89 SC won't run above 1500rpm

sgolenski

Registered User
89 SC has run great (within reason) for the past 34 years. Last summer the cam sensor finally died. I replaced it and drove it for a few weeks until the clutch master cylinder took a dump. about 2 days after that, I was on my way to the grocery store (maybe a mile from home) and out of the blue it runs like crap at about 1500rpm. Now when I say "crap", I mean it pops, bucks and has no power (obviously). It happens under load, in neutral, whenever. I also notice that the tach dances a bit when this is happening, not as bad as when the cam sensor went but it does dance. Is this the crank sensor finally taking a shit? (I have a new one on the shelf). Am I looking for something else? Ideas? Car is unmolested, bone stock.
Thanks!

Scott
 
Tach dancing is usually the DIS module or the cam sensor(which I know you already replaced),but it
could've went bad.
 
is this the crank sensor

Is the upshift light on when cranking to start?

Are you able to pull codes?

Are you able to attach a fuel pressure gauge to the fuel rail and monitor fuel pressure?
 
Doug H - DIS was replaced a few years back. I have a Motorcraft Cam senor on the shelf (NOS). I never considered the DIS. Easy swap though.

KMT - As far as I know, the upshift light is not on when I crank it. Although it doesn't crank long before it starts so I haven't paid attention. I personally don't have the means to pull codes nor can I check fuel pressure. I do have a trustworthy shop that I've been taking my cars to for years.
 
Since the DIS was mentioned, where do I find one? Super Coupe Performance? Seems to be about as available as the crank sensor.
 
Do you have another DIS or just the cam sensor? Try what ever you have, as you said both are easy swap's.
If one doesn't work then try the other. If still no improvement the next thing would be pick up a code reader
& see what codes if any are set. I assume if it running that crappy, the light is on & some code(s) will be stored.

It sure sounds like its getting intermittent or corrupt signal from cam sensor though
 
Napa # TP56 Standard Motor Products # LX-242 Motorcraft # DY655
Check with your local supplier to confirm though. I've had good success getting the LX-242
 
My 91 SC wouldn't even run on the DIS module sold by O'Reilly Auto Parts, but the Ford F1SF-12A297-BA or Motorcraft DY-958
worked great.
 
If you're going to fire the parts cannon at it without having codes to support, you might as well start w/the cheapest low hanging fruit, which is the readily available and decently priced cam sensor. Be sure to keep receipts in case a purchased part gets pricey and doesn't solve the issue.

As well, keep in mind that while a given part can fail outright, sometimes just handling a connector off/on can clean the contacts enuf to make it appear like the old part was the problem, when in fact all that was needed were more reliable current/signal/ground paths. Checking wiring harnesses/electrical connections for corrosion and damage is a no-cost tactic that again, in the absence of methodical troubleshooting that includes pulling codes, makes more sense than simply blasting parts at the problem.
 
Check for cam sensor stalk play. I actually had a near catastrophic failure with the timing chain tensioners bad and chain and gears about to let go and also grinded away at the cam stalk and cam gear aswell, my car is not stock however. But cam codes were present, sensor was fine it was the metal stuff failing. Just something to think when diagnosing. I used a borescope after took the synchronizer out and saw wear on its gear.
 
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