5.0 mustang low RPM miss

Jeff Stockham · 12-30-2006, 10:45 AM

I have a 1990 5.0 Mustang that has developed a high-load, low-RPM miss. The miss is most noticable at WOT below 2000 RPM and goes away with increasing RPM. My guess is that it is ignition related. I have replaced the plugs, wires, distributor cap, rotor, coil, and the TFI module with no success. It has slowly gotten worse over time.

Any suggestions would be appreciated.

Thanks,

Jeff

Mr 5 0 · 12-30-2006, 02:32 PM

This is a tech question and should be moved to the Windsor Power forum.

Capri306 · 12-30-2006, 06:29 PM

No problemo.

Mebbe you're leaning out. Is it just when the engine is at operating temperature, or all the time? Have you tested the MAF sensor?

Jeff Stockham · 12-31-2006, 10:48 PM

The miss appears to be independent of engine temperature. The mass airflow sensor was replaced a couple of years ago. It's the most noticable in 5th gear.

USMC302 · 01-08-2007, 12:54 PM

Sounds like timing. What's it set at right now?

Coupe50h · 01-08-2007, 10:17 PM

Any mods?
If you have aftermarket rockers, adjustment could be out, you could be losing compression? just a guess.

Also, sounds ignition related, but it could be a weak fuel pump, you need to be sure your getting fuel pressure.
And that you dont have a defected coil, even if it's new.
Check engine grounds, and see if you can run a code scanner, and pull codes. could be a number of things, clean the maf, i dont care if it's new, and make sure all injectors are squirting.
good luck..

Unit 5302 · 01-09-2007, 07:07 PM

Is it an audible misfire (backfire?) Does it clear itself out after a few pops?

Either one of those scenarios sound you could have a broken or failing fuel injector.

12-30-2006, 10:45 AM	#1
Jeff Stockham Registered Member Join Date: Dec 2006 Posts: 2	5.0 mustang low RPM miss I have a 1990 5.0 Mustang that has developed a high-load, low-RPM miss. The miss is most noticable at WOT below 2000 RPM and goes away with increasing RPM. My guess is that it is ignition related. I have replaced the plugs, wires, distributor cap, rotor, coil, and the TFI module with no success. It has slowly gotten worse over time. Any suggestions would be appreciated. Thanks, Jeff

12-30-2006, 02:32 PM	#2
Mr 5 0 Conservative Individualist Join Date: May 1997 Location: Wherever I need to be Posts: 7,487	Re: 5.0 mustang low RPM miss This is a tech question and should be moved to the Windsor Power forum. __________________ 5.0 Mustang Owner 1990 - 2005

12-30-2006, 06:29 PM	#3
Capri306 Moderator Join Date: Sep 1998 Location: Grand Rapids, Michigan, USA Posts: 1,001	Re: 5.0 mustang low RPM miss No problemo. Mebbe you're leaning out. Is it just when the engine is at operating temperature, or all the time? Have you tested the MAF sensor? __________________ Capri306, Moderator The Mustang Works Online 1979 Mercury Capri 1987 5.0L Mustang LX Notchback 1993 5.8L Eddie Bauer Bronco

12-31-2006, 10:48 PM	#4
Jeff Stockham Registered Member Join Date: Dec 2006 Posts: 2	Re: 5.0 mustang low RPM miss The miss appears to be independent of engine temperature. The mass airflow sensor was replaced a couple of years ago. It's the most noticable in 5th gear.

01-08-2007, 12:54 PM	#5
USMC302 Registered Member Join Date: Apr 2001 Location: Gallatin, Tn Posts: 1,326	Re: 5.0 mustang low RPM miss Sounds like timing. What's it set at right now? __________________

01-08-2007, 10:17 PM	#6
Coupe50h Registered Member Join Date: Aug 2002 Location: SanAntonio, Tx Posts: 957	Re: 5.0 mustang low RPM miss Any mods? If you have aftermarket rockers, adjustment could be out, you could be losing compression? just a guess. Also, sounds ignition related, but it could be a weak fuel pump, you need to be sure your getting fuel pressure. And that you dont have a defected coil, even if it's new. Check engine grounds, and see if you can run a code scanner, and pull codes. could be a number of things, clean the maf, i dont care if it's new, and make sure all injectors are squirting. good luck.. __________________ X-Texas highway patrol ssp 1990 coupe - exploder Gt-40 iron heads, Explorer intake, 19 lber's. E-cam. crane 1.7 rollers. 190fp. 75mm maf. 65mm tb, tubular subframe connectors, mac cai, Asp crank pulley, T-5, king cobra clutch, flowtech 1-5/8 unequals, mac X-pipe Frpp driveshaft, lakewood Lca's. race weight 3,160 12.69 @ 107.35, 1.71 60' 26x8.5 drag's 3.90 gear 13.20 @ 106.91 - 235/60/15 firestones 2.3 60' 3.27 gear

01-09-2007, 07:07 PM	#7
Unit 5302 Registered Member Join Date: May 1999 Posts: 5,246	Re: 5.0 mustang low RPM miss Is it an audible misfire (backfire?) Does it clear itself out after a few pops? Either one of those scenarios sound you could have a broken or failing fuel injector.

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