4.3w low power

[5693dtcd]

Hello- I have a 2000 Blazer with 123,000 miles. It currently has very low power. I cannot get any acceleration out of it. The exhaust sounds like the engine is running against itself. I have been struggling with this for a year now. I do most of my own work.
At first I thought the exhaust was plugged. Midas put on a new convertor and muffler. No change. The plugs, wires, cap and rotor are new.
I then broke down and took it to a dealer. They said the exhaust is plugged. I took it back to Midas. Put a 2nd convertor and muffler on.
No change.
Tried to go on vacation pulling a smal camper- Problem got worse. Had another GM dealer look at it - could not determine problem.
No check engine light.
Since then I have-
Installed new intake gaskets
New fuel filter
New fuel pump
New timing chain
Tried a used ignition module,coil,and fuel injection spider.
All of these did nothing. The fuel spider actually made it worse.
I have had it hooked up to a Snap On computer. All the sensors appear to be doing what they are supposed to.
The problem is in the timing. At idle it is 20 BTDC. Try to throttle up and it starts to advance but when the engine hits around 3000 rpm the timing retards to less than 10. The timing is not advancing like it should. The knock sensor and MAP sensors are both creating the proper voltage signal to the ECM. Shop floor no load RPM's rarely get over 3500. When they do the timing is not retarding as far. What else can affect timing?
This is my first posting. I have been able to try other ideas that I have seen posted here on this web sight.
Thank you for reading.

[MT-2500]

Check engine vacuum at idle and at 2K rpm and post back vacuum readings.
What were the camshaft retard readings on the scanner?
How is the fuel pressure?

[AJT1961]

If you ever find the cause, PLEASE make sure to post the fix. I also have a 2000 Blazer (125,000 miles) that suffers from relatively low power despite more-or-less everything being new AC Delco parts, good oil and fuel pressure and no codes whatsoever. I can live with mine, but I know the power is not nearly what it should be, and I wouldn't even try to tow with it. I have been monitoring the board for quite a while now, and it seems that there is some problem peculiar to 2000 Blazers that causes this problem -- although I've never seen a solution. Whenever I have seen a "low power" post with no other problems, more often than not it seems to involve a 2000. A somewhat odd sidenote -- a little while after I replaced my lower intake gasket, I ran a quart of block flushing solvent in the crankcase for the recommended number of minutes, drained it and put in fresh oil and filter. During the test drive, it rode like I had installed a supercharger on the vehicle -- the increase in power was beyond incredible -- it seemed even better than when I bought it new. After that, the power gradually decreased over a few hundred miles and went back to "normal" since then, which was over a year ago. I've always changed the oil and filter every 3000 miles from new, so I assumed it was not a general sludge problem. I don't know what any of this means (is there some offending senser that the block flush temporarily cleaned?), or whether it could be related to the problem you are having. But anyway, good luck finding your problem.

[need_a_new_truck]

Did you have the problem before you installed new intake gaskets?

[AJT1961]

Yes.

[5693dtcd]

Originally Posted by MT-2500

Check engine vacuum at idle and at 2K rpm and post back vacuum readings.
What were the camshaft retard readings on the scanner?
How is the fuel pressure?

Thank you for responding.

I do not have a vacuum gauge. The MAP readings on the scanner are
10.7" HG at idle
1.36 V at idle
8.9" HG at 2000 RPM
1.0 V at 2000 RPM
As long as the MAP sensor is good these readings should be accurate. Should this be confirmed with a gauge connected directly to the manifold?
Camshaft retard is at -11 degrees both at idle and 2000 rpm.
Fuel psi is 60 psi peaking at 65. I installed a new fuel pump and inline filter. The reading had been 55 psi. The new pump made no change at all in the power.
I work in parts at a medium duty GM dealer. Some of the techs at work thinks it is the injectors. They test good on the scanner. I realize this only checks them electronically. It would not detect a bad spray pattern or uneven fuel delivery. I tried a used fuel injector spider but who knows how long it had sit or how many miles were on it. I may try a new one this weekend. Has anyone changed them and how many miles did you have on the truck? Did you gain power?

[5693dtcd]

Thank you for responding. The problem did exist before I changed the intake manifold gaskets. Even though I could not find an exhaust leak( by spraying carb cleaner around manifold) I was at wits end. The old gaskets looked good coming off. The new ones did not make it better.
I have been working this problem fo a long time. I am starting to suspect the injectors more and more. (see other reply) I have a friend with a 2000 Blazer with this same problem. A lot of people I talk to though say this 4.3 L is a good little powerful engine. Mine used to be.

