So I have an Issue with my newly acquired 1999 Suburban with the 5.7 and 4L60 in it and 350,000 miles on it…

When I pull out from a stop and I mat it to the floor and try to accelerate the engine only revs to 2000RPM and accelerates slowly almost like it’s in some sort of limp mode.

Tried cleaning MAF and throttle body, also checked trans Fluid and engine oil. Tried unhooking battery to reset electronics.

has anyone else have this issue? It’s only worked correctly once but then on same drive went back to not revving… if I put shifter in 1st and accelerate it will eventually go past 2000rpm but it takes a while.

What else could I try to fix the issue?

 

My take is fuel pump. You need to check the fuel pressure, could be just a regulator issue, but IMO lack of fuel.

 

gotcha, I will check the pressure tomorrow, it also run and revs fine at idle and will continue to rev when you hold the peddle down it just feels super sluggish. Hopefully it’s the regulator or a clogged filter so I don’t have to drop the tank!

 

Have you put a scanner on it to see if any codes come up? Is the transmission slipping maybe, i know it usually will rev up and not take off like it should. The 2000rpms is what's kind of puzzling me, maybe the cats could be clogged and that's why it's not revving very high or going anywhere. That's about the only thing I can think of off the top of my head. Good luck and let us know how you are making out

 

2 great suggestions already posted.

if fuel pressure is ruled out. rule out the cats by bypassing them. take the pre cat 02 sensors out of the exhaust and test drive...if it revs up...the cats are clogged.

 

Alright, since I got the suburban with an unknown service history and parts being cheap and fast to get ahold of I starting throwing parts at it knowing I’ll be keeping it for a while.

it was not the fuel pump. Replace whole sending unit as it did have 350,000 miles on it. I replaced the fuel filter. Removed line at intake and blew out line to make sure they weren’t clogged. I haven’t pulled the intake to check injectors or the pressure regulator…

when I first checked the codes on it there was nothing then a day later a O2 sensor code came up… thinking it was the Cats I ran some of the SeaFoam you run from the throttle body through it and allowed it to hot soak. Then ran it for 100 miles code didn’t come back but still won’t accelerate.

now to yesterday…

I was driving and still not acting right and filled up with fuel and went to put in the info on my ScanGuage2 and thought it check the codes that’s when I found a pending code of P0785 and that’s when it all made sense… a shift solenoid malfunction code.

so next up I’m gonna crack the transmission open and see if that’ll fix it. I’ll have another update once I get it done.

thanks for everyone’s input and help.

P.S. The ScanGuage2 is amazing to have dash mounted in anything with an OBD2 port (this is NOT a paid ad)

 

does it rev past 2000rpm in neutral...if not, its more than a shift solenoid.

 

yes it revs fine in neutral and even acts fine in drive sometimes for a few accelerations then starts to act up.

 

350k miles that trans is ready for a rebuild. Especially when it was bought used with high miles. I would not even screw around with a solenoid.