lunytnz

Thanks, again, for pointing out the missing rubber bumper and helping to clarify where it was supposed to be! I was able to find replacement parts at Napa (I was surprised that they are about the size of your fist). It was difficult to get the nut off the old, rusty bolt, because the OE bumper was COMPLETELY disintegrated, but I eventually prevailed. I put it to the test on a drive on a Forest Service road with big dips in the road and no problems with bottoming out the front suspension anymore. Here's a picture of the front suspension with the new rubber bumper installed. Cheers!

Thx for the picture. Before I saw it, I took this picture from the other side. Is this where the bumper should be? I presume the torsion bar is adjustable. Is that something I should look into, as well?

Thanks for calling my attention to the jounce bumper! I have the FSM, but I haven't been able to locate the bumper to make sure I'm looking at the right part. As far as I know, the bumper is original (I've owned it for over 20 years). Here's a drawing from the service manual, as well as a picture of the front suspension in my rig. Can you point out the jounce bumper? TIA!

I found that a dirty MAF was the cause of the same code and kind of runability problems in my 99. I use a K&N filter and I believe that contributed to the problem. So, now, as regular maintenance, I spray down both sides of the MAF with air intake cleaner and that has prevented any P0300 codes from recurring. I wish you luck! It can be PITA to solve these kinds of problems.

My 1999 4-door Yukon 4x4 is bottoming out the front suspension on big dips in the road. I replaced the shocks, but that wasn't enough to remedy the problem. Since this model doesn't have springs, I'm wondering if I can adjust the torsion bars in the 1999 or if I need to replace them? If I adjust the torsion bars, will it affect wheel alignment?

I have original (Bilsteins, I believe) on my 99 Yukon XLT with 4x4 (just over 200,000 miles). The ride is fine, but I feel it bottom out on big bumps. I don't have any complaints about the OEM shocks, otherwise. I do tow a snowmobile trailer from time to time. Are there any aftermarket shocks out there that have features (maybe adjustable?) that are clearly worth it and I wouldn't want to miss out on? It seems like basic gas-charged shocks will be roughly $100-125 per corner. So, $400-500 total. I doubt I would want to double that amount, though.

Where might I find a good quality replacement auto-dimming outside mirror for my 99? About 5 years ago, the auto-dimming fluid leaked out of the passenger side mirror and I found a used one at a wrecking yard and replaced just the 'mirror' part of it and it worked out well. But, now the driver side mirror has failed (leaked and now I see double when looking at the mirror) and since the truck is 20 years old, I figure it's just a matter of time before a used one will fail. I'm hoping to find a new replacement part that is both heated AND auto-dimming. I haven't had much success searching online, so hoping someone has found a good source for a quality replacement part. Ideally, JUST the mirror surface (not the entire mirror assembly, with housing/body part). Thanks for your help!

Thanks for the idea! Unfortunately, I didn't see it until after I got back from having the PCM reprogrammed. In my case, they said they believed the problem was that the PCM wasn't receiving any security message at all. Maybe your bypass approach would work in that situation... I'm not sure. Like you, I believe (based on what they told me) the change they made to the PCM resolves this problem. I'll let you know in a year or so :-) Where did you wire in the 2200 ohm resistor?

I just got it back from the shop today. After calling around to a few different places, I decided to take it to the dealership because they had the most experience with this kind of problem. As expected, they were not able to reproduce the problem in the shop. They said this was not the typical failure of the theft deterrent system. They found the same P1626 code stored, in history, as last year. The tech suspects the theft deterrent module (apparently located under the dash) is not powering up when the problem occurs. They recommended a new module, but the part is discontinued. I can find a used part, of course, but it may not be as simple as just swapping out the module (that is, the system may have to re-learn the passcode). They said they can modify the Powertrain control module (PCM) so that it will allow the engine to run if the passcode is missing (involves about one hour labor). Assuming that approach is successful, it may be the way to go if it will prevent the theft deterrent system from disabling the fuel pump AND it will work if the problem lies with the lock cylinder, Passlock module, theft deterrent module or the wiring. Anyone have thoughts or experience on modifying/reprogramming the BCM to ignore a missing passcode? Anyone replace the theft deterrent module in the middle of the dash, underneath the radio? I'm not especially concerned about someone stealing the truck with a screwdriver or the wrong key because I have an aftermarket starter interrupt device (it was in the truck when I bought it).

I had the ignition key lock cylinder replaced about 10 years ago to try to fix a similar problem. It may be time to try that again. I read somewhere that the lock cylinder can wear and tiny pieces of metal can cause problems with it working right as far as reading the key or sending the signal properly. Apparently, the BCM (body control module) is where the theft-deterrent system is located. It *could* be that, as well.

And... the answer to my big question is: in about a year! I have had no hint of any kind of problem during the past year, but today it wouldn't run again. This time I was in a campground about 20 miles from cell phone coverage. The shorter version of a MUCH longer story is that it started about 3 hours later. In the meantime, disconnecting the battery and trying my backup key made no difference. It's like the brains were temporarily scrambled in one of the computers and then, for some inexplicable reason, at some point, things get straightened out again.H Have you had to fix this problem?

Well, it's been over 2 weeks now and it's been starting and running fine, so I guess it was just a glitch in the Theft Deterrent / Security system. I'm grateful it didn't cost tons of money to fix, but don't know what else (besides a flaky connection) might have caused it. The biggest question is: when will it happen again?

Do you mean this generation of truck is notorious for having starting problems like this? What is it that fails?

The next day, when the shop tried, it started and ran just fine! It's been starting and running fine ever since. So, my suspicions about the fuel pump were wrong! The found a stored P1626 code, which means there was a communication problem between the Theft Deterrent Module and the PCM. When it doesn't receive the right password, it disables the fuel pump. When the key is turned to on, the fuel pump comes on to prime the system, so it will run for a couple of seconds, but then the PCM will turn the pump off if all is not well immediately after start. It may have just been a glitch, but now it makes me wonder. The shop tech said there could be 3-4 things that could cause the code to be set. Anyone have experience with this kind of problem and fixing it?

My 99 Yukon with Vortec 5.7L suddenly won't run. It cranks over fine, starts in about 1 second (normal), but then dies 2-3 seconds later. Giving it a little bit of throttle while starting doesn't make any difference. I was out of town when it happened, so I had to have it towed to the nearest shop. I suspect the fuel pump, but my search of the forum didn't turn up any other posts with this problem. Is this common? If not the fuel pump, any ideas what could be causing this start, but quickly dying, problem to suddenly appear? I also considered the fuel filter, but it seems unlikely it would behave this way suddenly. It's been a while, but the last time I checked the fuel pressure, it was right around 60 PSI.