TBI_GUY

SORRY FOR THE LONG POST GUYS, I'VE BEEN FIGHTING THIS ONE FOR A WHILE.
Needless to to say I'm a TBI guy and this vortec crap is ticking me off.
This was my Father's Tahoe from brand new and I just bought it from him last year and ever since, it's been getting bad mpg.
5.7 Vortec / 4l60e / 2wd / 4dr
He replaced the engine with a brand new GM longblock in 2012 at 209k
Then he had the transmission rebuilt at Ed's transmission in 2013 at 219k
I noticed immediately after the new engine, this thing did not have near as much power as before (the old one had a dead cylinder)
And then after the tranny rebuild the power decreased again (strange I know)

At first I was getting 12 mpg no matter what I did, how I drove, city or hwy whatever.
Then it started running poorly and cutting out then eventually not starting at all. I installed new spider injectors with the BWD MFI unit from O'Reilly, cap rotor and spark plugs (wires looked good).
Back to running smoothly.
Only problem is the mpg went down to 8mpg, still runs good with an ever so slight bump in the idle.

The truck has new front O2's and a new bank 2 cat due to the p0141 code (All this was before the injectors and stuff)

The truck also does this weird bucking like behavior after I've been driving it all day long. Right when OD hits at 45mph, the rpm gauge kind of bounces up and down a little maybe 300 rpms or so and the truck kind of bucks but its not cutting out.
Again this only happens when I've been driving it for more than 2 hrs from place to place.
Some other thing to be noted are:
First thing In the morning when I put it in reverse, not only does it slam into gear like it always does, it's been making a popping or clunking noise, and it won't move until I step on the gas a little then another louder pop then it'll go.
As I said it slams very hard into reverse when cold and harder than normal into drive.
When it's all warmed up it gets a little softer but reverse still slams a little.
The 1-2 shift is a little hard and sometimes inconsistent as well as the 2-3 shift
It needs front end work, all the ball joints need replacing as well as the Idler and Pitman and a frame bushings.
Rear leafs are COMPLETELY shot
Rear end is original
Odometer reads 257k miles
As I said before the engine seems to run good, doesn't blow smoke, no gas smell even, no Engine light or anything
But the truck does seem slow, I'd kicks out of OD on the hwy with the cruise on going up even small hills, and it can barely pull a medium size trailer unloaded. Seems to take forever to get up to 70 even with my foot in it. It was NOT Like this before all the work

5.7 Vortec 8mpg and slow

What do you guys think?

Scotiapilot

I would check exhaust back pressure. Timing too!


if I am not mistaken there were two options for 5.7 tbi engines. One was graded for 3/4 tons and had a dif cam profile for low end TQ but had horrid HP and crappy gas mileage for nothing. So there is another issue for ya. LOL

justimagination

[QUOTE=Scotiapilot;321562]I would check exhaust back pressure. Timing too!


if I am not mistaken there were two options for 5.7 tbi engines. One was graded for 3/4 tons and had a dif cam profile for low end TQ but had horrid HP and crappy gas mileage for nothing. So there is another issue
************************************************** ************************************************** ************************************************** *********************************
Times two on the exhaust, either catalytic converter or muffler, of course it's not possible to check fuel mileage with either disconnected or you will go to jail. I'd put my money on it. If my Tahoe had that much wrong, then bye bye. JMHO, AND GOOD LUCK

TBI_GUY

Yes I'm aware of all that but this truck has the VORTEC 5.7 not the TBI 5.7 and from what I read they are all the same

TBI_GUY

[QUOTE=justimagination;321566]Yea she's got alot wrong but I can't give up on her I used to ride around in this thing as a kid, as I said it was my Father's since new and she's still very clean inside and out.

I'm willing to put in the wrench time I just am at my wits end with this issue. Someone told me a while ago to check Exhaust back pressure so being the second time I've heard this, what would be the best way to do so?

Thanks for yall's help guys I really appreciate it

cleveland63b

get a gauge and install it where the 02 sensors go, anything above .5psi is bad. Or you could removed the front 02s and drive it, see if theres a noticeable power difference.


Have you checked fuel pressure and volume?

TBI_GUY

I checked the fuel pressure before I did the injectors and it was fine but I'll check it again. I'll also do the test with a gauge in the 02 sensor holes.

I'll get back with results
Thanks again

Scotiapilot

Bingo, I forgot. Love the vortec.

