Poor acceleration, no 'top speed' 92 K1500

[shibbershabber]

Ongoing saga of misery and dispair... (6 months later) 92 K1500

Okay, I have a 1992 K1500 suburban 5.7 TBI 150k mi.

I have very poor acceleration... I know my truck is a slug, but this thing cant seem to get out of its own way!

Also noticed that it is very hard to get going over 60-65mph



Things Ive already done:

I replaced the fuel pump/sender assembly <1k mi ago
Also did the fuel filter at the same time.

I replaced the wire harnesses to the fuel injectors because they looked burned

I also rebuilt the throttle body and replaced the injectors AND while I was in there I did the EGR valve... just to do it.

I replaced the TPS (was told it could be the cause of my no OD problem)


Other known problems... not sure if they relate to my poor performance

no OD (replaced TPS, had Cottman adjust the TV cable)
trans has late 2-3 shift and is sometimes hard shifting 1-2

Burning a little oil sometimes...

low voltage, possible bad battery or alternator... havent checked yet

Accelerator pedal seems tight? cant see where it could be binding at all, but it requires a lot more pressue than any other vehicle Ive owned including a 93 K2500 6.5, and a 96 3500 box van (5.7 vortec)

The effing box van gets going better than my Sub... wtf?



Thanks!

 

[Enginebuilder]

I also rebuilt the throttle body

Accelerator pedal seems tight?

I believe that these two are related. To diagnose, disconnect the throttle cable from the throttle body, and then attempt to move the throttle plate; if no undue resistance, with the throttle cable still disconnected, move the throttle pedal- there should be nearly zero resistance. Chances are, some springs are binding up, or mis-routed, and this is causing your hard throttle pedal issue.

Before you go disconnecting anything, take some pictures of your throttle body and associated linkages and post 'em up- we can compare against ours, and identify any potential issues that way...

I don't like the fact that you've got issues with the transmission *and* engine at the same time. A problem with one could mimic or mask problems with the other. Especially the transmission- a properly running engine is going to *seem* like it can't get out of it's own way when 1/2 of its output is wasted by a transmission with issues. I would suggest that you get the transmission checked out by a proper specialist, who can test the line pressures through the range of gears.

If that doesn't point you toward serious issues (cross fingers) I would follow up with a compression, leak-down, and vacuum tests. Post the results of those, and we can probably help point you in the right direction.

 

[TylerZ281500]

honestly take off your spark plug wires one by one. you mentioned the wiring harness looked burnt. any oil soaking or odd heating will kill a spark plug wire and you may never expect it. same thing happened to me on my old truck and it was plugs and wires. not saying it is on yours but its worth it to check.

 

[shibbershabber]

The spark plug wires, cap/rotor, plugs are less than 2k miles old. The previous owner had replaced them in an attempt to resolve the issue that turned out to be a fuel pump.

Still not sure what the deal was with the burnt injector harnesses was... the new ones are holding up well so far. (the wires were scorched looking and the hard plastic clip part was melted looking)


I have a leak down tester and am going to see where that gets me this week hopefully. Thanks for the advice... Ill post the results.

 

[94K1500KBAR]

Not trying to insult you at all believe me bc I went threw this EXACT problem. Turns out that I forgot to put the vaccum line back on from the back of the TBI to the MAP sensor. I dropped it while putting the TBI riser on and forgot about it by the time I was done. Found it in my driveway a few days later. lol

 

[shibbershabber]

I did double check the line from the MAP sensor... it was there, and it was connected. It did look a little cracked though.

Still thinking I have more of a low voltage issue, even with a new battery and alternator it is still not charging the battery...
we'll see

 

[TylerZ281500]

battery issues could be ground straps, bad ground, batery cable.

 

[VorTecxas]

Check your timing. My friend (the gold truck in my sig, it's a '95) recently had the exact same problem. It ran like crap, no acceleration, trouble keeping highway speed, and horrible gas mileage. Poor guy drove it for a week before I could finally look at his truck. He was running over 25 degrees advanced AT IDLE. Reset the timing and he was golden (no pun intended).

Look under your dash on the passenger side. There is a single brown wire that can be disconnected, disconnect it. If your truck is running at the time, it will run different or die (this wire is your advance). If it dies, restart it. It may run funny.

Set your timing. The tab has a tube on it, which most people incorrectly assume is 0 degrees. You need to rotate your distributor until the TDC line on your balancer is in the first groove before the tube on the tab. This is 0 degrees.

Tighten your distributor and kill the truck. Reconnect the brown wire and restart your truck. The check engine light may stay on for a little bit, but goes away quickly.

Now, if you run Premium, you can actually get away with setting at 2 to 4 degrees initial timing (I set his at 4), since higher octane fuel burns slower. This is why higher performance vehicles and forced induction vehicles require premium, so that they can run a lot of advance without detonation.

 

[shibbershabber]

so when I am looking at it from the front of the engine... I see the tube on the right side of the tab... 0 degrees is in the triangle right next to the tube?

For example...

You must be registered for see images attach

Is the red line or the green line 0 degrees?

my truck is set to the green line.

 

[VorTecxas]

so when I am looking at it from the front of the engine... I see the tube on the right side of the tab... 0 degrees is in the triangle right next to the tube?

For example...

You must be registered for see images attach

Is the red line or the green line 0 degrees?

my truck is set to the green line.

Red line. But like I said before, if you are running premium you could actually set it at 2 (the next high point) or 4 (the next low point) initially. Don't forget to disconnect the brown wire before setting the timing!

If resetting your timing doesn't work, time to break out the fuel pressure tester and voltmeter.

Nothing sounds like it's sucking a little too much air (vac leak) does it?