I didn't take any pictures when I did my spider replacement...

Here are the pics from the manual with the upper plenum off:


The first manual pic above doesn't show the #1 and #6 fuel lines & poppet nozzles for some reason...

The original SCFI system has 6 electronic injectors located in a central pack which are fired sequentially, feeding fuel to pressure actuated poppet nozzles located in the intake runners directly ahead of the intake valves. These poppet nozzles can gum up over time, causing problems.

In mid-02, GM released an updated version, the MFI system, when they did some more tweaks to the 4.3L engine. Below is a picture of a v8 MFI spider assembly (v6 assembly is very similar less 2 injectors).

Courtesy of Lindertech.com

The MFI spider is an upgrade in the sense that the often problematic poppet nozzles are gone, moving the electronic injectors out of the injector pack to the ports. The MFI spider is backwards compatible in all '96 thru mid-'02 SCFI motors (the only motors available in the Blazer in this time period) although the '96 thru '98 may require a different injector pack mount. One thing to note is that the MFI system cannot flow as much fuel as the older SCFI system can which may present a problem if you are planning on pushing the limits of your motor through upgrades.

 

Thanks for all of that.

I must say, that is a very unique design. It would be easy to hide a nitrous system!

That's all for now. We'll be replacing the fuel filter Thursday night and redoing the tests.
I'll (we'll) post up the results.

 

Update: The fuel filter was changed on thrusday night. That solved the problem big time. Obviously the pump is still whining but its' a stronger sounding whine now..like it's flowing more fuel. Pressure stays solid and all the power is back to the motor!

That's the good news...

The bad news is friday morning when i went to start the truck i heard a loud clicking coming from the engine bay, audible in the cabin. Sounded like it could be lifters so i checked the oil...was a bit low so i topped up. No change. Had to leave so i shut if off and took the girlfriend's car. Get back yesterday, turn the motor on...same clicking...decide to let engine warm up... clicking gets softer. Eventually at running temp you can only hear the clicking from under the motor..thinking now maybe exhaust leak? Anyways, dont' drive anywhere, shut it off...start it this morning... fainting clicking can be heard from underneath but that's it...drive about 10 minutes to restaraunt for breakfast. After 1/2 breakfast, turn truck on, loud clicking heard in cabin... turn truck off, back on same thing. Drive slowly... lots of hesitation... coast home at 40kms...about to pull in driveway notice clicking gone... go for short drive..power back, no clicking. Fill tank up with gas(it was almost empty) and drive home...no issues.

So..i have no idea ... but i'm guessing it's something in teh fuel system? Perhaps air in the system from the filter swap? The odd time at idle it seems to surge.. and the odd time you hear a sound I can best describe as fuel 'sloshing' somewhere up front.

Any ideas??

 

That sucks that you couldn't take the truck Friday.

There wont be any air in the fuel line. It's not a closed system like brake hydraulics, or clutch, so any air would have been purged
when we fired up the truck.

It's odd that the engine would develop a ticking sound the day after the fuel filter swap. I can't see how it would be related, but
anything is possible? We'll have a look under the hood in case I dislodged a vacuum line while connecting the fuel pressure gauge.

Other than that, we can scan the port and see if anything else developed over night (weird).

 

Unless you are continuously getting air in the fuel lines, air isn't the problem. All of the air would be purged on initial start up after the filter replacement.

Ticking would either be a VERY violent misfire, an exhaust leak, or an oil supply problem. You really need to narrow that selection down for us... A misfire of that magnitude would cause a check engine light. An exhaust leak could cause the engine to run rich which could explain the loss of power, but not the random nature of the problem as you described it. An oil supply issue should have resulted in a hard part failure if it was bad enough to cause a loss of power...

 

Thanks for the feedback guys...i really dont' know what it is. I had it out last night taking the gf to dinner and it ran fine. Then this morning coming into work it ran fine. Could bad gas cause this? (although the first half of that last tank seemed okay). I filled up yesterday and since then it's not made the noise, nor have i experienced any loss in power.

There have been no check engine or code lights.

I guess i'll keep an eye on it... proceed with the plugs and wires replacement and if it acts up again, scan it and go from there.

 

Update: Been okay until this morning. Drove in to work fine but right when i got there, i thought i heard a clicking sound and then the heat stopped working and my vents were blowing cold air??? Leaving work this afternoon the heat was back on... but i noticed a slight shudder in low rpm acceleration, fine as i got into it. At one point heat stopped working again..but came back on minutes later. Then driving through a large snow/slush puddle i came out of it with a check engine light on.

So now i'm wondering if it's electrical?? The fuel pump seemed to waiver a bit more through all this... so it could either be going or somethign electrical is getting in the way?

Man, this truck seems to ahve some gremlins. I'm hoping to get the code scanned tonight and i'll post up what the result is.

 

Okay so i'm driving into work today and it's driving fine... check engine light still on, didn't get a chance to scan it last night. Then after a few mins it starts to studder again in the low rpm's... feels like a miss. So i'm wondering now ... maybea burnt wire? I smelled something melty in teh engine bay when i got to work, but coudln't look at it with my work clothes on. I wonder if it starts misfiring when it gets hot? Misfiring can cause a code right? Hope to get it scanned tonight, or tomorrow at the latest, only driving to and from work in the meantime.

 

Yes, a misfire can cause a code, but a misfire typically is accompanied by a flashing check engine light.

Check the codes and let us know.

 

I had my 1997 blazer fuel pump replaced about a month ago, then it went out again. I exchanged it for a new one, that one last about 5 minutes and it made a deep growl type noise when the key was turned. I bought a dealer GM pump the 3rd time, but when it was put in, there seemed to be no power going to the pump. The relay clicks, as it should and the fuses are fine. The 12 volt supply wire that supplys power to the pump has hardly any power at all. A friend of mine tested it with a light tester and it was a very dim light. He also checked the wires on the underside by the drivers door in the harness and there is no power in the hot wire. I don't even know where to begin to try and figure out what to do next? What do I check? I'm lost! I hope someone can help.