TBI_GUY

Ok guys my fuel pressure is 50 psi with the key on engine off
56psi at idle and it will jump up to 60 if I rev it hard

I haven't gotten to unscrew the O2's yet I'll get to it tonight and keep updated

TBI_GUY

Ok guys I yanked out the front 02's and no change.

I've been thinking maybe it's the transmission.
Here's the story: My father still owned the Tahoe when the transmission was rebuilt at ED'S Transmission. I advised against it at the time because I have always liked Eagle Transmission and had heard a few horror stories about Ed's. Well needless to say he went ahead and took it to Ed's. But unfortunately my Father was only available to take it in during the night hours due to his work schedule, so the Ed's manager told him he could drop it off at any time just leave the keys in the night drop. So he dropped it off about 1 am.
A few days later he gets a call that they are finished with it, and it has a supposedly "complete rebuild" that was $1800 and change after everything. Again due to his work schedule he was only available at night. So he picks it up at about the same time 1am or so.
I found it strange him not even meeting the people that rebuilt it.
I then started thinking maybe they thought because he was naive enough to leave his truck in a dark parking lot in a well known "not so great" part of town and then seems to not even care to meet the people whom he will be paying $1800 to, that they could skimp on a few parts or maybe even throw in a used unit and he would not notice or care or both.
I don't know what the policy at Ed's is but I do know there are alot of shops especially around here that will do shady things and as they say "screw you over".
I don't mean to offend anybody in any way and I sincerely do apologize if I offend you if you are a mechanic or you work at Ed's transmission, but here's why I think something just isn't right.

The day he got it back he calls me up and asks me to test drive the truck because he says he thinks somethings wrong.
So I take off and from 1st to second gear BAM! second to third the same but not as hard.
I tell him that I think they didn't rebuild it right because that was way harder of a shift than any shift kit I've ever had. I'm talking drink spilling jerk seriously.
So he talks to the Ed's manage over the phone and he says its normal because they put shift kits in all their rebuilds and if he (my Father) would like he can install a softer servo spring, my father agrees.
So once again he drops it off at 1am having no face to face contact with anyone and gets it back a few days later and it shifts a little softer but still hard.
My father says screw it and settles for it.
Well a few weeks later I drove his truck to test the transmission again because he says it drops into gear hard now.
So I shift it from park to reverse and BAM! ( I thought It snapped the drive shaft at first) from reverse to drive bam again. So then I drive down the street in it and I hear this whining that only happens on acceleration, goes away instantly as soon as you let off the gas. It's pretty loud.
I know it not the rear end because it changes tone everytime it shifts to a different gear. Like it will start like a low whine then as you accelerate it will get higher and higher pitched then when the transmission shifts it will go back to low whining and so on.
So now it's:
Shifting hard
Slamming into every gear from park
Whining

Also my Father said ever since the rebuild he hasn't been able to get over 14 mpg, before it was above 16.

So I purchased the truck from him for $1500 about a year ago now and a few weeks after i bought it, it started bucking right around 40mph right when it shifts into OD. It will shift into OD then the truck just bucks a little as if the TC isn't staying locked or something (it's not TC shudder, I've had that before) also the rpm gauge will Bounce up and down about 300 rpms or so. I have good fuel pressure and every fuel related component besides the fuel pump has been replaced recently and even that was done about 2 yrs ago (and if it was the pump I'm sure it'd long be dead by now)
And just recently it started doing this thing in the mornings where it slams into gear (reverse in this scenario) then when I let my foot off the brake to back out of the garage (no gas) it won't go.
Then if I press on the gas for it to go I hear a loud metal click, or snap then it moves fine.

Also the truck seems excessively slow as if Im constantly pulling a heavy trailer or I'm driving a 1 ton truck with the same engine, (it just seems sluggish performance wise), also very bad gas mileage.

So my questions to you guys are:
Does "the bucking" sound like the TC not staying locked?
Could the click or snap I'm hearing be from the transmission? I park on level ground and use the parking brake so the weight of the vehicle is completely off of the transmission.
Why is it slamming into gear and shifting hard?

All arrows are pointing to this tranny so with that being said could theoretically something inside the tranny be maybe dragging or too tight or mis-adjusted causing the sluggish performance whining and or bad gas mileage?

Do you guys thing my Father (now me) got screwed by Ed's transmission?

Again sorry for such a long post thanks for any and all replies.