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Motor Home Engine Problems?

Tiny
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  • MEMBER
  • 1997 CHEVROLET VAN
  • 7.4L
  • V8
  • 2WD
  • AUTOMATIC
  • 99,000 MILES
The coach is a 1997 Adventurer the engine is Chevy 454 7.4 L Vortec block with 95,000 original miles I live in it, having an issue that might be a blown head gasket or worse and I really need to deal with it before the next bad storm that may force us to evacuate. Check Engine light not on, can't run OBD2 says its either not connected or the ignition is not on, first thing thar comes to mind is bad EGR, bad ECM? Bad Sensors? First noticeable symptom is white smoke from the manifold, no trace of sweet smell, I took video of it I'm trying to figure out how to share it (no smoke or sweet smell from rear exhaust, only droplets of water, (moisture in the fuel lines is common here, I add a bottle of heat and seams to keep it in check) 2nd is had a back fire 1x but started up rough, high idle to almost stall till it warms up than it revs high and then adjusts to close to normal idle. It hasn't had a tune up in years, there is a presence of oil on the engine cover spark plugs manifold side. No sign of coolant leak, I did the trick to take the coolant cap off before starting and as soon as I started it in less than a minute it overflowed bubbling, I understand that could be a sign of a blown head gasket. Any thoughts on what's going on and what I can do to prevent any potential further damage? Thanks
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Friday, May 5th, 2023 AT 9:37 PM

19 Replies

Tiny
STEVE W.
  • MECHANIC
  • 13,015 POSTS
It sounds like a bad gasket. You could try one of these tests to verify the problem. That engine is normally very reliable, but they can still fail.

https://www.2carpros.com/articles/head-gasket-blown-test

You can get the test gear as loaner tools. The fastest one is to use the cooling system pressure tester in a backwards way. Start with a cold engine, put the pressure tester on the radiator. Now start the engine and watch the gauge. If it starts to rise rapidly without the temperature gauge showing much of a rise the pressure is coming from somewhere and a bad head gasket would be a likely bet. I would start with the pressure test and then work from there.
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Saturday, May 6th, 2023 AT 12:00 AM
Tiny
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Thanks, I will look for it and test. Could the high idle symptoms be related? I just read on the link, that the test for the bubbles in radiator needs to be done with the engine cool, does that mean not running? If so, does that mean I did the test wrong? Thanks
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Saturday, May 6th, 2023 AT 7:19 AM
Tiny
STEVE W.
  • MECHANIC
  • 13,015 POSTS
The engine needs to be running but you do the test at the first start of the day or after the engine has sat a while, so the coolant is cool. So, you remove the cap when it's been setting for a while, then start the engine and watch for bubbles.
High idle could be from a vacuum leak which could cause it to run lean and get hot faster because of it but we need to try to verify if there is a worse problem first.
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Saturday, May 6th, 2023 AT 7:33 AM
Tiny
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Okay, I understand, I should have mentioned I can hear vacuum like sounds like air is being sucked in from somewhere, for what it's worth it has cruise control. I checked for voltage on the ECM fuse and I'm getting 12 volts I think I was able to run a OBD2 scan, I took some photos of the results and will upload them as I can, although one does say fail the component ID $0c indicates a misfire but that is all the info I could find for that. I jumped the gun and yesterday I added some Bar's Leaks High Mileage Engine Repair. I hope it's not too late and the head gasket doesn't have to be replaced I know it can be a somewhat labored job and I'm not about to tow the rig to the shop while we are living in it, I. Might have a mobile mechanic that might be able to do it, either way I need to do something before the threat of storms is on us. Thanks
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Saturday, May 6th, 2023 AT 12:08 PM
Tiny
STEVE W.
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Yeah, that can be an issue if you are living in the rig, and it breaks down. Vacuum leaks that you can hear could cause it to run hot but that wouldn't show bubbles in the system. A bad head gasket can cause a misfire, if that one has a doghouse you can pull you could remove that then use some starter spray around the engine to find the leak(s). You could also pull the plugs and compare them, if a gasket is leaking into the engine the plug will be much different than the ones that are not burning coolant. If you find that it is a gasket, and the rest of the coach is in good shape you might consider putting a crate engine into it. A bit more money but you would get a new engine with a warranty. Instead of just a patch on the current one. That would be your choice though.
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Saturday, May 6th, 2023 AT 5:58 PM
Tiny
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The weird thing is I never see the gauge showing overheating, maybe the gauge is stuck or something. Yes I'm about to take the dog house of and see if I can get the plugs off so far I haven't been able to get a plug wire off through the wheel weld, I would expect to find them oily, coolant shouldn't be too hard to distinguish, we aren't planning on doing much traveling in it so a patch up is our most economical option. Are you saying spraying starter fluid with ether around the engine to detect leaks? Any thoughts on the OBD scan?
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Saturday, May 6th, 2023 AT 6:14 PM
Tiny
STEVE W.
  • MECHANIC
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Yes, with the engine cold, start it up and spray at lines and intake gasket areas and listen for the engine tone to change, then look in that area for a vacuum leak.

