79 C10 4.8 4L60 Swapped But No Acceleration

[Stepsidejunkie]

New to being a member of the forum, but pulled plenty of great advice from it doing my swap.

My problem is the truck does not accelerate as fast as it should. Feels and sounds like a carb'd engine starting in second gear and bogging down. Can't even do a one-wheel burnout in the grass.

Background: Swapped in a 4.8/4L60 from a 2000 Silverado. The Silverado fuel system was a mess, and I had to clean out the fuel rail several times. I cleaned out the fuel tank, put in a new fuel filter, and currently the engine is running off the Silverado tank, sitting in the bed of the 1979.

One of my many mistakes in the swap was not getting the Silverado running well before I did the swap. It had a lot of non-engine related issues, so once the engine was running fine, I pulled it.

Engine starts right up, sounds great, idles smooth and revs reasonable well, but not as well as my 2002 5.3, in Park. Running the original 3.08 rear on the C10, regular size tires, the specs of which were given to the guy that cut down my harness and programmed the ECM. ECM has not thrown any codes.

Because of the sluggishness, I replaced the shift solenoids in the trans, which helped with the downshift, but not off the line acceleration. The trans does start in first (when placed in Drive), and will shift up to 4th, though I have to be going over 50mph or let off the gas. There is some vibration when going 50mph in 4th, like I am stalling the engine while the torque converter is locked up.

Wondering if the torque converter is too tight and not letting the engine rev up enough to get the truck moving?

Any insights are appreciated.

As an aside, the swap was fairly straight forward. We had to do some cutting and welding of the factory exhaust manifolds, and modify the factory transmission cross-member, but installation was much easier than expected. Of course, I have not hooked up a speedometer and am running Autozone oil pressure and temp gauges wired to the windshield wiper.

Thanks.

 

[bucket]

Verify fuel pressure while driving the truck?

 

[JoeR Jr]

When it isn't accelerating, are the O2s reading rich or lean?
Are you sure you're getting 1st gear on launch?
Joe

 

[Stepsidejunkie]

Thank you for the replies. I will hook up a fuel pressure gauge and report.

O2 sensors were reading right on the money at idle, and when I rev, in Park, they adjust to neutral fairly quickly. I have not checked that for awhile though, so will check again. I'll see if I can get a rider to watch them while I actually accelerate and report that too.

Great leads, thank you.

It is starting in first gear, as I can feel all three changes to 4th.

Thanks for your help.

 

[Stepsidejunkie]

I'll need a passenger to get O2 readings, but the fuel pressure is a steady 50psi measured at the shrader valve on the passenger side fuel rail. It will spike for a second, then go right back to 50psi when I accelerate. At idle it is solid at 50psi.

As an aside, I did put a new fuel pressure regulator on it awhile back. Is 50psi too low? It was supposed to be the correct regulator, but maybe it is not correctly calibrated?

Thanks.

 

[Crdude]

Are you 100% its leaving in first? I have seen people confuse 2-3-4 and TQ lock up for being 1-2-3-4.

how fast does it go if you lay into it before it shifts?

Could be a smoked TQ as well.

 

[Stepsidejunkie]

Thanks for the reply. I'm not 100% sure that I'm not confusing converter lockup with shifting to 4th, so I'll check for rpm change. I seem to remember it was significant, but I cant remember.

On the fuel pressure front, after doing a little more research, I think I may have been sold a fuel pressure regulator for a flex fuel engine, and I need the higher pressure of the non-flex fuel. When I pull the vacuum from the regulator I am getting about 58psi at idle, so I will try driving it around at the higher pressure and see if that helps.

More to follow and thanks again for help.

 

[Bextreme04]

You should have around 50-52 psi at idle and around 56-58 at 0 vacuum. It sounds like your regulator and the rest of the fuel system is working properly. What about ignition? Are you sure it is firing on all cylinders correctly? What did you use to tune the motor/trans?

 

[Stepsidejunkie]

Thank you for the reply. I'll have to ask the guy that cut down the harness and re-chipped the pcm what tune he put on it. I just assumed he left the stock mapping.

However, I swapped out the 50psi flex-fuel regulator for a 58psi unit, and it transformed the engine. Much more responsive, better power, etc. Idles at 58psi and under load/zero vacuum it is about 64psi.

I still think the torque converter is too tight as the trans is tugging on the truck when stopped in Drive. Not sure how to fix that, but probably something for another thread.

So the main lesson for this thread is to make sure you are running the right fuel pressure regulator for your engine. Many of the eBay ads say their regulator will work for flex and non-flex fuel, but that is not the case.

Second lesson I learned was I should have bought a $1000 Suburban that I could have test driven as my donor vehicle vs. the $125 non-running POS I used. Probably only saved a few hundred dollars overall, but had a lot more agrevation.

Thanks to everyone for their help.