1991 K5 surging problem

[OSDCrusher]

My 1991 K5 Blazer has a very bad surging problem. It surges especially bad when the engine is cold. When the engine is warm it doesn't surge as bad but you can still tell it is not running right. The exhaust smells rich. If you try to drive the truck while it's surging, it will buck violently and idle extremely low, it feels like it's going to stall out at any moment. If I unplug the coolant temperature sensor and try to run the truck, it seems to run a little better when the engine is warm. The previous owner tells me he replaced the coolant temperature sensor (doesn't look all that new) and wiring harness for CTS. O2 sensor (doesn't look all that new, plug wires (look new), fuel pump (verified new), throttle body base gasket (can't tell for sure if it's new), I.A.C. valve (doesn't look all that new), T.P.S. (doesn't really look new but I don't think this has anything to do with the problem). The transmission was rebuilt with a new torque converter. Any insight on this problem would be appreciated.

[OSDCrusher]

I made a video today of the truck running: http://www.youtube.com/watch?v=I9dD5...ature=youtu.be
Disregard what I said about having gasoline in the tailpipe lol wasn't thinking straight. However, there is an abnormal amount of condensation in the tailpipe when the truck is running, and when I shut off the truck, smoke lingers out of the tailpipe. You can hear it well in the video, the idle will go from very low to very high, very low very high and it will keep doing this. Then when I rev it some, it will smooth out a bit, but still can smell gas as it's running. I took off the air cleaner assembly and looked at the fuel injectors while the engine was running, they don't seem to be spraying a cone shaped spray like they're supposed to. They dribble a bit, but not badly.
Also, I really can't drive the truck well at all. I can get it up to about 20-25 MPH then it will start bogging down and surging/falling on it's face.

[OSDCrusher]

UPDATE: Got bored today, decided to further investigate the surging problem. Unplugged MAP sensor while truck was off. Started it up and surging was gone. Idled somewhat decent (but still running rich). Went in gear fine and drove alright. When I really gave it gas, it fell on it's face and wouldn't accelerate, it sounded like it was backfiring or missing, but I can't really tell because the muffler is rusted out. I'm thinking the falling flat on it's face is because the catalytic converter is clogged? Can someone help?

[OSDCrusher]

Sorry for all these posts, but I don't see an "edit post" function. Anyhow, I just took off the EGR valve vacuum connection at the EGR valve end and plugged it with a golf tee. I started up the Blazer and it didn't stumble, but it still ran rich. What does this mean? Is the EGR valve bad?

[OSDCrusher]

Bump

[esbstuff]

I wish you luck, I have the VERY same problem!

[OSDCrusher]

Originally Posted by esbstuff

I wish you luck, I have the VERY same problem!

Thanks, I hope one of us figures out what the problem is. Seems no one knows, haven't got any responses in five days. If you figure out anything, please let me know.

[OSDCrusher]

I don't want to pay money to be able to post on an online forum. I might as well take the truck to a mechanic and pay him to figure it out, don't mean to sound rude I just don't see the point. I will check for codes tomorrow and post what I have found. Anyone have any ideas on why the unplugged MAP sensor makes the truck run better?

[OSDCrusher]

It's obvious that you don't have to pay on this from, I am not stupid. I was referring to CK5.com You have to pay just to be able to post a topic on that site.

[OSDCrusher]

This topic is clearly going nowhere. I hope an admin finds it and deletes it so I can start again or, that an admin finds it and deletes your posts. Thanks for the suggestion and everything, but I'm not paying to join a forum.

[OSDCrusher]

Bump

[OSDCrusher]

Bump, replaced MAP sensor with GM part, same problem still exists.

[68Timber]

I wish I could help. I don't know diddly about trouble-shooting these fuel injected engines. I have noticed that the EGR valve comes up as the culprit a lot. Hopefully the right person will notice this thread.

