Ok so here's the deal. When my car is under load (getting on the freeway) it randomly misses above 4000. It started happening after I tuned up the car (Motorcraft plugs, FRPP 9mm plug wires, Motorcraft cap and rotor, pcv, and fuel filter). I initailly put on a Ford Racing coil, but that killed my tfi module, so I replaced it with an Accel one, then the car would only rev to about 3900 and acted like it was hitting a rev. limiter. Put the old coil back on and it drove normailly for a few days. Then all of a sudden it starts to miss above 4000, like a light sputter/ loss of power, as opposed to the limiter problem before. Mods are Steeda underdrives, timing advanced, Bassani catback and headers, and a ton of suspension stuff. It also lightly surges at idle, but it's always done that. I'm thinking dirty MAF or maybe the stock coil is on its way out. Any other suggestions? I'm gonna clean the MAF tomorrow if time permits, we'll see if that helps. Oh yea, the car is a '90 Lx 5.0 with and AOD automatic. Thanks guys, I'm stumped.
High RPM Miss - need help!
- Thread starter TheTacoWarrior
- Start date
QDRHRSE
New Member
If the problem started right after your tune up you should check all the stuff that you worked on. Check the cap, rotor, wires etc. How did you gap the plugs? It almost sounds like a sparkplug wire is bad. It's too hard to tell based on what we've heard so far but that would be my guess. Under load something is failing. I bet it it's ignition related.
DMAN302
My mom says thanks for the pearl necklace.
QDRHRSE said:
I'm with QDRHRSE. Inspect all the parts that you've recently installed. Also be on the lookout for any vacuum line that you might have dislodged whilel you were working under the hood. If all else checks out and looks good, try closing the plug gap down say... .010 from where it is currently and see if that has an effect. If the problem moves further up the rev range or goes away completely then you'll know that your spark is being blown out. At that point, the coil would be suspect or the input voltage to the coil would be suspect.
Let us know how it turns out!
Black1987Stang
Active Member
i would say something with what uve just done too, i agree with Hissin, ive heard the same problems when some people put in platinum plugs
Thanks for all the advice guys. I used the TFI grease, and I threw out the platinum plugs that were in it and went to Motorcraft non-platinums. I need a fuel pressure gauge to check fuel, but I figure fuel would affect the engine unloaded too. I'm thinking my coil may be weak or my gap too wide, but I hope not. The gap is set to stock spec, but the coil may just be getting blown out. The car has 130,000 and I'm pretty sure its the original coil. It only happens under load, when I free rev it, it won't repeat the problem. I cleaned the MAF today, and that helped, but it didn't affect the high RPM problem, only helped it lower down. Also, I dunno if it's just this damned heat wave we're in or what, but its been running slightly hotter than normal, and it has a 180 thermostat and its running at about 200-210 at cruise on the freeway. Could it be lean? If so, could that be caused by an O2 sensor? I know it doesn't affect WOT, but could it learn a lean curve from a bad O2 and have that affect the WOT settings? Thanks guys. Oh yea the wires are brand new too so I'm thinking they are good. What I need is a fuel pressure gauge and an ignition scope. Oh, and a scantool would be nice too. Haha if only i were rich...
Did you have this same coil on the car for a few days with no issue? A bad coil can definately cause an issue just like you have. Any stang buddies around who can let you borrow their coil for a test run?
Fuel pressure would ideally need to be checked under load - that's when a lack of volume shows up.
You can check codes to see if that gives you a direction to head.
Good luck.
Fuel pressure would ideally need to be checked under load - that's when a lack of volume shows up.
You can check codes to see if that gives you a direction to head.
Good luck.
I'm not sure of the chain of events at this point, but TFI's tend to fail when they get hot, and they often start to cut-out at 4K RPM, or die altogether.
Once the engine cools off, they will sometimes come back to life.
If you take it to the parts store, they can bench test it (have it done repeatedly till the TFI is hot - it's critical temperature is ~257*F).
Good luck.
Once the engine cools off, they will sometimes come back to life.
If you take it to the parts store, they can bench test it (have it done repeatedly till the TFI is hot - it's critical temperature is ~257*F).
Good luck.
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