1999 Tahoe bad misfire

[1loudhoe]

soooo, i have been dumping money in my hoe non stop lately to try and fix this problem and nothing has worked, so far i have done the following: cold air intake, dual exhaust (first 2 things i do to every vehicle), plugs, wires, coil, cap and rotor, switched over my fuel injection from SCPI to MPI, fuel pump, fuel filter, throttle position sensor, 195 thermostat. After ALL that it still stumbles and did i mention i am getting 7-8 mpg WTF!!!! let me explain, when i am driving at a constant speed it is real noticeable like on the freeway but if i am romping around in town its not that noticeable also if i drive at 45mph then drop it down a gear and the rpms jump up it gets real bad and starts to spit and sputter and back fire. PLEASE HELP ME!!!! i am about to put a rag in the gas tank and watch the fire works because i am so frustrated

 

[lesterl]

Fuel pressure?

Who did the MPFI conversion? Are you shure the injectors were installed properly?
http://www.tahoeforum.com/showthread.php?t=528552

 

[1loudhoe]

The fuel pressure WAS all over the place that is why I did the MPFI upgrade and fuel pump (I am ASE certified and have been managing a shop for almost 5 years) I haven't checked pressure again since I just know it is still missing, the scanner says misfire on all 8 cylinders (I have replaced plugs, wires, cap and rotor, coil) still did nothing to fix the problem. From what I have been reading I should check the distributer and the crank position sensor??

 

[lesterl]

Checking play in dist is good, drive gears tend to wear. How was the dist timing set after the MPFI upgrade?

What value does the CTS ohm out at?

 

[1loudhoe]

There is some play in the distributor (1/4 inch each way) I was not aware that something had to be set after installing MPFI please enlighten me? CTS??

 

[lesterl]

Yup gotta set the Dist with a Tech 2 and perform a "CASE RELEARN" after restabbing the distributor. They are very touchy, Just did the LIM on my 98 Sierra a while back and I didnt set mine with the Tech 2, but there is a logic probe way to set it also..... and I had time to mess with it a while....

 

[1loudhoe]

But I did not remove my distributor. Do I still need to do this?

 

[ma87k5]

If it didn't come up with a code about timing then you are fine. P1345. You said you didn't remove the distributor. Then you are good. Case relearn? Nope A scan tool is needed to set the timing after removing the distributor if you didn't put it back in the exact same position it was in. Double check all your connections and spark plug wires. Take your time and don't rush.

 

[lesterl]

If you just bought it the Previous Owner may have jacked it up.... I did not get the p1345 on mine, still dont have the code, never set it with a scantool, used another method. It doesnt take too much to throw the timing off........ Could be the LIM has been done and the dist was not relearned then....

CTS is Coolant Temp Sensor, it should be near the water neck where the thermostat is, the one in the drivers head is for the dash guage, you want the water neck one as it reports to the PCM, this sensor being bad could report that the coolant is like below 0 and run the engine pig rich....

 

[1loudhoe]

how common is it for the CTS to go bad??

 

[lesterl]

It happens, just replaced a temp sender in an oven today.... You can just pull the plug off of it and ohm the 2 pins out, report back what ohms the sensor was and temp the block was.....

 

[1loudhoe]

with the ohm meter set on 1000's it read 225 ohm's @ 195 degrees

 

[lesterl]

225000 ohms = VERRRY COOOLLLLDDDDDDD or is it actually 225 ohms, because that would be close to accurate...

 

[2000tahoez71]

Most meters when set to 1K read out in single ohms, so 225 is actually 225 not 225K. I've got to do the LIM gaskets next weekend, along with the MPFI conversoin, new cats and all O2 sensors. I don't have a tech 2 tool, and plan to reference mark everything on the distributor to get it as close as possible. Should I throw a new dist. gear in there while I'm at it? What's the logic method of setting cam retard.

 

[lesterl]

Is the gear worn? I had 287k on mine and I replaced it as it had some slop, helps keep timing more accurate......

Logic probe method of setting cam retard->
http://www.askamechanic.info/askamech2/content/view/49/47/

I actually just adjusted mine and adjusted untill I got it where it turned the light off.

 

[1loudhoe]

CASE CLOSED!!!!!!!!! there are alot of thing i found to be part of the problem in this situation MOST of witch were pointed out buy you guys that commented on this thread so first and for most THANK YOU...ok on with the problems i found 1. CHINES PIECE OF **** PARTS i.e cap, rotor, distributor, plugs, wires, coil, ALL EXCEL brand. NEVER will i put anything but american made/AC delco parts in my truck. 2 of the ends on the wires where broke, the center contact on the rotor was snapped off and laying in the bottom of the distributor, all the contacts on the cap were lose, the gear on the bottom of the distributor was wore almost in half (stock) 2. wires that went to my cam position sensor where laying on the manifold and melted (grounding out) 3. O2 censors B1S1 was bad 4. cylinder 3 had low compression.

 

[lesterl]

Nice....