GMC28

Interesting. So chase down bad connections.. ok. Would the emulator or EGR plug be the connectors I’d want to try first? no codes are thrown on my car when in limp mode… no CEL, and no codes even if i just check anyway.

Moving my issue over to this topic/string. Willys has offered some good intel, but still have my limp mode issue, which i know is an old topic. Been doing more reading, and see more causes that i need to consider. I’m not overboosting, for certain. I’ve lubed the actuator a couple of times, first time just squirting some lube in there (no luck), and 2nd time taking the linkage apart and moving the butterfly valve open/closed many dozen times, and a bunch more graphic lube. Slightly readjusted the linkage too, but i think thats a non issue as I’m certainly not over boosting. Ends up in limp mode on most drives (typical is to/from work, about 8 miles ea way, with a number of stop&goes). Sometimes it won’t go into limp mode for a whole day with several drives (start/drive/shutdown). But most often it will start off fine, will rev up, boost/mp never goes over about 190 (foot control), but then will just slip into boost mode within the first mile anyway, while keeping rpm and MP low. Tried driving it real easy when cold, or getting on it harder, just different combos to see what the cause is, but no obvious trend that i can identify. Some of the old threads on this note that the EGR plug can get moist or just be problematic, which can cause the issue apparently. I may try that… pull the plug, apply contact cleaner/dryer, and just check condition then re-plug. I did the EGR delete, and use the eastern euro chip whizmo for tricking the computer into not throwing a code, so might that unit, or the connection to that, be a cause? And with the EGR delete, would the plug I’d check be the lower plug below the turbo? (Just peeped up there last night to see a plug coming down from the wire bundle area, hard to reach, but looks like a candidate for checking) What other causes come to mind? Still wondering if the butterfly linkage is maybe just a little too sticky still, so perhaps the computer senses its not moving quick enough during normal acceleration and so goes into limp?

I do have reluctor rings ready to install, which I got I think from Glen, and maybe that’s all there is to that. I just noticed that the manual says the yellow triangle means the system can limit braking but also engine speed, which I hadn’t noticed before, so wondering if that’s related to my issue somehow.

Update: Still have the rev limiting happening intermittently. What I’ve done- finally got out to shop again and removed rear panels to access turbo linkage, and did find that it was a bit sticky. Exercised it for quite a while, used a graphite based lube (for heat), and got it moving smooth. Then it sat for a week, and on first outing it again started out ok then rev limited at about 3100. Maybe it needs even more work to make that lever smooth, but am dubious. It’s certainly not overboosting, as I’m watching closely and never see MAP above about 180-190, and it will still happen. It normally starts off on for a short distance, will rev up fine, and then suddenly it won’t. I am seeing the yellow triangle with the “!” about every 3rd time I drive, which always goes away next time I start the car. That esp mode limit fuelling, so am I perhaps having an esp issue rather than a turbo issue? for how I use the car, it’s all fine, just annoying, so will keep picking away at it. Hoping I’m missing something easy….

Wondering if i can “log” max values on the scan gauge II, to see if it does hit that overboost value now and then to kick it into limp mode. Or is that a foregone conclusion about whats happening? Again, I’ve just not seen limp mode on this car before, and had previously assumed I’d see some other indication if i was hit with it, like a warning light or something.

Gotcha. I’ve seen about 205 max, as I recall. So I can watch for over that to see if it goes into limp mode for that. I read about limp mode some years back when reading up on this forum about the car, but i never experienced it. i guess I’ll pull it apart and get a little deeper into the clean and lube.

thanks willy's- i have the scangauge2 as well, and while i can't remember why i do recall that i can't measure boost... i have the MAP reading, but not boost. installed it too long ago to remember why. Any tricks/tips on the scangauge setup as to why I can't get a boost reading?

well, more to the story... Not sure if what i did before actually helped, but after apparently addressing the rpm issue as noted above i then let it sit again for several weeks. But now after jumping in the Smart yesterday for the first time in weeks its back to showing the same bad behavior. First heading out yesterday morning it rev'd up normally for a few miles, but soon after reaching operating temperature it would no longer rev past about 3100rpm. at lunch same issue, and again last night going home. this morning it behaved normally the whole way to work, and i drove it a bit harder than i prefer, to keep pushing the RPM's up and see if it would still rev up normally, which it did, even kept working fine when fully warmed up. The "warmed up" thing may be a false lead, but i mention it as maybe there's something to that. The hot exhaust and its effect on the linkage....? I will plan to get back there and mess (move/lube) the turbo linkage again, but does this sound like its just the turbo linkage issue still? to be sure i'm clear, it hits about 3100rpm and just stops rev'ing... it doesn't slowly lose power, it just revs to that point and pretty much then its like a rev limiter comes on and pushing the throttle does nothing. hopefully just the turbo linkage and back to normal after another clean/lube but thought i'd run it up the flag pole.

all good now - lubed turbo shaft, used Napa Auto side panel/fender plastic mounting connectors for rear fender flares, and the twist lock deal that Willy's recommended was the exact unit and worked great (fyi, the '06 450 uses that twist lock that shows on ebay as being for 2007-2015 models)

Thanks all. grabbed some plastic body mounts at local auto store that I think will work. ordered that latch pin off eBay and see how it goes…

Many thanks Willy’s! the snaps I’m referring maybe are different…. The new ones would just slide into place on the fender side, into the figure eight slots, then pop into the holes on the body. Cheap, and easy, once i go get new ones. For the engine cover securing hardware, that looks right, and I’ll give it a whirl, but it says its just for later model smarts. Worth a try. Cheers

Sounds good Willys, but not even sure what to call that little piece… I’ll fumble around and figure it out. Those aren’t that unusual, just need to work out what they’re called then the web search and eBay should yield some results. Too bad about the smart junk yards, that’ll hurt in the long run. Wondering if I should try and pro-actively buy a couple items that i think i may eventually need. Bit of a crystal ball type thing, but I suppose there are a couple things on that motor that are more clearly life limited that I should consider scooping up… I would have thought a turbo would be good to have, but reading a bit on this topic on this forum i see some have replaced them and some say they tend to hold up well. May look at that some more. Did some periodic service yesterday, as the first rains in a long while came through so it was my excuse to get into the shop. Lubed up the turbo linkage as noted, and worked a charm. Cleaned, serviced, inspected things and its about ready for winter. Just need to chase down some of those plastic body “snaps” that connect the rear bumper cover/wheel well flairs to the body, which were old and broke.

Off topic from thread title, but getting into the turbo fix I see my father lost the twist lock fastener for the engine cover in the baggage area. Anyone know of an easy place to source one of those?

Hoping to get out to shop this weekend to get it lubed/freed up. interestingly the little computer plugged into OBD2 shows higher avg fuel economy than usual. Makes sense I suppose with little or no turbo boost happening. But I’ve generally always driven it “gently”, and even now up until around 2700+ on the rpm it hasn’t felt much different without the boost, so I wouldn’t have guessed the fuel economy would jump like that.

Many thanks- I’ll dig into that next weekend, and do some other annual maintenance. My father loves driving it so I don’t drive it nearly as much these days. Don’t think he even noticed any issue. cheers