[AJT1961]

>>Has anyone changed them and how many miles did you have on the truck? Did you gain power?<<

I replaced the OEM spider in my 2000 (currently 125,000 miles) with the recommended replacement GM unit about 10 months ago. My old unit's pressure regulator was leaking down causing hard starts. It solved the hard starting problem, but did nothing whatsoever to improve the low power problem. I am thinking about replacing the Oxygen sensors (mine have never been replaced) even though I am getting no codes and it passes emissions easily. Have you tried replacing your O2 sensors?

[MT-2500]

Originally Posted by 5693dtcd

Thank you for responding.

I do not have a vacuum gauge. The MAP readings on the scanner are
10.7" HG at idle
1.36 V at idle
8.9" HG at 2000 RPM
1.0 V at 2000 RPM
As long as the MAP sensor is good these readings should be accurate. Should this be confirmed with a gauge connected directly to the manifold?
Camshaft retard is at -11 degrees both at idle and 2000 rpm.
Fuel psi is 60 psi peaking at 65. I installed a new fuel pump and inline filter. The reading had been 55 psi. The new pump made no change at all in the power.
I work in parts at a medium duty GM dealer. Some of the techs at work thinks it is the injectors. They test good on the scanner. I realize this only checks them electronically. It would not detect a bad spray pattern or uneven fuel delivery. I tried a used fuel injector spider but who knows how long it had sit or how many miles were on it. I may try a new one this weekend. Has anyone changed them and how many miles did you have on the truck? Did you gain power?

The vacuum gauge check test for restricted exhaust system.
You can pickup a vacuum gauge at parts place or tool dealer cheap.
One of the first and cheapest test tools made.

Yor camshaft retard reading/setting is bad.
You need to bring it in as close to 0 degress as you can.
Shoulds not be over -2 or + 2 degrees at the most.

If the no adjustable dist and off 11 degres you may have to remove dist and turn the dist gear a half turn to get it back in.
Rebuilt or exchange dist sometimes the gear not timed/set right.
A half turn will change it around 10 to 12 degrees.
http://files.automotiveforums.com/ga...hp?photo=51302

[MT-2500]

Unless you are on top of a mountain 10 in hg maf sensor reading is not good.
What is you sea level altitude?
Do you have any fuel trim short or long term readings?

In. hg at 2000 ft should be around 28 in. hg and 29 at 1000 ft.

[blazes9395]

Originally Posted by MT-2500

Yor camshaft retard reading/setting is bad.
You need to bring it in as close to 0 degress as you can.
Shoulds not be over -2 or + 2 degrees at the most.

If the no adjustable dist and off 11 degres you may have to remove dist and turn the dist gear a half turn to get it back in.
Rebuilt or exchange dist sometimes the gear not timed/set right.
A half turn will change it around 10 to 12 degrees.
http://files.automotiveforums.com/ga...hp?photo=51302

This IS a big problem, you may have found your problem. My opinion, you need to get this figured out. Follow MT instructions, half turn and get it dialed in to the proper settings and go from there.

[5693dtcd]

Hello- No, I have not tried to replace the O2 sensor. They have passed and are fluxuating like they should. With the reply concerning the cam retard it looks like I beeter look at the distributor again. (see other replies) Thanks for your response.

[5693dtcd]

The distributor is fixed. I have taken it out but I was very careful to put it back in where it came out. I will investigate further though. The GM tech that worked on it earlier this summer told me about a reference point on the dist. There is a small 6 and 8 cast into the housing of the dist. On a 6 cyl with #1 at TDC the rotor should point at the 6- likewise on an 8 cyl.
Thanks for your reply.
According to the local airport we are at 597 feet above sea level.

[5693dtcd]

I have removed the distributor but was aware of engine position and TDC. I will inspect the drive gear. Could it be wore out? I tried a used dist. out of an engine that had blown. Now that I've typed this it makes me wonder it the dist. was bad in this engine and he just drove it till it blew!

[5693dtcd]

Thanks for the bulletin. That is very helpful. I am confident that the exhaust is not restricted.
The original dist. is in the truck now. I started having this problem before I removed it. I remove it to try a different cam position sensor.
Thanks for your reply- I've got some things to check out.