What might be causing sluggish power?

[BrianBrianBrian]

This is going to be a long one so bare with me....


1998 2dr 4x4 LS Sport
168,300 miles

All items below are new.

• GM Goodwrench 1996-2000 Truck 350ci/255HP 5.7L Engine
• BWD Fuel Injector - MFI
• Spectre Performance HPR8038 Air Filter
• Dorman 626-105 Heater Hose Assembly
• Stant 45119 SuperStat Thermostat - 195 Degrees Fahrenheit
• ACDelco 19244500 GM Original Equipment Engine Oil Pressure Sensor
• OEM 8824 Neutral Safety & Reverse Light Switch
• Dayco Belt Tensioner
• Duralast/Crankshaft Position Sensor
• Duralast Gold/Starter
• ACDelco 335-1068 Professional Alternator
• Bosch 09768 Premium Spark Plug Wire Set
• Automatic Transmission Flywheel Flex-Plate
• Torque Converter, 700/4L60/65E, 298MM
• 4L60E Rebuild kit, M. W/S, 97-03 FIBE
• Filter, 700-R4 82-93
• Band, 4L60E 2-4 HI ENERGY
• Plate VB Seperator 4L60E
• Ignition Distributor for GMC Cadillac Chevy Pickup Truck SUV Van V8 5.0L 5.7L
• ACDelco 214-1080 GM Original Equipment EGR Valve
• ACDelco 41-993 Professional Iridium Spark Plug (Pack of 1)
• Dorman 800-401 Heater Hose Quick Connect
• Delphi AS10015 Ignition Knock Sensor

I've been driving it around for a year now with with no problems other than a P1870 code which is next on my list of things to fix (TCC regulator valve - Fitsall). While it drives ok, however, it really feels sluggish and a need to press the pedal down just to climb a short hill from a stop. While in this process the exhaust sounds much different almost louder than what I remember from before all these new parts. Now that I think about it, it almost feels like 1st and second gear is absent, but there's no way??

When the engine was installed,
A mechanic friend of mine set the timing with the old finger test... starts just fine. My scan tool says timing advance at idle is 21.5. Not sure if this is good or bad? or can it be improved?

He also installed the new spider Injector. Could this have been installed incorrectly? If so would it still be driveable as I've been driving it around for a year now?

I've seen where some folks have pointed to a fuel filter as a possible cause?

Does anyone think it could be related to me fixing the P1870 TCC regulator valve. I don't see how that would have any effect on the power?



Is there a way to use my OBDII scan tool to diagnose the problem? I've tried searching the entire internet for the correct computer readings on a 98 tahoe should be at Idle and compare them, but to no avail. Oh, and for the record, I just passed emissions!

In any case I'm at at a loss as to where to begin. I would be so grateful to anyone that could brainstorm this with me! I've attached screenshot of the codes that my scanner puts out if that helps.


Thanks Brian

 

[Cameron]

Timing needs to be set at almost 0 degrees I believe and has to be set with a scan tool.

 

[BrianBrianBrian]

Timing needs to be set at almost 0 degrees I believe and has to be set with a scan tool.

Thank you for the reply Cameron.

Does timing have a direct correlation to horsepower and torque? If timing is off by just a couple of points (advance/retard) will this cause the engine to underperform, feel sluggish when pushing the pedal down?.

I guess when you think about it logically, if the piston is getting sparked at its lowest stroke then the compression will be greater, thus more power. As opposed to the spark occurring while the piston not fully closed. Much the same as trying to jump high in the air using only your ankles as opposed to using your knees, ankles and back.

While this makes sense, I wouldn't think the engine would even start if the timing is off, or at least hesitate? My truck starts right up on the first stroke. Anyone have a recommendation as to where/who might be able to perform a timing test and/or adjustment that won't cost a fortune?

 

[Cameron]

An obd2 scanner that can show live data of the sensors can show you your timing advance. And you said the exhaust seems louder do you have catalytic converters on your truck that would cause a change of tone when they start clogging I noticed you said a possible fuel filter you can get a fuel pressure tester and check that to rule it out

 

[Cameron]

Then again your engine could be fine and your p1870 is causing tc failure

 

[BrianBrianBrian]

I'm just trying to guess what all could be the cause of this issue. Fuel Filter? Timing? Fuel Pressure? or other? While I can go through each little scenario and test or replace, I thought it'd be easier to play "process of elimination" before getting dirty.

