need help with my dd ASAP!

[99_2door]

i picked up an 89 k5 for a winter dd (116k miles, no rust, really nice shape) and after having it a couple weeks its developed a problem that is driving me crazy. i know its not a tahoe but i figured theres some current or former owners in here....at least i hope! everything was fine until i started it up one time and it was surging at idle. just figured it was cold (and 21 years old) and started driving anyway. i made it about a mile before it was surging and trying to die. had to keep revving it at stop signs and even driving along it was cutting out pretty bad. ended up shutting off so i pulled off the road and let it sit for a few minutes. restarted it and everything was good for a few more blocks and then it went crazy again. limped it home and replaced the IAC valve. instantly fixed it or so i thought until a couple days later it went nuts again. got codes 34 (map sensor) and 44 (o2 sensor). i just put a new map sensor in and no improvements. when i unplug the connector to the map sensor it idles and drives perfectly. i drove it that way to the dealer to have them smoke test the vacuum lines and everything checked out....no vacuum leaks anywhere. they pressure tested the fuel system and said it was good but wanted to keep it overnight. well this morning i get a call that its definitely the fuel pump in their opinion. they hooked up the fuel pressure tester again and when it was going crazy they said it was low fuel pressure. i know the pumps are notorious for killing themselves in these trucks but i dont get it......at full throttle it runs great and with the connector to the map sensor unplugged (closed loop?) it runs fine. but when everything is connected the fuel pump is bad? but only sometimes?! WTF is going on here.
any help or advice is greatly appreciated!!!!!!!!!!!!!
i'm going to pick up the blazer right now and bring it home because they want $1100 to do a fuel pump
my plan when i get home is change the o2 sensor (already have one) and see what happens. what else could it be? i've got a fuel filter to put on. also thinking about doing a tps sensor and a coolant sensor. any other things i should be looking at? i just don't understand how a fuel pump would act like that plus i'm not looking forward to swapping it in the freezing cold right now. i shipped the blazer from california to the midwest but being fuel injected i dont think that really makes a difference? could an o2 sensor being bad really have that big of an effect? and only intermittently?
thanks in advance!

 

[Diller]

Ok, I may be able to help. I have owned 4 K5s (87, 88, 90, 91 - all fuel injected). Try replacing the throttle body base gasket. It sits right below the throttle body. At idle, it may be sucking in extra air, thus throwing off how the truck runs. At WOT (wide open throttle), it will also be sucking in extra air, but will be dumping more fuel due to throttle position. With the added air and fuel, your mixture will be much closer to correct, allowing the truck to run smoother.

Another problem I've seen would be the EGR valve. Try unplugging the vacuum line and plug it with a golf tee. Drive the truck to see if your drivability improves. If so, replace the valve.


Diller
'99 Yukon SLT
'08 Hummer H3

 

[grimm]

You'd be surprised how big of an effect a bad o2 sensor can have. I'd say replace it since you have a new one already. Afterwards, fire it up and see how it runs. If no changes, take Diller's advice and go from there. Good luck.

 

[99_2door]

thanks for the quick help guys. i just drove it home from the dealer and it was running great. i wish it was just something constant that could be identified!

diller, thanks for the tip. that definitely makes sense with regard to the tb gasket but wouldnt that have shown up on the vacuum leak test? i forgot to mention that i have an egr valve to put in but i tested the one on the motor now and it was fine. probably wouldnt hurt to replace it considering its most likely the original one.

grimm, i am going to swap the o2 sensor tomorrow morning and see what happens. this is the first tbi motor i've played with so its kinda new to me. i guess that o2 sensor code is there for a reason but i've had a hard time believing thats my main problem. i had an 01 mustang with no cats and removed two of the four o2 sensors and never had a problem like this.

 

[longstand]

i dont have cat-converter or 02 Sensor my truck Runs Great.

For the Fuel Pump. it dont cost Over $100 to replace.
i got my fuel pump from ebay new for less than $100. and it works perfect.
and its kinda hard to replace them if you dont know what you are doing "" LIKE ME ".

I say. Do the SeaFoam Treatment on your Engine before you replace the 02 Sensor.

Sea-foam will clean your engine great, i did it all on my SUV and cars, even my Hybrid and it work perfect. and if you don't believe me, after your Sea-Foam treatment remove your intake manifold and see how clean it is VS not using the sea-foam


Change the Fuel PUMP.. and Fuel Filter. if your TRUCK/SUV is that OLD. just REPLACE IT.. its cheap..$80 at EBAY.com

 

[grimm]

Had a bad o2 sensor in my RX-7, caused a ******/sporadic idle. Guess it depends on the vehicle.

I think its probably still a good idea to install the new o2 sensor. Even if its not causing the problem you're experiencing, you did get an o2 sensor code, which might mean its bad anyways, and at the very least, that could hurt your gas mileage a bit. Wouldn't hurt to install a new fuel filter as well. Heard many stories of problems caused by a simple fuel filter. Seafoam probably wouldn't hurt either. Once again, Good Luck!

 

[99Yuk]

I'm sorry that I don't have anything constructive to help you with, but Damn! That's a fine looking truck! Love those rims!

GL on the hunt.

 

[99_2door]

i've never tried seafoam before but i guess i could do that. and i'm definitely going to change the fuel filter tomorrow morning.

99Yuk i figured i would throw a few more pics up for you. the other day was the first snow i think its ever seen! other than this issue i'm having, i've been real happy with the k5. its a pretty fun winter beater and for what i paid i couldnt pass it up.

 

[grimm]

Yeah, I'm with 99Yuk : That's a bad-ass, awesome lookin' truck man. I've always been fond of the K5s. Hope you get your problems solved with it.

 

[96ProCompTahoe]

Yeah, I'm with 99Yuk : That's a bad-ass, awesome lookin' truck man. I've always been fond of the K5s. Hope you get your problems solved with it.

x2

looks like its in ridiculously good shape