Hot Rod Forum banner

1 - 20 of 57 Posts

·
Registered
Joined
·
37 Posts
Discussion Starter #1
I just finished rebuilding the 454 on my 1995 Suburban. I broke it in and then felt comfortable enough to take the 5k lb boat to the lake. There are some decent hills along the way and each hill felt like I was dragging an anchor behind me. The speed would slowly start to decrease from about 70 mph to the 50s. I have never felt so defeated in my life after spending the time and money that I have in this rebuild (not to mention all the other items I have upgraded on the drivetrain). But, here is the thing, the engine is acting exactly like the last one I replaced. The prior engine did the same thing when I hit any sort of incline. This new engine is fresh and has some additional horsepower from the new cam, domed pistons, etc. So, my question is whether or not it is the engine after all? Is it possible that the TBI, the computer, the cat, or something else is causing the problem? On the old engine before I rebuilt the current one and replaced it, I did try removing the cat and going up some hills to see if that changed anything and other than the noise, it didnt seem any different. I have also taken the throttle body apart, cleaned it, and put in new injectors. Lastly, I replaced the computer with a different one to see if that made any difference. None of those things changed the power issue. Nothing makes any sense. The engine runs great and sounds perfect. The only issue I am having is with the lack of power when pulling. It has a new tranny which I know isnt the issue because it had the same lack of power with the old tranny before it gave up. I have changed the gears in the axles from 3.73 to 4.56. So, it should have tons of power from the new engine. The tranny is solid. And the gear ratio should help it pull just about anything. But, when it comes time to pull, it falls flat on its face. Any help would be greatly appreciated. I am at my wits end with this thing.

1995 K2500 Suburban
Gen V 454 (TBI)
4.56 Gears
35" Tires
4l80E Trans
 

·
Registered
Joined
·
307 Posts
What was the original engine compression compared to what you built? What cam did you install? If you significantly upgraded the power potential of the engine, have you had it tuned to better take advantage of the upgraded power available? Is the base timing set correctly? I believe to set the base timing you must disconnect a wire behind the glove box. There are many things that can be holding the engine back.

Keith
 

·
Registered
Joined
·
37 Posts
Discussion Starter #4
blwn31 I wouldnt say that I significantly upgraded the power potential on this engine. I actually tried to keep it relatively stock and just give it a little advantage. Below is what I have done to the engine, but the thing is, it is running just like the old engine that I replaced because I thought that engine was old and tired.
I have adjusted the timing on both the old engine and the new and it didnt make much of a difference. The new engine is still in need of a computer chip to fix the timing because it is so far advanced. When I unplug the tan wire with the black stripe under the glove box, I can adjust the timing to the point where it runs nice and crisp. Thats around 12 BTDC. Stock calls for 4 BTDC, but the new cam doesnt like that much. The reason I am in need of a new programmed chip is because when I plug the wire back in and start the truck again, the computer has moved the timing all the way to around 25-30 BTDC. That is just a guess because the timing mark is well off the timing plate to be able to even read the timing anymore. Anyway, I am looking at getting a chip from TBICHIPS.com to get the computer to play nice with the cam. But again, even with the old stock engine timing being right around where it called for, it ran the exact same way on hills which makes me think that it isnt the timing (even though I know the timing does need to be adjusted for better performance/ fuel economy).
I am starting to lean towards the fuel system. That is the only thing that really makes much sense considering that both engines are doing the exact same thing. Again,both engines sound and run perfect until I hit an incline which is where I am starting to think that maybe the engine isnt getting enough fuel. I really cant think of anything else.

Here is what I have done to the engine:
New bearings all around
New Lunati Cam & Lifters 60200LK 207 213 .495 .515 112-LSA
New double roller chain
New Speed Pro 10cc dome pistons
New piston rings that I filed to fit. All bores were in really great shape. I just honed them all and tightened up the ring gap a little.
I did clean up all the ports and did some bowl blending to get as much as I can out of the peanut heads.
I put an adjustable fuel regulator on the TBI to adjust the fuel pressure.
Everything else is pretty much stock.
 

·
More for Less Racer
Joined
·
19,370 Posts
What is the fuel pressure doing when the engine loses power??

Sounds a lot like a pump that can't keep up, or a partially plugged fuel filter or strainer "sock" in the tank on the pick-up tube.

In tank pumps do wear out with age.

