I'm hoping to get a bit of feedback on this issue cause it has me baffled. Blazer ran fine before I did this repairwork. Not sure if it's another problem that showed itself after the repair, or if it's something I overlooked. 1995 blazer with 4.3 vortec.

I read about the fuel leak problem on here and decided to check into it since the exhaust and engine constantly smelled of fuel when I ran it. I took off the upper plenum and found the fuel pressure regulator was leaking badly. Fixed that easily with a new one. I put everything back together with a new gasket. Checked and re-checked all the connections. Now it's idling rough and hesitates when I give it gas while driving.

It's already had new plugs, wires, cap, rotor replaced. Fuel and air filter new. I don't have a fuel pressure tester to check that. No vacuum leaks that I can find. No CEL on dash. EGR valve also replaced with screen in gasket. Good flow from the exhaust too. Other than possible fuel pressure being too low, or an emissions component, I don't know what else could be causing this issue. Like I said, it ran better before I fixed the leak lol

If, being a newbie to the forum, I posted in the wrong section I do apologise in advance. Any suggestions or advice would be greatly appreciated.

 

Time to plunk down the $30 for a fuel pressure tester. If you moved around the spider too much, you likely opened up a leak on the 'nut kit' (internal fuel lines).

 

Possibly, but I don't believe so. After changing the regulator, I ran the fuel pump several times and made sure there were no other leaks before I put the plenum back on. I've got a buddy who does mechanic work. I'll see if he has a tester. If not, then it's off to auto zone. =)

 

Take a real good look at your EGR valve gasket and ensure that it did not slip to one side when you installed it. Also did you clean the EGR when you had it off? Possible that a chunk of carbon is keeping the valve open at all times in which would make the idle rough and cause hesitation

 

Did you replace the injector harness inside the plenum when you had it apart? Sometimes the contacts get weak and cause an intermittent connection/condition.

 

Problem solved! Turns out it was the MAP sensor. I did check fuel pressure just to be sure. I'm getting 65 psi at KOEO. Well within specs if not better. I did get worried after I took the tester off the schrader valve though. (I only hand tightened the tester as instructed.) Valve started leaking like crazy. I guess it had never been used. I took it off and played around with it till I got it to seat properly again. Runs like a dream. Thanks for the input. =)

 

How did you determine that it was the MAP sensor? I also have a similar rough idle, not horrible, just enough to hear it and feel it. I just replaced the spider and fuel lines due to a FPR leak. The slight rough idle is about the same now as before I replaced the spider. No CEL codes or problems with emission testing.

JB

 

You can test the MAP sensor output using a multimeter & back probing the connection. I have posted the values in another thread. A search for "map+test+altitude" should turn up the relevant details.

 

I finally got around to testing the MAP. To test the sensor, I followed the information from a previuous post about "map sensor altitude". With the sensor green wire backprobed, and black ground also I got a value of 4.9 V. I'm at sea level so that is in the range of 3.8 to 5.5 V. I also attached a handheld vacuum pump and applied 10 in vacuum and the voltage dropped to 2.9. This was again in the range. This made it seem the sensor was ok.

I then followed another test (outlined in Haynes manual) where the sensor is back in place on the manifold, but the voltmeter is still connected to the sensor. Started engine and got a reading of 1.8 V. Manual says 1.5 to volts is ok. Revved the engine to 1000 rpm and the reading went down to 1.2 V. Revved up to 2000 rpm and the reading went even lower to 0.98 V. According to the manual, the voltage reading should be going up with engine speed.

Does this indicate that the MAP sensor is bad or do I have a vacuum problem? Thanks.

JB