A little background: The old engine spun a bearing so rather then rebuild I just bought a brand new GM crate motor. And seeing how I was already greasy and had the engine out, I also had the tranny rebuilt and replaced a lot parts. When putting everything back together, if it wasn't new, I cleaned it up and made it look new.


That said, I'm able to eliminate a lot of probability as to what might be causing this sluggish power, or at least add to the end of list of things to try. New Engine, New Injectors, Spark Plugs, Wires, Distributor...list goes on. Fuel filter and Fuel pump are original, we did check the pressure when the engine was installed and everything was within range.

*****

I just did some research while writing this and I'm thinking that I should dive into checking the MAP sensor. From what i gather, the Map sensor measure the volume and density of the air entering the engine so the computer can calculate how much fuel is needed to maintain the correct fuel mixture.
"A dirty wire (which may be the result of a defective self-cleaning circuit or external contamination of the wire) can make the sensor slow to respond to changes in airflow."

I do recall cleaning this thing with water, maybe I somehow screwed it up. Anywho, I'll start here and check back. I'm still open to suggestions?

 

[#1taho]

It all maybe brand new but if it's not set up right you will be sluggish. (Timing and such). How is the fuel pressure ? Was the proper injectors put back in ? What can came with the crate motor ? All great things you have done. Hope we can help you find it as I am sure you have a ton of cash in it by now.

 

[BrianBrianBrian]

It all maybe brand new but if it's not set up right you will be sluggish. (Timing and such). How is the fuel pressure ? Was the proper injectors put back in ? What can came with the crate motor ? All great things you have done. Hope we can help you find it as I am sure you have a ton of cash in it by now.

There's certainly no argument there! To the best of my knowledge everything was put back in correctly, the only thing that I had someone do for me was connect the new spider injector in the manifold and then seal it. I probably could have done it but he's mechanic, so.

How is the fuel pressure ?
Can't recall the numbers other than it was checked when trying to crank it for the first time.

Was the proper injectors put back in ?
I'm pretty sure I bought the correct/ proper injectors. https://www.amazon.com/ACDelco-217-3029-Original-Equipment-Injector/dp/B000NW8EU8

What can came with the crate motor ?
Bought it from Jeggs, short block, never cracked the shell open to look.

 

[#1taho]

There's certainly no argument there! To the best of my knowledge everything was put back in correctly, the only thing that I had someone do for me was connect the new spider injector in the manifold and then seal it. I probably could have done it but he's mechanic, so.

How is the fuel pressure ?
Can't recall the numbers other than it was checked when trying to crank it for the first time.

Was the proper injectors put back in ?
I'm pretty sure I bought the correct/ proper injectors. https://www.amazon.com/ACDelco-217-3029-Original-Equipment-Injector/dp/B000NW8EU8

What can came with the crate motor ?
Bought it from Jeggs, short block, never cracked the shell open to look.

Check the paper work that came with the motor. The may be an up grade or something else. I am sure the injector will be correct. I would check fuel pressure and when was the last time you changed your fuel filter ? Last make sure the distributor is in correctly and timed correctly. Is the any check engine light on ? If so correct the codes and retry. I would bet mostly timing. My brother had a 98 z71 5.7 L I did the intake and didn't get the timing back 100% and it was a dog. Had it done with a scanner and back to good as new. Hope at least so of this helps.

 

[BrianBrianBrian]

Well after about a 1/2 gallon of Fast Orange hand cleaner, I've diagnosed the problem, fixed it, and now the world can get back to spinning.

CHECK LIST
Pass! - Fuel Pressure tested 61.
Pass! - No leak in the pressure after turning the key off
Pass! - MAP sensor reading was accurate
Pass! - Timing was a little advance (3) not bad. Set to 0

FAIL! - Exhaust leak where the exhaust manifold connects to the pipe. Donut gasket.

So, I guess this is where it pays to be a Mechanic. Had someone say they were hearing an exhaust leak.

Since the headers, exhaust manifold, and gaskets were all new and tightened to spec my next thought was maybe the donut gasket? Autozone $6 each. + some bolt buster.

PROBLEM SOLVED! I never knew that just by having a leaky exhaust would dampen the performance of the engine that much. Once I installed the new donuts, the muffled sound disappeared under heavy load and the throttle response on take off was back to perfect.

Thank you to everyone that offered their 2 cents, while it wasn't any of those issues it at least got me started in crossing things out!