Stumped

[turkeyhunter7880]

Hello. First time posting. Hopefully someone will be able to she's some light on this p.o.s.. I have a 96 Tahoe. I can only accelerate to about 1/3 if the throttle (slowly) before it falls flat on its face. U changed the distributor, cap and rotor. I have a cheap little scanner that's saying my timing is around -16.5 upon acceleration it jumps to about-25 deg. Any help would be greatly appreciated.

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[drakon543]

your truck has electronic timing advance you will see it jump all over. the timing is set to 0 and i think it gives you a +/- 1 or 2 degrees if its off you will have a code that specifically states the timing is off. if you dont have a code for distributor timing off your timing is fine. it could possibly be a faulty tps they are also a known problem. a tps is going to either fail completely or have dead spots. if you hit the dead spots as far as the ecu is concerned you let off the peddle so its cutting the fuel. let us know if you have any check engine codes stored.

 

[liquify33]

Those numbers should be positive I believe, +24 degrees roughly at wide open throttle.

There are cheap scanner/app combos that will tell you the cam/crank separation to dial the distributor in.

 

[turkeyhunter7880]

Yeah I don't understand why the timing is so far retarded.

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[turkeyhunter7880]

No codes right now. Every once and a while it throws a lean code. I should add that fuel pressure tested good and it idles fine. I bought the truck this way. Idk what the previous owner did to it. Is it possible they pulled the dist. And have it a tooth off. Also I had the tps checked at the parts store. Supposedly it tested good.

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[drakon543]

p1345 is the code telling you the timing is too far off and its 2 degrees is the tolerance you get. a scan tool with a normal timing reader on it wont work. it needs to specifically read timing retard not the regular timing. again tho if p1345 isn't popping up your timing is fine. if its off it will pop that code within seconds of starting the engine. been a bit since i had to mess with my 97 so i went and looked it up. 96-99 had this setup and a handful of 2000 also had it if they still had the 5.7

 

[drakon543]

without p1345 im definitely leaning towards your tps throttle position sensor. if you have a multimeter its easy to test. set it to ohm connect it to the plug and slowly turn the throttle by hand. it should have a slow gradual change in the ohm readings. if it hits a spot where it starts jumping around or suddenly changes drastically its your tps. a faulty tps wont always pop a code.

 

[liquify33]

I ran my distributor at +4 for weeks without a code. And my above numbers were off. +22 is idle, it’s in the 30s with throttle.
1st pic is “timing” at idle


2nd pic shows the cam offset reading (CMP RETARD)
This reading is only accurate over 1000 RPM

 

[drakon543]

at +4 your only going to pop a code if you hit the spot just right its not out enough to effect operation. if timing is off enough to actually effect how the engine is running it will pop p1345. if his timing is off enough where he cant even give it much throttle he would be popping a code. i ran my 97 a whole tooth off for a week and ran perfectly but would give me a the p1345 code occasionally. like i said if it was the timing and its off enough to actually effect how its running it would have a code.
hmm another thought just hit me also potential fuel related issue. if you dont have the fuel pressure needed to keep the engine going properly past your stated 1/3 pedal could also be a potential.

 

[liquify33]

The “timing” is programmed into the computer and requires a tuner to edit. The CMP offset measures how well the distributor was installed. As I understand it, the computer tells the coil/ICM when to fire, the distributor is only to get the spark to the correct cylinder.
With the timing mark lined up, the rotor should point one of 2 places: toward the passenger seat (#6 maybe?) or toward the driver tire at TDC #1.

If you’re running at all and not idling violently then you’re close. There is good bit of adjustment in the distributor degree range.

A 1/2” distributor wrench, scanner and $20 in apps or let a shop correct it. If I can do it, anyone can.Just remember to check CMP over 1,000 RPM