Hi all, I have a 99 Tahoe 5.7l with 145,000 miles that I just replaced the spider fuel injection out with the MFI conversion kit. I did this because the fuel pressure was bleeding off making it very hard to start in the mornings. I was just going to replace the fuel regulator but decided to do the conversion while I had it all apart. Now the engine misses slightly at around 2000 rpm’s. I replaced the upper plenum gasket and torqued it to spec. Then trying to solve the problem I replaced the distributor cap and rotor since it looked in rough shape. The Tahoe doesn’t buck quite as bad now but still noticeable. It idles fine (maybe a tad more rough than it use too) and seems to have the power it use to have. I checked the fuel pressure and am getting 50-55psi at idle and jumps up to 60 psi after giving it some gas. The fuel pump was replaced less than a year ago and I just put a new fuel filter on it right before I changed the injectors.

Do you think I could have a weak fuel pump causing this?

Would the timing need to be recalibrated after new injectors?

Does it take some driving of the vehicle for the computer to learn its new injectors/distributor rotor and cap?

Or is it most likely I have a vacuum leak that I cannot find?

Thanks in advance

 

My old '99 5.7 Yukon had an erratic miss when under load. I had to change the cheap plastic body distributor at 95k miles on it after going through wires, caps, rotors, plugs, etc.
I too had to change the spider injection system due to leaky injectors. I drove it to 200k miles and sold it running fine.

 

That could be. I just figured it has to be something to do with me switching out the injectors since it ran fine before. The only problem I was trying to fix with the injectors was the hard starting after it sat over night.

Last night I tried the spraying carb cleaner trick around areas that could have a vacuum leak but couldn’t find any leaks. I’m leaning towards the fuel pump not delivering enough pressure. Everything I’ve read is that it needs to have 60-65 psi to run properly. Mine won’t get over 60psi. Idles at about 53-54. Could a faulty relay cause it not to have enough pressure at highway speeds? Runs great till about 2000 rpm’s just cruising at 65mph.