Hey all, i know on paper the 5.8 is supposed to be pumping out about 200hp. I was wondering what the typical performance of the 5.8l full size truck should be. I noticed yesterday that the truck tends to struggle to get to (and maintain) 65 mph. I hadnt really noticed it until i was driving home last night on the highway and was driving into a 18 mph headwind. The pedal wasnt floored but was pretty close to it. Is this normal since the truck itself was geared for 55 mph speeds, or do i need to diagnose a power loss problem? BTW, only performance upgrade is a k&n intake, engine is 5.8l jasper with only 650 miles on it. Thanks!

 

How much power that makes it to the wheels depends on several factors:

1. Auto or Manual transmission?
2. Axle gearing currently in the truck?
3. Tire size?
4. 2wd or 4wd?
5. Any modifications?
6. Last tune-up with plugs, wires, cap & rotor?
7. Check Engine Light (CEL) on?
8. Have you run the Key On Engine Off (KOEO) tests and stored (Continuous Memory) display?

 

1.Auto
2. Stock
3. 31x10.5
4. 2wd
5. K&N intake
6. With new engine...650 miles ago
7. CEL has never come on so
8.have not run any tests

 

Re: Question 2......these trucks come with a variety of gearing options from the factory. Check the door jamb sticker for the axle code. Post it here.

Re: Question 7/8......You can have an issue that would cause an error code on the KOEO tests without triggering a Check Engine Light. Highly suggest you run them.

Since this is a new engine did you set the base timing to ~10 BTDC with the SPOUT out?

 

Axle code is 19

Ok, ill have to run the tests

And the engine was put in by a mechanics shop so im not sure. Ill have to check that as well

 

Just for reference my '88 5.0/5 speed wheezes on the interstate as well. It'll do 70 on level ground but the slightest grade and its huffing.

I'm looking at repowering mine for the same reasons.

 

Axle Code 19 is an open 3.55 ratio rear axle.


3.55 is a good al around ratio it is starting to be negated with those 31" tires. Any specifications on the engine you had installed?

Any other aftermarket add-ons like off road light bar, big mirrors, etc.? Items like that create a lot of extra aerodynamic drag.

What kind of MPGs are you getting? I assume the PSOM was recalibrated for the taller tires?

 

I think you've got power loss somewhere. I have 3.08 gears and 235x75x15 (basically 29" tires). I can run at 85mph all day long with power to spare. Consistent 13.7mpg mixed driving.

I'd take it back to the mechanic that did the work. Did the Jasper come with new injectors and compatible ecu? Or is it set up to run on the ecu that came with the truck?

 

Ok, just rsn the eec-IV koeo test, only code was 33/egr valve not opening. Took it off and sure enough, it was stuck. Cleaned it up and now its moving freely. Would the egr stuck closed do that??
I have a headache rack on the truck. That's the only exterior add on.
BTW. Its a standard rebuilt 5.8, VIN was referenced for compatability

 

Yea something isn't right. I have the same setup, but on 33" tires, live at 7200', and can bury the speedometer if desired. 5% grade at 70mph for miles isn't a problem either.

How's the vacuum system? My EEC-V told me I had insufficient EGR flow, when in fact it was pulling too much EGR. The computer basically just pointed me to the correct system, but was wrong about the actual problem.

 

Check your ignition timing, factory spec is 10deg before TDC with the spout jumper plug pulled to disable computer advance, you want to verify the base setting but also that it advances some when the spout is plugged back in. It's also a common tweak to throw 2-4 degrees more advance in but be aware this puts the motor closer to detonation so you have to experiment a little to find a good setting, the way the truck is used and the engines condition all affect how much advance it will tolerate before detonation(pinging) because audible. More ignition advance produces more torque and horsepower, the difference in engine performance between 0 advance and 10-12deg is anemic to pretty peppy.

 

I haven't done my 5.8 swap yet, and I have a 5.0 with 3.55 gears and 31 inch tires and as worn out as the engine is I have no problems running 70-75 even on a medium hill. So like everyone else is saying. I'd check timing.

 

Ok, so i checked the timing, and it turns out whoever set the timing, set it with the spout still in....So i took it out, turned all accessories off, placed the truck in neutral and it showed to be below 0...
I adjusted it and it seems to have a whole lotta pep now. I test drove it only for about 8 miles but it consisted of 60-70 mph zones and it seems fine now. Definitely easier to get up to and stay up to speed.

 

Awesome. Glad you got it figured out.

 

X2....It had to be something simple. Thanks for the reply back.