Loss of top end power

[BlazerBoyLT98]

OK here we go. 1998 Blazer LT 4 Door 4X4 W 4.3. 137K miles. Recently changed plugs, wires, cap and rotor. Changed the fuel filter about 15K miles ago and I cleaned the throttle body about 5K miles ago. I run Mobil 1 5w-30 and I ran a bottle of techtron and 93 octane through to clean a little better. Basically at 60 miles an hour or higher if I floor it or give it a good amount of gas It kind of surges up to speed. The tach will hit like 3K RPMS and then surge upwards sometimes slow and sometimes fast, almost like it is bogging down as if a carb was out of sync, I know my truck is fuel injected I have not cleaned the EGR, is that my next step? Oh and it is not throwing any codes. It was misfiring before I did the tuneup but that seemed to take care of it. Also, sometimes it starts rough like it is not getting enough gas until I give it some and then the shaking and shimmying stops and does not come back until restarted. Right before the tuneup it was running terrible, for a week after the tuneup it ran perfect, and now it is just running a little funny with the surging and with the idling rough. One more thing that has gone wrong recently is the gas gauge goes crazy sometimes and bounces all over, I have heard that could be a sign of a failing fuel pump and a bad sending unit. Thanks Everyone.

[RJ MALIBU]

sounds to me like a possible fuel pressure problem.

[MT-2500]

Originally Posted by BlazerBoyLT98

OK here we go. 1998 Blazer LT 4 Door 4X4 W 4.3. 137K miles. Recently changed plugs, wires, cap and rotor. Changed the fuel filter about 15K miles ago and I cleaned the throttle body about 5K miles ago. I run Mobil 1 5w-30 and I ran a bottle of techtron and 93 octane through to clean a little better. Basically at 60 miles an hour or higher if I floor it or give it a good amount of gas It kind of surges up to speed. The tach will hit like 3K RPMS and then surge upwards sometimes slow and sometimes fast, almost like it is bogging down as if a carb was out of sync, I know my truck is fuel injected I have not cleaned the EGR, is that my next step? Oh and it is not throwing any codes. It was misfiring before I did the tuneup but that seemed to take care of it. Also, sometimes it starts rough like it is not getting enough gas until I give it some and then the shaking and shimmying stops and does not come back until restarted. Right before the tuneup it was running terrible, for a week after the tuneup it ran perfect, and now it is just running a little funny with the surging and with the idling rough. One more thing that has gone wrong recently is the gas gauge goes crazy sometimes and bounces all over, I have heard that could be a sign of a failing fuel pump and a bad sending unit. Thanks Everyone.

Here is a good thing to check or a place to start..
Hard to start cold or lose of power.
Check cold start fuel pressure.
Check engine running fuel pressure.
Check engine running on the road fuel pressure.
Then shut it off and watch for fast leak down.
Pinch off at rubber part or block off return line and check full pressure.
Later V6 and V8 gm engines should have 60-66 fuel pressure.
Cold start should be 64-65 lbs of pressure.
If you do not have full fuel pressure on a cold start the injectors will not squirt fuel.
Do not leave home without it.
Engine running should be 60-66 lbs pressure depending on engine load.
Full pressure with return pinched off should be 75-85 or more.
And if it has a fast leak down after shut off you have a leak.
Post back fuel pressure readings.
MT

[BlazerBoyLT98]

I can try that, not sure when but soon. Would loss of fuel pressure throw a SES? Thanks by the way

[MT-2500]

Originally Posted by BlazerBoyLT98

I can try that, not sure when but soon. Would loss of fuel pressure throw a SES? Thanks by the way

No it will not set any direct codes.
The computer has no way to tell what the fuel pressure is.
But fuel trim and other senser reading may point to low fuel pressure.
MT

[BlazerLT]

Sounds normal to me.

This engine doesn't start to produce power until after 3000rpms.

The air resistance at that speed is what is holding it back.

WEith my CPI, when I hit 3000rpms and the IMTV valve kicks in, it is like a mini-turbo spooled up and the engine really takes off.

[BlazerBoyLT98]

But it never did this before.

Originally Posted by BlazerLT

Sounds normal to me.

This engine doesn't start to produce power until after 3000rpms.

The air resistance at that speed is what is holding it back.

WEith my CPI, when I hit 3000rpms and the IMTV valve kicks in, it is like a mini-turbo spooled up and the engine really takes off.

[horse482]

What brand of spark plugs did you put in the blazer?

[BlazerBoyLT98]

AC Delco Plats all the way

[BlazerLT]

Have you lately reoiled your air filter?

[BlazerBoyLT98]

Begining of last summer

[muddog321]

Info I've read on fuel pressure was minimum 60 psi cold start and 54 running.
If the gauge is bad time to change the pump anyway (1 piece on these). As above on oiling, clean the MAF sensor. Rough idle can be caused by injection poppet problems. If this does not occur while reving while parked, what about the trans converter slipping.

[BlazerLT]

Originally Posted by BlazerBoyLT98

Begining of last summer

I would clean your MAF again.

Sounds like it is not able to detect the air flow at higher rpms.

[BlazerBoyLT98]

Would make sense. I may have over oiled the filter, so I let it sit in the sun for a while the other day and now it looks like it did when I first got it. I will clean the MAF again. Thanks

[BlazerLT]

Remember to use brake cleaner and a gentle toothbrush.

Be REALLY gentle and massage the gunk off the filament wires.