Rebuilt motor, ran into a problem

[sschambers]

So I finished my re-build and tonight was the first night I finally got the chance to take her for a spin.
Yesterday was the first start-up. Engine sounded awesome, no problems, and it didn't even smoke one bit!

So tonight I changed the oil from the cheap non-synthetic Valvoline (used for first start-up and ran for about 45min total) to full synthetic Mobil 1 w/ Mobil 1 filter. Took it out for a drive and it drove GREAT with no problems. I went maybe 4 miles, came back to the garage to re-check for leaks and check fluids. Everything checked out 100% perfect. I started it back up and went for another drive...

Only this time I ran into a problem. It seems that when the motor is under any sort of load, it bucks/chugs/hesitates when it's still in vacuum range. I haven't even taken this motor over 3,000rpm's yet. It feels like fuel cut, or to better describe it - it feels like if I'm in 1st gear and I'm tapping the throttle quickly to make the car bounch back and forth.

To clear things up:

I DO NOT have a boost leak or a vacuum leak. I ran a boost leak test twice so far and it's perfect. I even re-checked all hoses and clamps.

Re-checked ALL plugs and wires. Plug gaps are perfect, wires are fine.

I have never had this problem prior to the engine re-build.

The chugging gets so bad, it's quite difficult to climb up the small hill that I live on.

Every single gasket, belt, O-ring, bearing, ring, clamp is NEW. There is no type of leak what-so-ever on this motor.

Also:

When I shut it off after the first time it started doing this, I went to re-start it and it started for about 2 seconds and shut itself down and threw a CEL. I don't have a code reader, I'll have to rent one from Auto Zone.

I disconnected the negative from the battery for about 10min to reset the ECU, then it started right up with no problems...until about 5 minutes later, the engine started sounding like it wanted to die. It would cut out for a split second then come back to life, at random intervals.

I thought maybe I had bad fuel because my car had been sitting in the garage since December. I chugged my way to the gas station and put $15 worth of 93oct. Chugged back to the house. I thought if it were bad gas, the new gas should help SOME. But it didn't.

Anyone else have any ideas?

 

[Calan]

Maybe a MAF or O2 sensor wiring problem?

They would both throw CEL's, and could cause problems once the ECU gets out of "startup mode" and starts adjusting fuel trims.

 

[sschambers]

Maybe a MAF or O2 sensor wiring problem?

They would both throw CEL's, and could cause problems once the ECU gets out of "startup mode" and starts adjusting fuel trims.

I tried my buddy's MAF and it did the same thing. Haven't looked too much into the O2 sensor yet.

 

[Calan]

I'd say try not to sweat it too much (if you don't have to drive the car right away), until you can get a code reader and see what that CEL is...that should point you in the right direction.

It definitely sounds like something that becomes more of a factor once the ECU starts learning. Think along those lines...I'm on 24 hours up time and too tired to think of anything other than the MAF and O2 right now though

 

[sschambers]

Thanks for the info. I'm going to rent a code reader tomorrow once Auto Zone opens up. Also, before the initial test drive, the car had warmed up for about 30 minutes and like I said the first drive was perfect with no problems.

Also, the car doesn't blow any smoke out either when it chugs. It feels like someone keeps pulling the main engine fuse out and putting it back in real fast when I'm at steady throttle. I keep thinking it's a fuel problem, myself but I'm not sure. I'm out here in the garage just scratching my head because everything is hooked up 100% correct. I'm thinking a sensor somewhere might have went bad possibly...

 

[Calan]

Couldn't hurt to pull the injectors and see if they collected some crud or something while sitting on a shelf during the build...I'm still thinking sensor or sensor wiring related though.

How do the plugs and plug wires look? Any burnt spots around the coil packs? Missing or loose ground wires?

Good luck...I'll check in tomorrow and follow along

 

[cheap90gsx]

If you put new rings in? -Fully synthetic isn't used till after the piston rings are seated. At least the first 75 miles.

 

[sschambers]

Plugs are brand new NGK's gapped at .028. I pulled 'em and they still look new. Plug wires are fine. I cleaned the injectors during the re-build and put new O-rings on them as well. When I built the motor, every single nut and bolt was torqued to proper spec and I mean EVERY nut and bolt, right down to the timing belt cover bolts...

I'm lost, I'm going to get some sleep and tear back into it tomorrow after I get the code reader.

Thanks again for the help.

 

[sschambers]

Well I found the problem.

Got the code read today at Auto Zone and it pulled the Cam Position Sensor. Bought a new one for $74.99, replaced it and haven't had the problem since!

Thanks again for the help.

Steve

 

[Calan]

Cool deal... never would have guessed it would be that sensor, but glad you got it fixed