My daughter had a freind replace the fuel pump on her '96 or '97 Blazer 4.3Liter. She has not been able to drive the vehicle since. The car starts and immediately goes to the red line on the tach, then begins to die, if you keep pumping the gaspedalit will run but never gets to a point where it will idle.

I have a sneaky suspicion that a o-ring is missing that holds the fuel lines to theintake manifold, she said she saw it drop into the engine and the guy couldn't find it. Would this cause such a problem? What else would cause the engine to run at high rpm's and not idle properly.
It has a brand new fuel pump and fuel filter.

One other thing that comes to mind is the trottle positioning sensor. Could this be bad?

 

I re-read this after I sent it, the o-ring did not fall into the engine but down between the firewall and tranny. I guess what I'm asking is...If the o-ring is missing, could this suck air into the fuel system and cause it to idle very high?

 

You have a stuck throttle. Check the cables at the throttle body. They must have been improperly installed. The fuel pump is attatched to the gas tank at the back of the vehicle. Replacing it does not really require any work to be done near the engine...maybe the depressurization of the system, or the disconnection of the battery...but that's it. Most likely he replaced something else like the fuel spider which requires the removal of the throttle body and would allow for the mishap.

Do not start the truck and allow it to redline for an extended period of time (we're talking 5 seconds max)...especially if it's going into the red. You'll blow your engine doing that.

If what you're describing is consistent with what's really going on though, then the throttle must be stuck open in order to let air into the system....whether it's at the throttle body itself or not is something you or your mechanic must figure out.

A shop manual such as Hayne's or Chiltons would be handy in this situation and can be purchased at any respectable auto parts store.

 

Thanks for the reply "wisdomracing"....I am certain that the problem is NOT a stuck accelerator. After the engine runs a few seconds at very high idle it begins to die and by pumping the excellerator it will keep it running. My daughter said the guy who replaced the fuel pump took the fuel lines off near the throttle body and got sprayed in the face with gas, I guess that was his way of checking for fuel pressure[:@]. She also said the o-ring or 2 fell while he was doing this. I was just wondering if he did not replace these o-ring would it have anything to do with the high idle, (it doesn't actually red-line but comes very close).

I can work the throttle from under the hood while she starts the car and if it were a stuck throttle I would see and/or feel that.

Any other suggestions?

 

Is the check engine light coming on? It could be a disconnected sensor which the computer is compesating for by raising the idle. Go through some of the harnesses and look for loose/missing connections.

Also, while the engine is running, check the injector body (between the firewall and throttle body) where the fuel lines connect to it. These are the ones he got sprayed in the face by. If there are missing o-rings, it's almost a guarantee that fuel will be leaking (more like spraying) while the engine is running...trust me I just went through this last night/this morning. This could again cause the engine to compensate by raising the idle. If this is the case, go to a dealership and buy there o-ring kit for this (GM# 17113205). It cost me $38 w/tax and comes with an assortment of o-rings, spacers and such. You will only need a select few. While you're there, ask them to print out a blown up diagram of the spider injector to assist in putting it back together. It sure helped me.

 

Fuel leaks should not lead to increased idle. Sounds to me like there is a fairly large vacuum leak. The component requiring the largest vacuum source is the brake booster. Follow the vacuum line from the booster to the intake manifold and see if it is disconnected. The next thing to check would be that the PCV hose/valve is installed correctly both in the driver's side valve cover and on the intake manifold.

What else did this 'mechanic' have apart under the hood when he was 'replacing the fuel pump'?

 

Great, This gives me something to move forward with. I will try these things out. Do you know why there is o-rings and spacers, why not just 2 orings? Maybe there is some intricate channels for the gas and air to mix....Nah, that shouldn't happen until it gets to the throttle body. I just wonder if this guy put these orings and spacers in the wrong order.

Thanks for the help, I will try these soon, have some other things to catch up on before I get back to her Blazer.

 

Thanks for your input,

I will check for vacuum leaks, I checked once but only in the vacinity of the throttle body. I have no Idea what other things the 'mechanic' took apart, other than the fuel pump and these fuel lines. I know he charged my daughter a great deal of $$$ for the fuel pump and miscellaneous parts.

 

I am sorry to hear that.. Sounds like he was messing around with things that he shouldn't have been. Unless he replaced the intake manifold gaskets and/or injection spider, there is no reason to be removing the fuel lines.

The o-rings and spacers that Wisdom was speaking of are where the fuel lines go into the injection spider as shown in the picture below:


If you have no fuel leaks now, there shouldn't be a problem with the fuel system. I am really leaning towards a vacuum leak.

Is this something that just started recently or has it always done this since the mechanic worked on it?

 

I haven't noticed any gas leaking. This all started from what was believed to be a bad fuel pump. The car would only run when gas was poured into the throttle body. This fellow replaced the fuel pump and wasable to get it running but only under extremely high RPM's. I think at some point he pulled the fuel lines to see if the pressure was up (probably did not have a pressure gage). This is when my daughter noticed the orings dropping down near the firewall.

The guy spent several days trying to get it running afterwards, but finally gave up.
This is where I take over, but until now I had no idea of where to start.

One more question...The throttle positioning sensor....Does this only sense the position of the throttle or does it have some control over the throttle. In otherwords could the TPS cause the high RPM's

As you cansee I'm grabbing at straws, I may have to eventually break down and have her take it to a shop.

Ayear or two ago I replaced her intake manifold, she had a gasket leaking anti-freeze out the back of the engine. Couldn't really find the leak until I took it apart, only saw puddles.