OK... crappy isn't a great description. I have been going through one thing after another. Replaced plugs, dist cap, rotor and wires, fuel filter as well. My 4.3 starts fine, idles only slightly rough..about 1/4 throttle and it misses badly...open wide and it smooths out. I had my local shop scan it and the sensors all checked out OK. I tested the fuel pressure and am getting a bit over 55 psi. So, next thing will be looking inside the plenum. I am starting to think the fuel pressure regulator or spider.

Any thoughts? I confess that I am rather a newbie with these new fangled CMFI systems...I have always been a carburetor kind of guy. I have spent hours digging through the forum posts and haven't found a description that sounds like my problem.

 

If you really think its a fuel problem, and it could very well be just that, go through the fuel system diagnostic sticky...55psi, is that when you turn the key on? Its a little low...what does fuel pressure do while its running?
I had sort of a similar issue, and it turned out to be a crankshaft position sensor throwing timing off, but if you have had it checked it could be fuel. How did your spark plugs look? Have you cleaned your IAC or MAF sensor? Might be worth pulling your EGR valve and cleaning that up too...somplace to start anyway!

 

Did the fuel pressure bleed off? If so, the most likely culprit is the FPR.

If it holds steady, I would look elsewhere. Check the MAP sensor for proper operation per the procedure below:

 

Further to my post....OK, I have the plenum cover removed and surprise surprise...it looks just like the photo posted somewhere on this forum. Nice clean and goldish colour on the passenger side and carbon on the driver side. Now,a beer and I shall pressure it up and see what leak shows up.

I think that I managed to insert a photo....after about a half hour the fuel pressure dropped to 40 psi

 

That doesn't look all that bad. Typically you can see fresh aluminum where the leak is and there would be pooled fuel in the lower portions of the manifold.

Let us know if you see a leak if you pressurize the system with the plenum off.

 

Also make sure the EGR valve gasket is on correctly, aligned and all that. This will cause rough idle, rough running a low speeds and then fine at highway speeds. Just wonder how I know this!!

 

Well...got it all back together and ran perfect...no happy dance though. Headed to work this morning and barely got a block. Back to missing badly and jerking....got home and it died in the driveway, then stalled and would not start. Managed to push it to the side of the road and take the spare car. I have replaced distributor, rotor, wires, plugs, checked fuel pressure (60 lbs), replaced the plenum cover gasket, checked EGR and replaced that gasket. It fired up and ran beautifully yesterdaym drove all over town for a couple of hours. This morning, back to the same old crappy running. So...I suppose I need to go over the crank/cam position sensors and MAP sensor. Where are they on a 95 4.3? I am waiting for a code reader I ordered to arrive. I can take it to a shop, but they all want $65+ to read the codes, and $114.00 at the dealer to update them. Everything has a price tag these days....the mechanic (sorry technician) farts and another $50 goes on the bill.

 

I almost gurantee it's that EGR vlave pintle sticking and carboned up.

 

My 95 did that every so often and it was a piece of carbon stuck in the EGR valve but it also lit up the service engine soon light. If the EGR valve is partially open its getting too much "preburned" air/gas to idle right but at some point the EGR valve opens on up and the engine is then getting the right amount of already burned air.

May not be your problem, just thought I'd mention it.

 

The '95 does not have a crank position sensor.

I still say it is the EGR valve....piece of carbon holding it open when it should be shut. My 95 did this a couple of times.