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andydew
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DDR , I need your help:

A buddy and I are working on his 2000 gmc Yukon ( suburban)

His rear main seal was leaking, along with a few other problems. We have pulled the motor and fixed everything, put it back together, and Houston, we have a problem...

First, we noticed the transmission indicator in the dash doesn't identify which gear it's in; when the key is first turned on, it says its in prk for 3 seconds, and then the highlighted square disappears.

Second, we noticed it doesn't start; it doesn't crank a single bit. When the key is turned, the starter does nothing, not even a click. We have checked the starter, and it is fine.

We guessed that the module on the side of the trans was the trans positioning sensor, and that it was defective, so we replaced that, but no luck. We went over all the connections, and everything looks fine. I'm thinking the two issues are directly related, but I'd appreciate any advice or suggestions as my buddy needs this vehicle in a bad way.

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I would think that the ppps on the side of the tranz had the electrical dissconnect from it ? that module may require replacment along with the harness connector w/ pigtail (DEALER PARTS ONLY) ...Def start there...Also make sure you did not pich the harness between the bellhousing and the block.. ;)

Edited by SAND~~SNAKE
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Definetly didn't get pinched. He said they struggled with it coming apart. Maybe a problem with the pigtail. We found a new pigtail at O'rielys. We are gonna head there now and try that. There's a four wire and a 7 wire connector. O'rielys has the seven, so we'll start there.

Thanks SS

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That pigtail/ connector is glued into the switch from the factory. Not sure why but it makes it nearly impossible to unplug without destroying the wiring. I would pay close attention to the wiring and terminals in the connector. I'm sure there is probably a bad connection there because of this. We remove the bolts that attach it to the trans and slide the switch off the selector shaft as the bolts loosen to prevent dealing with this situation. Then just make sure you adjust it properly so it corresponds correctly with the shifter position.

Good luck!

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It can be tuned out. At this point its probably about fixed though. I know when I have dealt with it, I used the alignment tool when putting it together on the side of the trans. The dash lights should come on either way, and if you get it in nuetral (indicated) it should turn over. If it doesnt there may be another problem.

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Didn't get the pigtail after all... We'll try again next weekend :(

Thanks for the replies; re confirmed what we were guessing. We thought someone else had glued in the pigtail though... Never would've guessed government motors did that nonsense at the factory. A buddy said he had wrenched on the pigtail a bit to get it apart, so more than likely the damage was done then; so a simple wiring job and we'll be up and running. My pals Yukon has 240k, and a leaking rear main seal was all it needed. I just hope once we get it back together, it holds out for him ;p

Thanks again! I'll get out a victory post once we are up and running!!

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Well, the 7 wire pigtail O'Rielleys sold us was the wrong one, so he picked up the right pigtails at the delaership. He got it wired up and, whalla, she fired right up, and the indicator works, but still does not show the park position...Is that just a matter of an adjustment? eitherway, that solved our not starting problem. Glitch #2 is when we fire it up, the oil pressure hits 20-40, then back to 0. We've shut it off each time. The oil level is full, with a new filter, and no leaks...I'm thinkin a bad sensor, or perhaps something foreign is getting sucked up in the pump. The problem repeats evry time we try.

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New problem....just a matter of seconds and it drops. It is consistently doing the same thing... Thinking about hooking up a manual gauge to verify its really at zero; not sure where to hook one up if we go that route?

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Pulled the pan today; found nothing remarkable. There was a lot of grit/grime in the pan... Considering it had just been wiped clean, but figured we aggitated that loose with the work that was done...don't believe that'd plug the pickup tube.

We're wondering if maybe it's a bad sensor? Any suggestions?

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I have heard it run , but shutting it off as soon as the oil pressure hits zero, I really haven't noticed any substantial valve train noise... What would be the fix if that's the problem?

I'm doing a little wrench work on it, and another buddy, a jet mechanic for the Air Force, is wrenching too, but neither of us are comfortably knowledgable about this particular motor, so any details are much appreciated. We are trying to help out the Yukons owner, a buddy trying to make ends meet. We all appreciate your insight!!!

Edited by andydew
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The most common real oil pressure problem is caused by damage to the o ring on the pick up tube that slides into the pump. Some people pinch them, sometimes they forget them, sometimes they put one on the tube when theres already one in the pump. Pretty common on cam swaps.

If you pulled the pick up off.....(you did if you did bearings) then I d look there if I thought it was real. For the record, ive never seen a sensor do that. It either worked or didnt at all.

Edited by 1320
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I thought for sure it was a plug... i expected to find a piece of gasket/ foreign material stuck on the oil pick up tube inlet, But no there was nothing. If it were the O ring, do the symptoms match ? It does build oil pressure for a few seconds before dropping to zero... One time it held oil pressure for about 20 seconds before dropping back to zero. I would think if it were the O-ring it would never develop pressure at all, But I will have my Air Force buddy check for it Nonetheless.. We are doing the work on the Yukon at his house out in Hemet; I only get out there to help on the weekends, But I'm relaying any advice to them everyday. As for the sensor we are basically out of ideas... Starting to wonder if the oil pressure is actually fine but getting a false read due to electrical Issues? Maybe a bad sensor or a bad connection somewhere?

