Fired 'er up for the first time, but...

[adz]

I finished up the '99 LQ4 today in my blazer. It ran great the first few times I started it up. I let it warm up for at least 10 minutes and then revved it up a little. It sounded great, ran smooth and quiet. Then I took it out for a test drive and it was gutless. It almost immediately started running like it was running a cylinder or two short (vibration, no power, etc.). Then I slowly let it accelerate, and it would just hit a flat spot at about 3/4 throttle. I turned it around and took it back. By the time I got it back it was running even rougher, and when I'd give it a little bit of gas it'd knock (like a pinging).

I freaked, but now that I've given it some thought I think it must not be getting enough fuel, or fuel pressure. I did only have a gallon or two of gas in the tank, could this be a factor? (I don't think so)

I installed a tank with fuel pump from a 96+ tahoe (I think) that I found at a local wrecking yard. I'm starting to wonder if it might have been a 95 (it had the 95+ interior) and so not enough fuel pressure. I guess my next step is to check fuel pressure, but can someone tell me if I'm barking up the wrong tree?

Thanks!

[RedHeartbeat]

Fuel pressure or water temp. Did you have a water temp guage installed, a manual one? You may have air in the top end and it was overheating.

[1BADC10]

<div class='quotetop'>QUOTE(RedHeartbeat &#064; May 12 2007, 11&#58;43 PM) [snapback]93254[/snapback]</div>

Did you have a water temp guage installed, a manual one? You may have air in the top end and it was overheating.
[/b]

Based on the performance description, that would be my guess.

[adz]

Yes, I have an aftermarket Autometer water temp gauge and sensor which I installed into the head (I iinstalled it where the allen head bolt on the rear of the passenger side head used to be). It was running in the 170-180 range the whole time.

<div class='quotetop'>QUOTE(RedHeartbeat &#064; May 12 2007, 09&#58;43 PM) [snapback]93254[/snapback]</div>

Fuel pressure or water temp. Did you have a water temp guage installed, a manual one? You may have air in the top end and it was overheating.
[/b]

<div class='quotetop'>QUOTE(1BADC10 &#064; May 13 2007, 08&#58;23 PM) [snapback]93326[/snapback]</div>

Based on the performance description, that would be my guess.
[/b]

[adz]

Just checked the fuel pressure at the rail. 35psi. I&#39;m going to go get a new fuel filter (should have replaced it in the first place) to be sure it isn&#39;t holding me back, then I&#39;ll pull the tank. Anyone have any other thoughts on why my fuel pressure is low?

[RedHeartbeat]

ruptured fuel line connecting the fuel pump to the steel line coming out of the tank. It will happen every time when you use poor quality hose to join the two parts together. Get a good piece of fuel injection quality 3/8" hose and four hose clamps. Double clamp each end of the hose onto its respective part.

[adz]

I was thinking that might be it since that tank had sat dry in the wrecking yard for who-knows-how-long. I didn&#39;t open the tank since the tahoe it was in was in good shape.

I&#39;ll let you know what I find, but do you think running at 35psi would make it run that crappy?

[RedHeartbeat]

Absolutely will make it run like crap.

[adz]

Ok, I checked the line in the tank, it&#39;s ok. Nothing is clogged. I think I got the wrong tank/pump. I just went and got the AC/Delco EP381 pump. It looks exactly like the old one I have... It&#39;s rated pretty high. We&#39;ll see how it works. (crossing fingers)

[RedHeartbeat]

All the pumps look the same, pretty much. It&#39;s what&#39;s inside that counts. A high pressure pump usually has a lot more vanes visible from the bottom, than a lower pressure pump.