I did post up a question the other day about my problems with this engine but after driving it some more I realised I got the symptoms almost exactly wrong. Here goes attempt two...

Startup is FINE, no problems. Seems to Idle OKish in P/N but stumbles with a misfire in gear when standing still.

The misfire is intermitent but seems to come fairly consitantly after pulling away from a set of lights. Opening the throttle HELPS and the misfire clears and the truck takes off.

I've done some readng about the CPI system - the regulator to be specific. I'm wondering if thats leaking and flooding a cylinder? Opening the thottle gets a rush of air in there weakening the mixture to a point it can fire.

Apparently the electrical system has had plugs & wires done already. They do look pretty fresh I have to say.

I was going to check the plenum for the "cleaning" associated with the regulator leak - shall I go ahead or am I barking up the wrong tree?

Many thanks in advance,

Dan

 

Hi Dan,
Im new here and I have a 98, so I dont know how helpful my suggestions will be but here goes.

The first places that I would look at are the IAC valve and the EGR valve. It sounds like you might have either a stuck closed IAC valve or an EGR valve that is sticking open. I have never had either go bad on my 4.3L, but I am pretty sure the intake manifold+TB design is different after 96 or 97. Others will probably know if these are common problems for your year or not. Is the SES light on? For a 94 you should be able to do the paper-clip trick to get the codes out. If no SES light, take the air pipe off, open the butterfly with your hand and shine a bright flash light into the manifold. If you see shiny metal, then there is probably fuel leaking in there. If you see heavy deposits then the EGR is probably sticking. If it is just flat black and smooth surfaces, then it is fine. You can remove the IAC (Idle Air Control) valve and motor from the TB and with it still plugged into the harness have a friend key the ignition, NOT START IT. The shaft should move. Depending on the exact design it may shoot out, so keep your hand over the little shaft and spring. If it doesnt move, then that is probably your problem. If it does shoot out, you should be able to work it back in with some oil and patience. Again someone with more experience will know if you will encounter this. Check the IAC passageways for deposits. Clean out if needed. I have used drill bits and a trimmed down copper pipe fitting brush for this. Dont use a drill, just your fingers to turn the bit or a brush.

Only once did I have a IAC valve mounting screw gall the threads in the TB of a different engine, but BOY O BOY what a pain that was to deal with on a Saturday afternoon. If either of the screws isnt turning easily with a L shaped allen or torx driver, then go to the junk yard and pick up a complete TB to have on hand if you accidentally break off a screw or rip out the threads. If they come out easy, then you have a spare IAC valve attached to your shinny new TB. If not, then you have to pull the TB to drill, tap, hcoil the hole anyway.

Good Luck,
-William

 

I just did the diagnosis as described in this thread - https://blazerforum.com/forum/tech-articles-diy-29/diy-fuel-pressure-regulator-blazer-4-3l-cpi-engine-37510/

Both removing the air flow regulator and looking through the throttle body show generally black drivers side plenum runners and goldish tan colour on the passenger side.

The actual TB opening was also a goldish colour also.

I think this sounds like a fuel leak of somesort but some further guidence would be appreciated.

I think IAC stuck closed would cause stalling, this is deffinately not a stall but a misfire. The EGR I'm not sure - could it still be that?

Dan

 

What is the fuel pressure & leak down? 1st place to start before anything else.

 

That I don't know I don't have a pressure gauge. Does the goldish colour not indicate a leak though?

 

Well I just whipped the upper plenum off. Its actually leaking on the Drivers Side! The back wall where the fuel lines enter the plenum is perfectly, eat your dinner off of it clean.

There was a pretty big puddle of fuel when I opened it. I dried it all out and cranked it with no spark and although difficuilt to actually see it drip down there, it soon became damp and a little puddle apeared once again.

 

Well your right in there you might want to replace the wiring that hooks to the spider , i guess its a common problem. I just had to change mine today . The fuel pump was working and I had fuel right to the spider and everytime i took it apart it would work so I put it back together and it would work for a while then act up again .

 

I had the same problem with mine drove me crazy

 

Just wondering what problems were caused by having bad wiring going to the spider injector?

 

Random hesitation, no starts, etc. Replace the connector and see. It isn't that expensive.