Hard to start and rough running 1995 4.3 Blazer

[HOGEYE]

I have a 1995 Blazer. Sometimes is starts just fine and others I have to crank it a bit and it won't fire unless I hit the gas pedal. It also periodically runs a little rough once started. Sometimes it also kills right away after starting, but after I rev the engine it runs. It seems this started after I patched a large hole in the muffler. Engine has 200,000 so I don't want to put much into it. I replaced fuel pump at 130,000 and was thinking it may be the pressure regulator? I have not had it scanned and do not have a check engine light that is on.

[Hookmaster]

I had the same vehicle. The hard starting is probably the fuel pressure regulator. When it starts fine has it sat very long? Usually the longer it sits the pressurized fuel can leak back into the fuel line. The rough running may be something else. Does it rev up and down at idle. The EGR valves on these can get carboned up and stick causing this. At higher rpms they run fine. I'd change the fuel pressure regulator first and see if it solves both issues.

[MonsterMechanic]

A simple fuel pressure test will tell you if you Fuel Pressure Regulator is leaking. Or, if you do not have the tools, you can take off the Air Intake tubing and open the throttle plate by moving the throttle cable back...then you can use a small mirror and a flash light to find the Regulator inside the Intake Manifold and look for leaking fuel. The Regulator is a very common problem on these engines and the symptoms you describe fit perfectly...The hard starting and rough running.

[Jeremy airjer W]

Fuel pressure leak down test would be the first hing I did!

[deadeye]

I would do the test first too. The test saves you time and makes sure thats the problem. Once you have determined that its a fuel problem take the plenum off and do the leak test again. Then you can pinpoint where the leak is at.

I have a 95 myself and I had a problem with the pressure regulator leaking. It is a very common problem with those trucks. I ended up just getting the whole spider assembly, but motormite does make just a pressure regulator. The other problem that happens a lot is the lines inside the plenum rub on something causing a fuel leak (again motormite makes a replacement).

[HOGEYE]

How do I perform a leakdown test? Do I need to buy a special tool?

[raymondk]

i have a 94 and it seems that I have to work on it more then I drive it does it seem like it is flooded when you try to start it do you smell any gas i had the same problem the regulator leaked gas and the gas would puddle on the bottom of the plemum I would just take the top off try not to disturb the gasket if there is any gas sitting in the bottom just replace it very easy to do also since you can get at the egr valve take it out and clean any carbon and make sure that it is closed if there is any carbon wedging the valve open it will not idle hardly at all .

[deadeye]

You can get a fuel pressure tester at any auto parts store for about 20 bucks that will work perfect for that truck. It will screw into the schraeder valve (just like on your tires) on the back of the intake manifold. It is 80 bucks cheaper than paying the fee at the shop to diagnoss it and you can use it again and again.

[Scott K]

One other thing you can check, is to pull the vacuum hose off of the fuel pressure regulator and see if there is fuel in it after you shut the engine off. If there is fuel coming out of the regulator then it is bad. If there isnt then you will need a fuel pressure gauge to test it. As said it is an easy test that you should be able to do yourself.

[Jeremy airjer W]

The regulator is under the upper intake plenum on the CPI unit. There is no vacuum hose.

[Scott K]

Gotch ya!

[HOGEYE]

I took a peek inside the plenum and did notice a little fuel washing and both sides. I decided to change the plugs, wires, PCV valve and cleaned the dist cap first before pulling off the plenum. The vacume hose on the back of the plenum had a small crack whcih I also replaced. My air filter was also very dirty, which I replaced. It seems to start fine and runs better than it has in years. I will still prob put a FPR and nut kit in when I get around to it though.

[deadeye]

Ya, its one of those problems that are kind of helped with having the other stuff straight. I had my truck almost running perfect without changing the spider. I ran it for a while and it did ok, I just knew something else was off. If you do get the regulator, just make sure that there aren't any leaks somewhere else.

[mrfish1991]

Ive got a 96 s10 with the same motor

Does it seem to do a little shaking when you accel. Between 1800-2000 rpms?

Ive heard that the intakes on the 4.3s arnt the best in the world

My truck also has a bit of a hard time starting some days...but thats only when it gets realllllyyyyy cold over night

[deadeye]

The 96 has a different motor than the 95. The newer ones like yours (different injection system and phenolic upper intake) tend to have the plenum crack around the throttle body as well as the lower manifold gasket leak.

[Jeremy airjer W]

I have not had one that was cracked yet. I think you may be referring to the 3.8 plenum which would crack around the EGR port which would allow coolant to enter the intake and hydro-lock the motor as an end result.

[HOGEYE]

The truck seems to be starting and running rough again and I scanned it this am with a friends scanner and I got a P0122 code which is a low voltage to the Throttle Position Sensor. Where is the sensor located?

[Scott K]

The tp sensor is located on the drivers side of the throttle body.

[Jeremy airjer W]

the exact opposite side of where the throttle cable is connected. Some are a 3 wire flat, some are a three wire round connector.

[HOGEYE]

OK, I replaced the TP sensor and it runs a bit better. Pops right off after sitting for a bit. The Cat Converter is also sounding like a rattle box of rocks now. This whole issue started after patching a whole in the muff. I have not done a fuel pressure test yet ( I know this should have come first) but have done all the tunneup stuff (i.e. plugs, wires,cleaned cap terminals, fuel filter and egr. Battery isn't the best but is gets it started usually. When changing plugs the center plug on the passenger side was completly carboned up.

When I pulled off the control valve on the plenum I noticed a bit of fuel washing which leads me to believe I prob need a new FPR and/or nut kit. I think I also need a new CAT Converter as caused by my fuel leakage. CAT is prob at it life at 200K. I still have the hard start after it has been running with lack of power and high mileage.

[deadeye]

Ya, my truck did the same thing as that. It ended up needing a cat too. Although, with that many miles its hard to say for sure. It is worth getting fixed though. I guess its cheaper than a new truck.

That plug would be one to check again in the future. Maybe that poppet injector is goofed up, or that cylinder is where the extra fuel is dumping into. The FPR does face that way so its possible.