What you are seeing with the timing when you plug the computer control back in after doing the intitail setting with a light, that is normal....the computer advances the timing for best idle and emissions according to inputs from throttle position, MAP, engine rpm, coolant temp, O2 sensors to maintain the highest efficiency it can. As soon as you drop it in gear the computer will adjust timing on the fly as any input signals change....throttle position, engine vacuum(MAP sensor), rpm, etc to constantly try to be as efficient as possible in concert with the preprogrammed fuel and timing tables in the chip.. The knock sensor is used to keep things from getting out of control with tining when under a load.
 

·
Registered
Joined
·
307 Posts
While I'm not that familial with TBI engines/tuning, a '95 Burb only had 230HP with 325lbft of torque in stock form. You are pushing around a 5.5K lb vehicle then hooking up another 5K lb boat, which puts you over GVW, it's gonna struggle towing uphill. I'm guessing your turning about 2500 in OD at 65 and about 2900 in 4th with O.D. off. With the new cam and pistons and possibly an additional 75-100HP you are only talking a little over 300 HP. I would talk with some tuners and find out what chip to get with your mods.
I gave up on gas for towing several years ago, but that's another discussion altogether.

Keith
 

·
Registered
Joined
·
37 Posts
Discussion Starter #7
I agree with the 454 not being the best option for towing out there. I really miss my Cummins. But, I bought this Suburban brand New back in 1995. I know this thing has a lot more to give. Back in 1996, I was pulling a 28' cabin cruiser that weighed over 10k on the same roads I took this smaller boat last week. There is definitely something going on. I just wish I could figure it out.
 

·
Registered
Joined
·
245 Posts
I you can get live data from 02 sensors underl load, see if they are still switching, or locked to lean. If that is the case and injector pulse width has gone max on. That would indicate a fuel supply issue. Either low fuel pressure, flow, or plugged injectors.
 

·
Registered
Joined
·
37 Posts
Discussion Starter #9
I do have a scanner that reads live data. I will try that. How do I know what data is good, bad, or normal?
 

·
Hates: Liver. Loves: Diesel
Joined
·
5,654 Posts
Came here to say what blwn31 said. That engine was a bit of a slug to start with, but it should be doing a little better than what you're experiencing.

Is it a late 95 with OBD2? If so, it should be able to learn a new curve with all of the stuff you did since it isn't a huge departure from stock. I agree that you should get it on a scanner, but if it's OBD2 and the O2s are full lean, you'd get a CEL on the first hill.

If it's OBD1, you have a PROM chip. The ECM can only stray a little from factory. If it's OBD1, I suggest having someone burn you a new chip to match the new components.
 

·
Registered
Joined
·
37 Posts
Discussion Starter #11
I am trying to understand the live data I am reading from this obd1 scanner tool. What does any of this mean? What is good and what is bad?
 

·
Registered
Joined
·
245 Posts
When the ecm is controlling fuel, the 02 voltage will continuously change from high to low. One being rich the other lean. Injector pulse width will also somewhat mirror this. If you create a vacuum leak, the 02 will stay toward the lean side. If you snap open the throttle you should see a momentary lean on the 02 and a lengthening of the pulse width. As you let the throttle snap shut, the 02 will show rich , and pulse width will narrow. That is what normal should look like at idle. Have someone drive it while looking at data. If you see 02 showing lean and pulse width locked wide under pulling condition, you are starving for fuel. Either low fuel pressure or clogged injector nozzles. At our dealership we had an injector flusher that you put in a1/2 gallon of fuel with a pint of injector cleaner. It had it's own fuel pump, hooked up to the fuel rail, and you plugged and disabled the in tank pump. Then started the vehicle and let it run at 1500 rpm till the fuel was gone. They quit using it when everything went to port injection, claiming that injector techology had improved and didn't plug any more.
 

·
Registered
Joined
·
37 Posts
Discussion Starter #14
While I'm not that familial with TBI engines/tuning, a '95 Burb only had 230HP with 325lbft of torque in stock form. You are pushing around a 5.5K lb vehicle then hooking up another 5K lb boat, which puts you over GVW, it's gonna struggle towing uphill. I'm guessing your turning about 2500 in OD at 65 and about 2900 in 4th with O.D. off. With the new cam and pistons and possibly an additional 75-100HP you are only talking a little over 300 HP. I would talk with some tuners and find out what chip to get with your mods.
I gave up on gas for towing several years ago, but that's another discussion altogether.

