2nd gen 3.0 challenge- failure code 25

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kc15842

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Guys, I just finished an engine rebuild and a manual trans swap and could use some advice. The engine starts right up and idles at ~ 1200 for the first couple minutes. It runs smooth and is very responsive with no check engine light. Than after a few minutes I get a engine light ( 25 lean) and runs rough and stumbles under load, idles nice at 800.
The air cleaner and box are all tight and I can't find any vacuum leaks. It also makes a bit of a whining noise after warmed up. Any thoughts??
 
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kc15842 said:
Guys, I just finished an engine rebuild and a manual trans swap and could use some advice. The engine starts right up and idles at ~ 1200 for the first couple minutes. It runs smooth and is very responsive with no check engine light. Than after a few minutes I get a engine light ( 25 lean) and runs rough and stumbles under load, idles nice at 800.
The air cleaner and box are all tight and I can't find any vacuum leaks. It also makes a bit of a whining noise after warmed up. Any thoughts??
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Sounds D's like heat soaked fuel injectors. Time to swap them out.
 
So far I've swapped the O2 sensor with no luck. Its odd it starts great, idles great for warm up and then like clock work the check engine light goes on and it starts running like crap.
 
It probably runs great in open loop and then once the ECU picks up O2 sensor readings, that's when it turns to crap. How did you check for vacuum leaks? They are difficult to check visually and can hide in very hard to find or seemingly insignificant places.
 
Really only did it by eye. Checked all hoses and the routing. On the intake side I secures all clamps and checked for cracks. I also tried my old K & N setup with a different VAFM. The truck ran well before the rebuild and trans swap with no issues other than being a bit tired.
 
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Your ECU may be getting a poor or non-existent signal from the O2 sensor. [MENTION=124924]mholme[/MENTION] is correct in that it's probably a closed loop issue - once the engine warms up the ECU is looking for a pulsing signal (about once/second) from the O2 sensor. If all it sees is 0 volts it assumes the mixture is too lean.

Get your engine warmed up, short TE1 to E1 in the diag connector, open the throttle to about 2000 rpm, and put a multimeter on the VF1 pin. It should oscillate from 0 to 5 volts and back about once/second. If it's stuck one way or the other (particularly if it's stuck at 0 volts), and you have a new O2 sensor, then I would double check the wiring from the O2 sensor back to the ECU.

Also check the voltage on VF1 with the jumper removed from TE1-E1. If it's at 5 volts under that condition (again, engine warmed up and running a 2000 rpm), it means the ECU is doing its best to enrich the mixture but isn't getting the results it expects.
 
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OK, tried again after cleaning the contacts so I can be sure I have good contact with my MM probes.This time I did get close to 5 v and then back to 0. Once I removed the jumper I had ~2.25 V at about the same RPM. I really don't know exactly as I don't have a portable tach unless I pull out the old tack & dwell meter.
Whats odd, I cleared the ecu this morning and had a good blinking of the engine light. I then drove the truck for about 3 miles and the light then came back on. I checked the code and now only have a 52.
It's the first time I cleared the ecu since I swapped the O2 sensor, checked and tightened all of the inlet tubing & airbox connections also reset the timing.
 
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2.25 volts w/o the jumper means the ECU is happy with the mixture. Seems like your O2 sensor loop is working OK now. (Rpm for this test isn't critical, you just want to be warmed up and well off of idle.)

The code 52 (I'm assuming that's what you meant, and it's not a transposed 25) is a knock sensor code. It doesn't mean the engine is knocking, rather it means the ECU isn't getting a signal from the knock sensor, and thus can't use that to properly adjust the timing. Instead, it will go into a limp mode with retarded timing and poor performance.

It generally means the knock sensor wiring is suspect (the sensor itself seldom fails). You might want to check the shield grounding on that wire. Part of it is buried under the plenum, so is hard to get at. Hopefully you can find the problem where the wiring from the ECU connects to the pigtail from the knock sensor.
 
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Thanks! I replaced the small wire section between the Knock Sensor and the intake during the engine build. I'll check the connection. Its funny the first few days after the initial start up I only had a 25, now a 52. I know I checked that I had a good connection between the connector back to the ECU prior to installing the engine harness. I really appreciate your help!
 
Well, I disconnected the connector at the knock sensor ohm across the pins and it was open. I checked the black wire to the ecu which is pin 5 on the small connector and I had connection. The other pin was ground, seemed like no issue as long as the sensor is working. Put it back together and no more 52 but now a 22. I'm guessing I have a wiring issue in this part of the harness. Sucks, I cant get through smog and get it registered with an engine light. I'll be chasing the 22 today.
 
I checked the connector for the temp switch and checked continuity between connector and the ecu and its good. ODD, I have 2 ecu's and with one i only get the 52 the other a 22 and 52. This is kicking my ass.
 
Could I have caused my problem with the knock sensor putting teflon sealant on the threads during assembly. That would suck.....
 
It's conceivable. If the Teflon is preventing the threads from making contact with the block, the sensor won't be able to send a signal back to the ECU.
 
I picked up a used knock sensor at the pick a part and did the remote knock sensor repair. I drilled & tapped the engine lift and torqued the KS. I used the shielded cable from my old harness, removed pin 5 from the small gray connector and inserted the remote cable. No more engine light. It runs great. Now to get to the real solution. I think my remote cable may reach the connector for the KS so I can rule out the wiring.
I have 2 ECU's one for an automatic and one for a manual trans. The one with the manual trans does not let me clear the fault codes and I always get a 22. Is there something different between the two?
 
Well, put some fresh premium gas and drove it on the freeway for about 15 miles all is good. Get to the smog station to begin the test. The tech called me over and said the engine light just went on while under load. He then visually rejects the cat as the PO welded in a bastard of a cat so he rejects it. He also rejects the remote knock sensor. I checked the code and now have a 71. Now I'll start chasing the EGR system. Looks like I'm pulling the intake and swapping KS. Damn, another $175 for a cat and $70 for an intake gasket set.
 
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