99 Sub K2500 7.4L Misfire at idle & speed

[saab84]

OK this what I have done so far: Plugs,Wires,cap,rotor,coil and a NTBG MAF.
There was a P0161 code put in new 02 sensor cleared code out (w/MD1052 scan tool)

It is hard to start when it does Black smoke & fuel smell from tail pipe for about 10 to 15sec then clears up, some times it starts right up no smoke.

Fuel psi 60 before start runs at 55 psi, rest psi no lower than 45 after 20 min.

After I did the plugs,cap and rotor the truck ran great for about 20 miles then it started all over again.

Done the intake gasket at 155,000 it has 161,000 on it now.

Gas mileage was 10 in town and 12 Hwy now it's at 8 to 9 Hwy.

I can give reading from the scan tool if you need them.

Any help please

[saab84]

Help Please

[Happy Meal]

I have the same year and model.

You said misfire. But it sounds like it's either getting too much fuel, or it's not burning what it's getting. Have you popped the distributer cap and checked the rotor?
What kind of plugs did you put in?

[saab84]

New cap & rotor

Put A/C R44LTSM6 in first then scanned and there was a misfire on #2,3&8
Then put in NGK TR55IX Iridium plugs with no change.

[Happy Meal]

Might want to check those plugs. NAPA does not show those numbers for the 7.4
Mine had AC 41933. I've been told to only use them.

Also. I've seen guys either not put the rotor on properly or they come off. Anyway, when that happens the car runs like it's missing on a couple cylinders. Also chews the cap up pretty good inside.

[saab84]

The 41933 crosses over to the NGK# the NGK and the a/c plugs are the same.
The copper cores worked ok but the misfire was still there.

[777stickman]

Pull the cap again and check for any rotational play with the rotor on the dist shaft. Hold down pressure on the rotor and gently turn the rotor back and forth. No rotational play is allowed. Also check for any side to side play.

Recheck base timing (cam retard/cam offset). Needs to be 0 +/- 2degs @ greater than 1000 rpm.

[saab84]

Pulling top of intake off and testing injectors & fuel regulator and Dist shaft.

[Elbert]

A/C plugs for GM vehicles. No check engine codes now?

[saab84]

Originally Posted by Elbert

A/C plugs for GM vehicles. No check engine codes now?

Never have had any check engine codes, the only code I had was the one 02 sen. code & a ABS code

[grumpy5]

Did you find anything with the injectors? Leaking? Stay with Delco plugs. I tried bosch several years ago and induced a rough idle problem.

[saab84]

Had new A/C plugs in still had same rough running at idle and speed.

Pulled top of intake off had a strong fuel smell in lower intake.
The truck has been sitting for two days only turned key on to take out of gear so I could push it back. (fuel pump comes on for about 10 sec. with key on.)

Once had top intake off turn key on to check if any of the injectors where leaking no fuel came out.
Ohm all the injectors they where 13.5 to 13.3

Checked Dist as 777stickman said and when holding down on rotor there is a very small amount of play. no play any where else.

[saab84]

Putting clean rags under each injector let it set over night and see if any of the rags get wet with fuel.

[777stickman]

I see that you had a very small amount of rotational play on the rotor. The manual says none is allowed. Lots of folks have fixed similar issues with a new dist or gear.

Stay with Delco stuff for the cap, rotor, wires & plugs.

More ?'s. What do the plug's look like when you change 'em out? Do they have a lot of soot on 'em (rich) or just a good tan color? Seems that if it's running as rich as you say that the O2's would set a code.

One other thing. My '98 K2500 7.4 had misses when I first got it used with 40K. Had to do the intake gaskets and found 2-3 injector wires rubbed bare under the upper intake cover. Not sure if fixing that or the gaskets cured it but it's been good since, now @ 155k.

[saab84]

Injector's are not leaking.
Checked the vacuum hose on fuel regulator it had a small amount of fuel in it. Replaced the fuel regulator, starting better will take for a long test drive tomorrow will post results.