Keith
I realize this thing is no diesel, but I am getting passed by Grand Cherokees, Ford explorers, and other small Suvs that are pulling a similar boat size. Semi trucks are flying by me going up these hills. It's rather embarrassing to be honest. I remember the days when the burb was New and would pull really strong and that was back when it had 3.73 gears. With a fresh engine, better cam, and 4.56 gears, I figured this would be a great puller. It's frustrating to say the least.
 

·
Registered
Joined
·
307 Posts
I'm not sure what live data you will be able to read on an OBD1, been years since I had that scanner on my '95 Z28. But I would do as MGK has stated, and look at the fueling of the engine, injector duty cycle and pulse width and see if it's running correctly. If you don't understand what the particular PID should read/be just ask here or research online. A lot of information out there, just need to be vigilant. OBD1 isn't all that smart and won't always tell you something is wrong. Wish I could just tell you look here, just don't have the experience for that.

Keith
 

·
Registered
Joined
·
4,167 Posts
What is the fuel pressure under load? What is the idle vacuum and full load vacuum? And what is the timing curve? If you answer these, then you'll have your answer I believe.

You mentioned the scanner was reading lean under load - that's your issue almost undoubtedly, answer my questions and you'll find the answer.
 

·
Registered
Joined
·
37 Posts
Discussion Starter #17
I havent had a chance to actually hook up the scanner yet to see if it is running lean. I will this weekend and drive it up some hills and compare that to the idle specs and let you know.
Thank you!
 

·
Registered
Joined
·
245 Posts
Just remember that o2 readings should not be steady, they always vary, jumping rich then lean. Once your hooked, pull off a vacuum line momentarily to see what lean is, rich is the other way.
 

·
Registered
Joined
·
37 Posts
Discussion Starter #19
First off, I sincerely appreciate you guys for helping me out. 2nd, I dont know if the scanner tells me much. I was really hoping that it would just show lean all the way up the hill and I could chase down a new fuel pump, filter, etc., but that wasnt the case. Below are the results from the scanner. I took a bunch of recordings and included the ones that I thought would help the most. Here is what I did; I started recording when I was driving on a relatively flat road. Then I let off the gas and just let it coast in Frame 15. Frame 18 is going up a hill where I usually like to pull with medium acceleration. Frame 23 is a few seconds later when I step harder on the gas pedal and it starts to bog like it is getting too much fuel, but doesnt want to pull any harder. The last "idle" is when I got home in the driveway and just let it idle to get the baseline.
FRAME 0 = Flat Regular Driving
FRAME 15 = Coasting No Pedal
FRAME 18 = Up Hill Regular Driving
FRAME 23 = Up Hill Pedal Down
IDLE = Sitting in the driveway

FRAME 0 FRAME 15 FRAME 18 FRAME 23 IDLE
LT FUEL TRIM 118 123 121 118 127
LT FUEL TR CL 9 5 9 13 18
EVAP DUTY (%) 0 0 0 0 0
EVAP SOLENOID OFF OFF OFF OFF OFF
COOLANT 112 139 143 151 180
EGR DUTY (%) 40 40 42 48 0
EGR DUTY (%) 12 9 37 47 0
EGR VLVPOS (%) 13 8 37 46 0
EXHAUST O2 RICH RICH LEAN RICH RICH/LEAN
IAC DIRECTION REV REV REV REV REV
IAC POSITION 105 84 160 152 82
IDLE REQ (RPM) 813 775 775 763 875
INJ PW (mS) 2.7 1.4 4.4 4.5 1.3
ST FUEL TRIM 124 128 143 130 128
KNOCK RET 0 0 0 4 0
LOOP STATUS CLSD CLSD CLSD CLSD OPEN
MAP (HG) 14.28 9.05 20.60 22.45 9.05
MAP (V) 2.08 1.12 3.18 3.45 1.06
O2S (mV) 861 999 435 861 586
O2S CROSSCNTS 175 203 232 117 177
RUN TIME 1:07 2:05 2:16 2:35 4:34
TCC APPLIED NO NO NO NO NO
TCC LOCKUP NO NO NO NO NO
TCC SOLENOID OFF OFF OFF OFF OFF
THROTTLE (%) 12 0 33 42 0
TPS SENSOR (V) 1.18 .57 1.75 2.12 .57
 

·
Registered
Joined
·
245 Posts
Check your vacuum hose diagram, map Hg. Readings don't seem to match driving conditions , almost like map in hooked up to ported vacuum instead of manifold vacuum.
 
1 - 20 of 57 Posts
Top