B52bombardier1

Hello,

I would put this into the Conversions and Swaps area because this motor will eventually go into a Pontiac Catalina convertible but this engine is still sitting on the shop floor next to the car. The engine is a freshly rebuilt and bored .030 over, stock truck cam, 5.3-liter LM7 engine out of a 2002 Chevy Silverado that runs very nicely until it gets into Closed Loop – then the Short and Long Term Fuel Trims go crazy. The driver’s side goes rich to the point that the engine stops. The engine has great compression, no trouble codes out of the PCM at all and no oddball engine sounds. With the engine cold or warmed up, the cranking times are quite extended at 15-20 seconds before it eventually catches a good idle RPM. It seems to run better for longer with the MAF disconnected but still eventually dies the same death.

It's a stock drive by cable throttle body. All new sensors - MAP sensor, cam sensor, crank sensor, IAC sensor, TPS sensor, coolant temperature sensor and knock sensors plus their harness. It’s running a new Delphi MAF but I’ve tried three other different junk yard MAF’s with the same results and cleaned the last MAF with the specialty MAF cleaner spray. At the MAF connector, I have twelve volts and five volts at the pins and this is not a re-pinned junk yard harness. This is an all new harness from a well known vendor.

It has a solid 60 PSI of fuel pressure at the rails. I have tried several different 0411 P01 PCM tunes (12212156 and 12208322) in several different PCM’s. On the scanner, the TPS open and closed percentages track the open and closed status of the throttle plate.

The engine will accelerate by hand at the throttle valve until all four of the driver's side spark plugs load up with unburned fuel.

The MAP air pressure number is 101 kPa at key on, engine off and about 40 kPa when the engine is idling. The grams of air consumed per second at various RPM’s appears reasonable. The O2 sensors are responding but struggle to adapt. All of the driver’s side spark plugs are pig rich and wet with a sooty exhaust only on that side.

With the engine running, I think I have ruled out a vacuum leak because I have liberally sprayed the top, sides and underneath areas of the intake manifold with a flammable carb cleaner with no changes to the engine RPM.

I’ve even added length to the header pipes on each side thinking that the O2 sensors are picking up shop air and getting confused. But this was no help at all.

Any help that you can provide would be greatly appreciated.

Many thanks,

Rick

HappySalesman

iTrader: (3)

Honestly this sounds like a tune issue. You don't list any of the other mods done besides the .030 overbore. Is the rest of the motor stock?

Do you have any logs of the issue occurring? Being able to view what the sensors are reading while the issue occurs would be huge in diagnosing the problem.

Have you tried disconnecting the MAF? This would force open loop and would help narrow down the potential cause.

gametech

iTrader: (1)

Impossible for me to tell without a log to look at, but it sounds like the o2 sensors are plugged into the wrong sides of the motor.

B52bombardier1

Hello,

The .030 overbore and headers are it for engine modifications. The remainder of the motor is all stock. I'm using the stock, cleaned, impedance checked (12 ohms) and spray pattern checked and 26 pounds of fuel per hour fuel injectors with a standard truck throttle body in a standard truck intake manifold.

Tune issue? Doubtful. I have ran and I'm now running exact copies of the 12212156 and 12208322 operating system tunes that I'm running in my El Camino LM7 motor. These tunes run perfectly in my El Camino and except for the .030 overbore, these two engines are identical to each other. I've tried these two tunes in several different 0411 PCM devices all with the same driver's side results in this Catalina motor.

Logs? Not exactly. I'm using a Bluetooth OBD2 module and several different Android phone and tablet OBD2 software analysis program applications. It's not HP Tuners but the thirty or so parameter stream values that I see are all things that you would immediately recognize from HP Tuners. I'm not much familiar with HP Tuners but I can borrow the hardware from a friend if it's necessary. Basically, the engine struggles to start but then runs OK until Closed Loop where the Short and Long Term Fuel Trims go rich on the driver's side.

As noted above, yes, I have disconnected the MAF, and it does run better in Open Loop. It still struggles to start but once started, it runs better for longer but still dies a similar death.

I think I will try a different set of intake manifold gaskets tomorrow and I'm going to look more closely at the pins in the MAF connector to see if it is pinned correctly. I have already had a broken wire problem with this harness elsewhere that the vendor is sending me a new pigtail for.

Rick

B52bombardier1

Hello,

OK, O2 sensors plugged into the wrong sides of the engine. I certainly had not considered that, but I will give them a swap tomorrow. That's easy. I'd go out there and try that now, but the sound of this motor would stampede my neighbor's cows and horses this late at night.

