Carbureted LSX forum - Carb'd 5.3 with issues...

So...I have a 5.3 out of an '02 tahoe or suburban that we've installed an edelbrock 7118 kit on with the intake and timing module into a 71 Chevelle. Has a new holley 600 on it (new not re-man). Thing will start up and idle great but has zero, and I mean ZERO power. It's like it does not have enough timing. I have tried all 6 timing curve pills provided with the kit, but the car is just a dog. We've tried a couple carbs on it (this new holley is the latest and we're sticking with it). It doesn't pop or miss really, other than an occasional hesitation when it's cold. Has anyone else seen this kind of problem when carbureting one of these motors?

my guess is a box issue.

The MSD ones are programable the edelbrock ones are not.

Tim

Is it an Edelbrock , or an MSD ?? I didn't think Edelbrock had pills for thier box ?

I googled the kit number and it shows the kit that comes with the edelbrock . I have seen a few people running the Edelbrock box in a mainly stock setup with decent results though .

What pill are you using and what are the timing specs on it???

what do you mean zero power? will it rev up in neutral?

I ran the edelbrock on my car for a year and had no problems.I used tha#6 chip it is 35 deg.of timing and went 11.13 at 122 so unless the box is just messed up it should work for you.

The car will rev fine in neutral...supposedly it's an edelbrock box made by MSD. I talked to Edelbrock yesterday and they were about as helpful as a burnt out light bulb. I've tried the #3 pill and the #2, it has the #2 in it now. It's crazy, the car will start, idle and free-rev fine, put it in gear and back it out of the shop and you have to go to the floor with it to get it to pull off or rev under load. I am going to swap the plugs in it for another fresh set and see if that helps at all. Any ideas on what a correct gap would be for these motors carb'd? I really appreciate everyone's help!!!

Mine are gapped at 35. What kind of fuel pressure do you have.and also if you have a stock cam in there it is probably on a 117lsa or something like that for the fuel injection and it is going to be gutless with a Carb.

I ran the edelbrock on my car for a year and had no problems.I used tha#6 chip it is 35 deg.of timing and went 11.13 at 122 so unless the box is just messed up it should work for you.

That's what I was thinking , I know of a few people who are running a Edelbrock box with pretty good results . I know the MSD is supposed to be better because it can be tuned, but I have heard some pretty impressive info on the Edelbrock as well .

What do plugs look like? Have you played with jetting? Could there be a trans issue, shifter not adjusted properly, etc?

Sounds like it is taking off in 2nd or 3rd gear? My stock cammed 4.8 runs harder than 5.3 and 6.0 trucks I have run across, so the cam should not be a issue. But with 1st gear out, it is a slow Performer off the line till it gets into rpm.

make sure you have fuel pressure and no vacuum leaks

Is it possible this could be an intake gasket not sealed correctly causing major vaccumm leak. And I have had msd stuff come out the box not working correctly...So it can happen.

Yeah...I looked at the transmission linkage, shifter adjustment, etc, but it's the same in reverse as drive. The engine struggles to rev under load, even as little load as backing out of the garage. I am going to pull the plugs tomorrow and take a look at them, I really appreciate everyone's feedback!!!

sounds like fuel starvation to me, what are you using for a fuel pump and regulator? have you verified the regulator is properly adjusted? - there is a right and wrong way to set the regulator

I'm with 3 pedals on this. I wonder if maybe the floats aren't properly adjusted. If nothing else if you could swap the "NEW" carb out with a friend or a known good carb you could eliminate one possibilty.

The fuel pump is a holley blue pump, set at 7-8 psi. Both carbs I have tried have exhibited the same issue. I'm not 100% sure on what the issue is, but I am going to check the plugs and the fuel pressure tomorrow. Thanks again, keep the ideas coming!

Sounds like a fuel issue to me, or the trans, rear diff is somehow binding.

I wonder if the box/pill is not advancing the timing?? Does everything have a good ground??

Mixing up the firing order will make a car run like that.

Take a non-contact thermometer and check the temp of each exhaust port when the car is running. See if any of the cylinders are not firing.

make sure your power wire goes directly to battery get a good ground on the frame check for vaccum leaks and make sure you have good fuel pressure.

ok...so we pulled the plugs and it gets even more odd. One side of the motor, the plugs look like they are all firing perfect, good color and do not look fouled. The other side of the motor looks like they have not been firing at all. Would it be possible that all 4 coil packs are bad? I'm thinking no, but is there some other explanation such as a ground wire for that bank that is somehow missing? We had the coilpacks off when we installed the intake, but everything is plugged in and there does not appear to be any wires missing or pins in the connectors that are bent. Anyone seen anything like this before?

Sounds like you may have a bad box. Maybe MSD will let you swap it for a 6010?? That way you can use pills or program it. You could swap wires or coils and see if the problem follows but I doubt you have 4 bad packs. There is a common fault between the 4 of them, most likely.

you can't tell by the sound of the motor that it's missing 4 cylinders? really ....?


yes the coil connector for some reason at the white connector could not be firing the entire side, perhaps a break in the wiring or missing/bad ground on that side.

Mixing up the firing order will make a car run like that.

Take a non-contact thermometer and check the temp of each exhaust port when the car is running. See if any of the cylinders are not firing.


Swap coils around and do like he said if you don't have a thermometer use a spray bottle and some water to see which ones sizzle the water off the quickest. If the water doesn't sizzle off the cylinders not hitting.

unplug the main harness connector and make sure all the pins are fully inserted into the connector body. you can see if some are lower than others, and they may not be making contact.

Is the motor reving under load, but car barely moving or is it struggling to rev under a load?

Did you change the cam or timing chain?

So, sorry for taking so long to get the resolution up on this one but we were facing a couple of issues. First, the MSD box wiring harness had two pins reversed on the passenger side coil pack connector (the power and ground for all 4 coil packs). Once we resolved that (and yes the car would crank and idle on 4 cylinders) it turned out that the power going to the box was not sufficient to run it. Once we resolved the power issue, we verified the fuel pressure and all was good. The car now runs really well and seems to have plenty of power, even on the stock timing curve. I appreciate all of the ideas and help, this one was a pain but turned out really nice.

Good news