sdg2844

Hi all! My husband inherited his dad's 1991 Stepside a few years ago when he passed.

The truck had a new GM Motor put in it probably about 15 years ago and has 80k miles.

honestly, the truck has been great and reliable for the past few years since we've had it. However, it now has a small issue where it has a hesitation when starting from idle, like at a stop sign, and a rough, uneven idle until it warms up.

we have a close family friend who has done most of the work on the truck throughout its lifetime, and also owns a 1991 C1500 with the same problem. We also had another mechanic who devoted himself exclusively to classic cars/trucks check it out, and have done the usual: Spark plugs, rotors, etc.

general consensus at this point is it's definitely not the engine, which is great news. We did have the EGR valve replaced, which helped a LITTLE, but not entirely. Both our family friend and the other mechanic believe it probably centers around the emissions system, and specifically the vacuum control module.

sounds like we could leave it and simply put up with it, but I'm a techie, so I'm interested in whether there is a software update that is obtainable on a vacuum control module or on the main computer (whatever that might be in a 1991 truck), of that age? I can see some third party sellers who have flashed swap-out control units, but that makes me itchy, as that could go one way or the other and end up being a real problem. In other words, sometimes less is more!

just wondering if anyone out there has intimate experience with this model/year truck and/or their specific issue, and can shed any futher light or offer advice?

we did stop by our local Chevy dealer, who we have been pretty happy with over the years, and they do often work on older cars. They won't commit to whether or not software updates are available on a truck this old, but likely not. But they can do their own diagnosis on the issue for $250. Not sure whether it's worth it when we've had 2 other mechanics already take a look, but would love to hear thoughts on dealer work or get advice on mechanics or specific dealers in NorCal who might be the best options to help.

any thoughts or advice welcome!

jfmorris

Unfortunately I cannot shed light on the problem, but I have a 1996 stepside myself that I've held onto all these years, even with a newer truck, because I love that body style.

The computer on the 1991 is going to use ODB1. 1996 and later use ODB2, and very few shops still carry the code reader for the older style cars, but if you can find someone who has one, it *should* provide some guidance on the issue. I came across this list of ODB1 codes for the 1995 and earlier GM vehicles:

https://www.gmtruckclub.com/threads/...d-older.30334/

Before I paid the dealer anything, I would find out if they have the diagnostic tools to connect to the vehicle. Otherwise they are just guessing like the first two mechanics.

sdg2844

Thanks for the reply. Yeah, my husband loves the body style too.

And we did end up taking it to our local dealer who has one old-timer left.

at this point, they are pretty sure that it is a valve or cam issue... so... an engine misfire! 😔

They advised us to find a mechanic who has an oscilloscope to test that theory. They no longer do, and said if they did a compression test, it'd cost about $750 to probably find out it's the engine. Oscilloscope would cost more like $100.

so, at least they are being straight with us here!

We're both thinking that it's time to let the old girl go in peace. Sadly, this is her second engine which has about 80k miles. Genuine GM... but... oh well.

jfmorris

Sorry to hear that. I'm on the opposite side of things. 1996 step side and starting a restoration project, with the goal being to sell my 2006 Silverado to pay for new paint and upholstery on the 1996. The '96 has 201,500 miles on it, with the original engine and transmission, and at the moment my biggest mechanical issue is the AC won't hold a charge, and leaks down a week or two after I charge it. The peeling clear coat paint and ripped up drivers seat make it look like a dog too, but that's all cosmetic. I'm at the point where I figure that the truck hasn't had a payment in 24 years, even if I end up doing a transmission rebuild or engine rebuild, its not the end of the world if I like the truck. I've seen these old body styles in full restored condition going for $20-30,000 dollars online. But they looked a lot better than mine!

Here's hoping the o-scope test is negative, although that won't help, as then you are still stuck with the mystery problem...

sdg2844

Hah! We are at the opposite end of the spectrum. Ironically, the truck just smogged successfully about 2 months ago, which is crazy, considering nobody thinks it should. My father-in-law had the truck repainted, maroon, same color as before, probably 15 or so years ago now, but didn't have a clearcoat put on it. And it always looks dusty and has suffered for not having one. We have a new dashboard we were going to put in it, that we got for a great price, and were thinking of adding a rack and different tonneau cover... f-in-law was a painter, my husband is in lumber, and needs it to haul wood, if he's going to keep it, so we were planning some changes. But with some small ticket items and this probable engine issue, by the time we fixed it up to where it should be, we'd probably have spent about $20k to get there. My husband likes the idea of restoring old trucks, but doesn't really have the time, and has the need for something that he drives maybe once/week, for hauling projects. So we're probably going to upgrade to a newer Silverado crew cab 6 1/2 ft bed, maybe 2017 or so, with 50k-ish miles on it... which you can do for about 30k, here in CA. Just hope we don't inherit any new problems by doing that. Of course, I want to get a new Tacoma... but I can appreciate my husband needs a slightly beefier truck for his needs, and I rarely drive it anyway.

jfmorris

Good luck!

I think the problem with newer Toyotas is no V8 option anymore, which could be an issue for hauling. I read about lots of issues with the newer Silverado's since 2021 and the supply chain shortages, but think anything in the 2017-2019 range should be reliable. But it will cost you more than replacing the engine AND transmission in the 1991, haha...