If it were that bypass relief valve what is the fix? Is that a part that can be replaced Exclusively, Or would you replace the entire oil pump...?

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I've never seen a split o-ring on the pickup. You might want to verify the connector and wiring at the sender (behind the intake manifold) didn't get damage during the process). Those senders go bad alot but they usually either peg full high or don't register at all.

The only way I know of to actually check the oil pressure is to use a GM specific tool/ adapter that screw in place of the oil filter so you can check the pressure with a gauge.

If it was a stuck bypass/ relief valve, you would replace the oil pump. The valve rides in an aluminum bore or small cylinder inside the oil pump and they stick sometimes. But for it to build pressure then dump off, that doesn't sound like a possibility.

Let it idle for a few minutes with "no oil pressure". See if the lifters begin to make noise. This may be a sender or wiring issue. Make sure all your grounds are good and that no wires got pinched back there.

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I d probably start it....listen for noise and maybe rev it up and see if the gauge responds. You can drill a 1/8 pipe hole in the aluminum block above the oil filter to get a mechanicl gauge on it. It probably has the cooler though and that makes it tougher.

It is common to damage the sensor on the firewall.... on install or removal.

You could just take the sensor out.....unplug the coil packs, and spin it over....and put your thumb over the hole. If it makes a mess....its probably ok.

Pete, a lot of people pinch the o ring....half on the tube and half on the outside edge. It happens mostly when people do cam swaps and leave the pan and pick up in place. Its a tight squeeze to get the pump back on and in the pick up thats mounted still. I d think in this case its pretty unlikely cause the pick up was off, and they could see the install easy.

Edited by 1320
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Pete, a lot of people pinch the o ring....half on the tube and half on the outside edge. It happens mostly when people do cam swaps and leave the pan and pick up in place. Its a tight squeeze to get the pump back on and in the pick up thats mounted still. I d think in this case its pretty unlikely cause the pick up was off, and they could see the install easy.

I'm sure they do, but it's just nothing I have ever seen in my experiences. ;)

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you probably never stick wooden dowel rods in either......when swapping cams, you can try to just stick the lifters up, or dowel rod it and catch the lifter oil groove edge, so none fall as you carefully slide one out and the other in, that way no pulling heads.

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Ok....We pulled the oil pressure sender, and noticed it was leaking oil into the wiring pigtail( probably bumped during engine removal/install) we changed out the sensor, and whalllaaaa! We have oil pressure...at elevated rpms...but as soon as we let it idle, the pressure drops to zero, and we do noticed some shreaking squeals, and possibly some lifter/valve train noise. The needle bops to zero and the DIC check oil pressure warning comes on. No leaks; Everything else is normal.

Wondering if that sounds like an O ring on the pickup tube not sealing properly, or an oil pump, or ???

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...but as soon as we let it idle, the pressure drops to zero, and we do noticed some shreaking squeals, and possibly some lifter/valve train noise.

Squeals? :unsure: Is there any run time on this motor after repairing it? What exactly was done to the motor when it was out?

Were any abrasive disks used when cleaning the engine?

If the pickup tube was pulled then I would definitely check that first if you think it has an oil pressure issue. Curious what exactly was done though first.

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It was removed primarily to replace a rear main seal. When out, they did a tune up, new rear seal, pan seal, and when it was reinstalled, I discovered a leaking water pump. We got that replaced, and when we tried to start it, we encountered our first issue: the trans selector module. We fixed yhat, but Then when we started it, we had the oil pressure drop. We dropped the pan looking for foreign material in the pickup tube, so we had it out to clean it( but did not replace the Oring).Now, with a new pressure sensor, it's showing pressure, just not at idle. We let it run at 2k Rpms for 5-10 min, and all seems fine, but the pressure drops to zero at idle.

(No abrasives were used. I believe they tried to de sludge it before diassembly with s store bought additive.)

now reassembled and topped off with synthetic, When it idles is when it makes abnormal noise, like a metal on metal shreaking sound, making us believe its truly not getting oil at low rpms

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? did you have the pick up off when you did the rear main seal? If not, and you had no pressure then, its probably not the oring in the pick up to pump connection.

It was off after though>....? right to check for debris in the tube? The oring either stays on the tube or stays in the pump. Ask and see if they remember seeing it. They dont ussually get damaged unless the tube is installed wrong, then they leak. It sounds pretty bad....

Was the rear cover removed were the rear main installs? Just curious...Was it changed to a different one?

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To the best of my knowledge the inlet tube was not removed doing the rear seal. It was not removed until I went over there trying to help troubleshoot . The o ring is accounted for and intact on the end of that inlet tube; I suspect that O-ring was flattened out and hardened to the point that it is not sealing on reassembly, Causing the oil pump to suck air at low RPM instead of oil, Due to lower suction at lower RPM...

Is this a plausible theory, or would you recommend looking at Replacing the oil pump, or???

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