Rick

gametech

iTrader: (1)

One other quick and easy diagnostic check is to use an infrared thermometer to check individual exhaust ports. One misfiring cylinder can also cause the trims to continue to richen until drowning the motor. You have pretty much ruled out MAF or MAP sensor issues, as these would affect the entire motor instead of just 1 bank.

B52bombardier1

Hello,

I have an infrared thermometer that can test those temperatures and can report back later. There's definitely a difference in temperature between the sides but it is not throwing any misfire codes.

Rick

B52bombardier1

Hello,

Winner, winner, chicken dinner and the big prize goes to Gametech. I swapped the O2 sensor wires and it now purrs like a kitten all the way into Closed Loop and warmed up. No smoke and it idles nicely at the commanded 650 RPM. The engine now accelerates and decelerates with ease and the passenger side stainless steel headers are taking on the same color as the drivers side. I've certainly trashed at least four spark plugs but that's nothing after solving this problem and the idling short term fuel trims settled at plus / minus three percent once it got warmed up. This has been the absolute best Fourth of July for me since losing my virginity way back in '76 on the same day and this, Gametech, is a very close second!!

It would have taken me a very long time to solve this problem and I sincerely thank you and I'd buy you that chicken dinner / prime rib / lobster / BBQ or whatever you prefer if you were closer. Now I can think about plopping this motor down into this Catalina car.

Again, many thanks,

Rick

G Atsma

I always consider Gametech our resident brain on car brains...

B52bombardier1

He is the "PCM Whisperer" in my book. It's a fine line between clever and stupid with these systems and I crossed that line. He got me back onto the good side.

Rick

G Atsma

I guess that goes both ways, as I've seen you help many fellow amateur AND pro wrenches out of jams now and then.
Love the community we have here!

gametech

iTrader: (1)

I always try to figure out what is most likely to have changed between a motor running good and not good. In this case, it was a pulled motor, which meant all of the wiring had to have been disconnected and reconnected. A wrong connection seemed much more likely than a real problem appearing for no reason. Sometimes this thought process works, and sometimes not.

RB04Av

There is a YYYYYYUUUUUUUUUUUUUJJJJJJJJJJJE wisdom in this.

There's an ancient truism that applies to inductive logic ( = I see certain things going on, certain things happening, I want to find the thing I should look at that could explain - aka that I could FIX - all these things) that never goes out of style.

"The simplest explanation that fits all the facts is most likely to be the right one."

Break it down one word at a time.

"Simplest": we're looking for ONE thing that can REALLY happen in the real world we live in. Let's leave aside alien abduction, "tolerance stackup" which ONLY occurs when there's common-cause variance like doing all the machine work on ONE machine that's not properly zeroed or the like, and so on. Look for something REALLY SIMPLE, like, the bolts weren't tightened right or the push rods were the wrong length or that sort of thing.

"Explanation": you're trying to account for what you're seeing. You propose possible causes, that maybe it's this, maybe it's that, maybe it's something else. Those are your "explanations".

"Fits": your "explanation" MUST account for your observations. No ifs, ands, buts, maybes, sometimes, or ANYTHING ELSE. If your proposed "explanation" fails to "explain" ANYTHING about what you're seeing (apart from a multiple-defects situation), then it's almost certainly WRONG.

"All": self-explanatory. All. ALL. A.L.L. If ANY of your observations refutes your proposed "explanation", or is unaccounted-for in it, then the "explanation" is almost certainly WRONG. For example: "my headlights don't work; maybe it's my ignition switch"... NO. Your headlights DON'T GO THROUGH the ign sw. YES, your ign sw might be bad; YES, you might need to change it; but it's NOT because it's making the headlights fail.

"Most likely": this truism is a "razor". it's meant to carve away extraneous bullshit. It doesn't always work perfectly; butt what it DOES do, is eliminate BULLSHIT, and give you a well-grounded starting point for your further troubleshooting. You may well find that the "most likely" "explanation" isn't "the right one"; butt if you start HERE, you'll save yourself AHELLUVALOTTA tail-chasing, sanity-doubting, hand-wringing, money-spending, time-wasting, going-in-circles MONKEY MOTION.

In the case of an engine swap, a swapped-over connection is INCREDIBLY likely. And not at all an accusation of stupidity, laziness, or even lack of attention to detail; just, a REAL EEEEEEZZZZZY thing to have accidentally happen without noticing. I'm not at all surprised that it turned out to be that.

Glad it's working right now.