Suburban Driveability/Starting issues

[biggsteve97]

I am working on a 99 old body Suburban with the 5.7L Vortec and about a month ago or so fuel mileage started to drop. Went from 600-700 per tank to 275-350 per tank currently, started running extremely rough and surges at idle, also developed a hard start condition. Just put a new cap,rotor, wires, plugs, air filter, and fuel filter about 6 months ago. About a week ago it would not start all. The ignition coil turned out to be bad and the passenger side primary oxygen sensor was bad. Replaced both the coil and the primary sensors, the engine started right up and ran great for 4 days then started running rough and surging as well as the SES light started to flash. 5 of the spark plugs were covered with ash and burnt. Replaced all the plugs and the engine started right up ran great for 8 days. Then Monday morning it would not start, no cough, no sputter, no attempt to start just as before. Tried for about an hour then suddenly it just started, it ran rough but no surging and no SES light. I have 55-60 psi fuel pressure, good spark, good compression, no vacuum leaks unless the plastic manifold is cracked internally. I am at a loss. I do not have access to a live data reader to see if any sensors are just not reading. The no start only happens after it has sat overnight. For over a year the engine also has had a problem revving up over 4300 rpm at wide open throttle. It bogs down and refuses to rev any higher but it you back out of the throttle half way it will rev up to about 5000rpm then it shifts but it has no power. It ran great otherwise if you never needed to pass anyone. Before I put the oxygen sensors in the engine would not rev up past 3800 at wide open throttle.

[biggsteve97]

Update: I pulled the fuel filter tonight to make sure it wasnt plugged and it was good. However after putting everything back together I checked the fuel pressure and on the first turn of the key it didnt get over 10psi, on the second turn it didnt get over 30psi, but on the third cycle of they key it topped out at 55 psi. Then engine started right up but when i tried to rev the engine the fuel pressure dropped to 50 psi, engine bogged, i heard a pop from the intake then the engine died. when i started it back up the fuel pressure was 60 psi and reved up strong. took it for a drive and ran great.

[bwood]

How many miles? The low and inconsistant fuel pressure is a concern. A failing fuel pressure regulator can be working you over. It is mounted under the upper intake on the passenger side of the injector assy. It can also leak fuel into the intake runners just below it, which if memory serves me, are for cylinders #6 & #8. This will soot up those plugs. It can be identified by a clean spot where the fuel has washed away the buildup.

[biggsteve97]

Originally Posted by bwood

How many miles? The low and inconsistant fuel pressure is a concern. A failing fuel pressure regulator can be working you over. It is mounted under the upper intake on the passenger side of the injector assy. It can also leak fuel into the intake runners just below it, which if memory serves me, are for cylinders #6 & #8. This will soot up those plugs. It can be identified by a clean spot where the fuel has washed away the buildup.

im not sure exactly but it is around 150,000 miles. Its not mine im just working on it for a friend. She told me last night that after I put the new plugs and the oxygen sensors in it has been running great it just is hard to start cold. I was suspecting the pressure regulator but have conflicting information as to its location. The soot was on 5 of the 8 plugs i contributed that mostly to the bad oxygen sensors, one of them was plugged up, but I may have to pull the upper intake and check for leaks. Until last night, every time i have checked the fuel pressure when running it was 55 psi, cranking pressure was about 53psi. the damn thing always starts when I go to work on it so it makes it difficult to figure out. After the pop sound from the intake cranking pressure was 63 psi and running pressure was 60 psi. This makes me believe the problem is inside the intake but I am not certain and dont want to just throw parts it.

[bwood]

The fuel pressure regulator is on the injector assy on this generation of Vortec engines. If you look at the top of the intake, you will see two steel lines on the passenger side of the intake. This is the supply and return fuel lines. Just to the passneger side of the two lines is a large square electrical connector, this is the top of the injector assy. Just to the passenger side of the connector, under the upper intake, is the fuel pressure regulator. I will hunt up some pics or a thread or something that better illustrates this.

[bwood]

Newer style MPFI injector assy:

This is of new, out of the box assy. The regulator is the goldish piece.


Here is a MPFI assy installed, the regulator is circled:

[biggsteve97]

Originally Posted by bwood

Newer style MPFI injector assy:

This is of new, out of the box assy. The regulator is the goldish piece.


Here is a MPFI assy installed, the regulator is circled:

no pictures came through. Well on this engine the fuel lines are on the drivers side and they enter the intake just in front and to the drivers side of the throttle body however I do not remember any electrical connectors anywhere around them. I do believe the regulator is on the the spider assembly though since I was unable to locate it anywhere else. I just hope that is the problem, I am going to try and pull the upper intake tomorrow evening and see what I find.

[bwood]

Originally Posted by biggsteve97

Well on this engine the fuel lines are on the drivers side and they enter the intake just in front and to the drivers side of the throttle body however I do not remember any electrical connectors anywhere around them. I do believe the regulator is on the the spider assembly though since I was unable to locate it anywhere else. I just hope that is the problem, I am going to try and pull the upper intake tomorrow evening and see what I find.

I did screw up, the fuel lines are on the drivers side. The connector I'm talking about is about 3"x4", black/smooth with the wires coming from the back and has the 16 injector connections in it. The pics come up on both of my PCs, I'm not sure why you can't see them.

[biggsteve97]

Would anyone know the process in which to pull the upper intake and replace the spider?

[tommie]

http://67-72chevytrucks.com/vboard/s...d.php?t=497523

replacing the spider injector assembly is very easy to do... was not a hard job to do....

[biggsteve97]

I thought it wouldnt be too bad just time consuming. I just wanted to make sure there where not special torque sequences for the upper manifold before I dive into the repair this morning. Thanks for the info.