitchin that I'd rather do my work myself inistead of taking it to some HACK......hahaha, now thats funny.....: P
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Old 03-09-2014, 10:09 AM   #5
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I have a 90 gt, trick flow heads, 30 lbs injectors, 70 mm. The engine runs fine on the low end. The engine dies at wide open throttle. Fuel pressure regulator is 36 lbs, 40 lbs with vacuum unhooked. I ran the gauge inside the car, when I drove it hard the fuel pressure dropped to 25 lbs and took a while to build back up. Fuel pump is 6 months old, just dropped the fuel tank to check the strainer. Fuel filter is an in line Russell. KOEO codes are just smog stuff.
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Old 03-15-2014, 11:44 AM   #6
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Quote:
Originally Posted by Charlieg3 View Post
I have a 90 gt, trick flow heads, 30 lbs injectors, 70 mm. The engine runs fine on the low end. The engine dies at wide open throttle. Fuel pressure regulator is 36 lbs, 40 lbs with vacuum unhooked. I ran the gauge inside the car, when I drove it hard the fuel pressure dropped to 25 lbs and took a while to build back up. Fuel pump is 6 months old, just dropped the fuel tank to check the strainer. Fuel filter is an in line Russell. KOEO codes are just smog stuff.
What kind of fuel pump you running?

I don't think the stock fuel pumps are good for 30lb injectors, I have a walboro 255lph running 30lb injectors. My fuel pressure never drops to less than 32 .
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Old 03-16-2014, 09:17 PM   #7
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The fuel pump is a walbro 255lph that I installed a year ago. I realize it could have gone bad. I am trying to figure out how you deter,ine if it is the fuel pump or the fuel pressure regulator.
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Old 03-16-2014, 10:23 PM   #8
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Quote:
Originally Posted by Charlieg3 View Post
The fuel pump is a walbro 255lph that I installed a year ago. I realize it could have gone bad. I am trying to figure out how you deter,ine if it is the fuel pump or the fuel pressure regulator.
Since you know the regulator is functioning as it should at idle with the vacuum unhooked ( meaning it goes up like it should ) then I would suspect the pump, because at wot it is almost like taking the vacuum line off it should go up a little or stay about even. If the injectors are spraying fuel faster than the pump can maintain the pressure then you have a blockage in the filter , sock or the pump is going out.

I mean the pressure might see a small drop if you hit WOT fast but the pump should be able to bring it right back in no time. But to drop to 25 and take a long time to recover is not right.
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Old 03-17-2014, 07:07 AM   #9
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Makes sense, I have read several posts where new fuel pumps went bad. Thanks.
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Old 04-22-2014, 07:07 AM   #10
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Turns out my fuel pump was bad, replaced the pump and now the car runs great.
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Old 04-22-2014, 07:07 AM
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