[OSDCrusher]

I came to a conclusion today that in fact, the truck IS NOT running rich, but it is running lean! The injectors look like their barely dribbling fuel while the truck is running. Also, the truck randomly stalled two times today, then took four seconds of cranking for it to start back up. The "rich" smell I thought was coming from the exhaust is the smell of a bad catalytic converter. Rotten eggs/sulfur. Looks like I will be replacing fuel pump, it sounds weak also. Finally, after I shut off the truck, I can still hear the fuel pump running for about 3 seconds and I hear fuel sloshing around in the tank even though the truck didn't move an inch.

[ChevyTech]

I agree it may be the fuel pump.
I sounds to me like it does not have good fuel pressure.
The pressure should be tested with the engine running.
Other problems can cause low fuel pressure other then a bad fuel pump. Information on this is in the threads I attached links to.

It is normal for the fuel pump to run a couple seconds after the engine is turned off.

As for the fuel noise in the tank even if you have not driven the vehicle, it could have a split hose in the tank between the pump and sending unit.

Split hose thread;
http://67-72chevytrucks.com/vboard/s...d.php?t=375132

Broken fuel pressure regulator spring thread:
http://67-72chevytrucks.com/vboard/s...d.php?t=347247

Fuel pressure testing & more thread:
http://67-72chevytrucks.com/vboard/s...d.php?t=347247

If you want to find more of my posts on TBI trucks you can search over in the 1988-1998 pickup section.

[ChevyTech]

Here is a good thread for other people with surging issues that are not from low fuel pressure. This is a four page thread that ended up being a EGR problem. There is test information for many TBI systems in this thread.

http://67-72chevytrucks.com/vboard/s...d.php?t=348308

[OSDCrusher]

ChevyTech, thanks for the always informative responses. Should I plug the MAP sensor back in and then run the truck with the EGR valve disconnected? When the MAP is unplugged, the truck runs ok, when I leave it plugged in, the surging starts again. Either way, I have to pull the tank out to fix what is going on in there and inspect everything else. I will be replacing the fuel pump, I am the third owner of the truck and the first owner did not replace it, and same with the second owner.

[ChevyTech]

You're welcome!

If you want to test the EGR you should reconnect the MAP sensor.

It is a symptom of low fuel pressure for the truck to run better with the vacuum hose to the MAP unplugged.

Your description of dribbling injectors points to a lack of fuel pressure. Your truck could also have a EGR problem, but first you should focus on the lack of a good cone shaped fuel spray pattern.

[OSDCrusher]

Ok I will reconnect MAP and then remove vacuum connection to EGR and report back. I definitely can tell that the truck has low fuel pressure and I strongly believe that there is a split hose in the fuel tank. Fuel pump sound extremely loud when I turn the key to "ON".
Also, the spray pattern from the fuel injectors is not cone shaped but rather a straight stream. Like I described before, a "dribbling" of fuel into the TB.

Thanks again.

[OSDCrusher]

ChevyTech,
Just reconnected MAP sensor and disconnected EGR valve. Immediately the surging started again. Injector spray pattern looked awful. Heard fuel spraying in the tank before starting the truck and after shutting it down.

[ChevyTech]

If when you pull the fuel pump, you can get a good photo of the hose split open, post a photo of it here in your thread.

[OSDCrusher]

Originally Posted by ChevyTech

If when you pull the fuel pump, you can get a good photo of the hose split open, post a photo of it here in your thread.

Ok, I will pull the tank within the next few weeks and I will post a picture of the split hose. Thanks for your help.

[OSDCrusher]

ChevyTech, you wouldn't happen to know what size and length fuel injection hose I would need, would you? There is an 87 Blazer fuel tank at a local junkyard with the sending unit assembly still in the tank. Would it be ok to take that fuel sending unit assembly and use it for the hose and/or pump?

[ChevyTech]

I would only use new hose.

I think it is 5/16 hose.

I suggest only using OEM (Original equipment manufacturer) fuel pumps. I have seen so many pumps from other manufactures fail in the warranty period or just after the warranty is up that I suggest only using an OEM pump.

If you are shopping around, only get an AC Delco or Delphi pump.

[OSDCrusher]

ChevyTech, I will be installing a Delphi pump. As for the 5/16 fuel hose, does it have to be submersible fuel hose or can I install regular 5/16 fuel hose?

Thank you