7.4L vortec running rough

Nope, no issue with the o2 sensors

My 96 had a miss, turned into it backfiring a lot. Turned out the teeth were eat off the distributor. Replaced it and never a problem after that. Tree fell on it and I got rid of it, but still running great for the guy I traded it to.

I was having a similar problem with my 92 7.4 TBI, I ended up replacing the fuel injectors and runs like a kitten again. I replaced one first and it made a huge difference so I went ahead and replaced the second one.

Might be able to get away with just running some fuel injector cleaner through them, try some Seafoam that has helped me in the past.


Good luck

TO ALL OF THE ABOVE!! if you are running the factory multec injectors in your 7.4 trucks go to fiveomotorsports.com and get the bosch replacement injectors!! they are the same as the ford 4.6 mustang injectors. much better pattern of fuel spray. the multecs leak down dripping directly on your spark plugs causing fouling and raw fuel to coat the o2 sensor and killing it. the replacments make a huge difference in these trucks. i do recommend cheching the distributer gears while you are in there as well. good luck!!

Going to a buddy of mine thats a mechanic shop, this week, hope I get it fiqured out. Also changed thermostat. If I do injectors will do Bosh, all I can afford:), can buy AC Delco for sure, high dollar. Going to run a compression check after work today, to be on safe side.

If you find yourself replacing the injectors, don't forget the regulator. Goes bad as well and the time to replace it is when you have the plenum off for injectors, because you can't get to it otherwise. I got one from Standard for like $50 off Summit. Skip the cheapo parts house brands especially Vatozone.

Don't forget to replace the short length of vacuum line too, with some high quality line rated for fuel vapor. If you just use any old vacuum line here chances are it will fail quickly and you'll f'ing hate life taking the intake back apart just to replace a couple inch section of line.

Richard

Going over to my buddies shop this week, will put it on the scanner, and also, clean the injectors with the cleaning agent. One of those cleaners you put in a can with some fule, pop the fuel relay, and run off the can. Try this first. Also ran a compresion check on all cylinders and is running from 145 to 155 psi on all cylinders. Truck has 155,000 miles on it. Did not do a leak down.

155K is enough to start seeing wear in the distributor, so you should check it. Try moving the rotor from side to side. If it won't move, try turning it back and forth a little to where it pops up, then try the side to side movement again. These distributors are notorious for wear in two ways - at the top of the shaft, and the drive gear.

Be careful with the cap screws as it's real easy to break the tabs off the crappy plastic distributor body when you re-install the cap. Chances are they're already cracked anyway. If they break, loop a big zip tie around the middle of the cap to secure it to the distributor base. Works amazingly well on this style of cap, until you get around to replacing the distributor.

Keep in mind if you do find you need to replace the distributor, make TWO very clear marks, distributor body AND rotor position. Try your damndest to install the new one in exactly the same position. This way it will run well enough for you to throw a scanner on it and fine-tune the cam retard, which you do by holding RPM's at least 1,000 for a good reading, and adjust to zero, within +/- 2 degrees is acceptable range.

Richard

Whent to my buddies house yesterday, put on a scanner, no codes, went to past codes got these.
p0327b knock sensor circuit low voltage
p1336a crankshaft postion system variation not learned
p1621c pwer control module memory performance
Also notice a plug that looked like a crank shaft sensor plug not going now where. There is one on the right side hooked up, the exra plug is on the driverside. I do not see a boss in the same place as passenger side. I do notice a plug in fron driver side of block toward the front. Is this where another knock sensor goes?
Also, noticed crank sensor connection, oiley and the plug slipped out when I was messing with it. Died out on way home, had to get a tow($85 dollars 7 miles), then checked fule pressure this moring before work 55psi, then on way to work rembered crankshaft sensor, will buy new and install today.

Crankshaft sensor is at the bottom of the timing cover. There's only one.

There are however two knock sensors on the Vortec 7.4, one on each side of the block, down low about midways back. They both need to be installed, connected, and working. Without that, the PCM assumes "worst case scenario" knock counts and retards timing like 19~20 degrees. You can watch this on the scanner in live data mode, you can disconnect both knock sensors and go for a drive and you'll see high knock counts.

The knock sensors screw into small holes on each side which are just pipe thread, engines that don't have them or don't have both will generally have a square headed pipe plug in the hole.

Richard