https://www.2carpros.com/articles/how-to-use-an-engine-vacuum-gauge
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Saturday, May 6th, 2023 AT 6:43 PM
Tiny
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Surprising update, I had the dog house open, I was looking to take off the plug wire which seems a task in itself, when I dropped a wrench on the ground, below the driver's side lay a short hose as you can see in the first picture, I almost blew it off, but something told me to pick it up and see if it goes to the engine, sure enough, it was missing I put it on as you can see in the second picture I put it back thinking to myself it can't be that simple, in the hopes that it would change something, said a short prayer and fired it up and sure enough no more high idle to stall, smooth as butter it's obviously a vacuum hose, that had been disconnected and I probably just knocked it on the floor today, I don't know why it got disconnected and  I'm still going to have to figure out what the smoke from the manifold is about but at least I don't have that vacuum issue to figure out.
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Saturday, May 6th, 2023 AT 7:28 PM
Tiny
STEVE W.
  • MECHANIC
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Yeah. That hose looks cooked, that's why it fell off, the easy solution is to take the rubber section off the line you have and get a chunk of vacuum line of the same size. Now just cut a piece off the same length as the piece on it and replace both ends. I would look at the other lines as well, the hoses get heated and start to break down and leak. I would probably suggest replacing all the lines simply due to age based on the way that line looks, keep other problems away for now. Then run it and see if it stays cool.
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Saturday, May 6th, 2023 AT 8:22 PM
Tiny
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Will do, thanks
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Saturday, May 6th, 2023 AT 10:14 PM
Tiny
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Got some good news and bad news, bad news first I broke a bolt, good news one of the bolts to the manifold was loose, as you can see in the picture it's the one on the left, unfortunately, the bolt that broke may be related to the manifold or it's just to hold the plug wire in place as there is a bolt on each fitting that goes around the wire. I'm already thinking about extraction, not the easiest spot to get to with a drill, or try to JB weld the head to the bolt providing there doesn't need to be much torque, but if it's related to the manifold, I would think the torque needs to be high. Any idea if it's for holding the manifold, my guess is the bolt is so rusted in it's not going anywhere.
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Sunday, May 7th, 2023 AT 10:36 AM
Tiny
STEVE W.
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Looks like an exhaust manifold bolt. Not a major issue but it could be a bear to extract without a lot of work.
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Sunday, May 7th, 2023 AT 3:15 PM
Tiny
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Yes, that's what I kind of figured, the bolt seems to also hold in the fitting plug wire is held in place by, for now I have the plug wire in it without it. I started it up, and there is still smoke coming from the manifold, not from where the bolt was loose but more like from in under where the spark plugs go. Upon looking closer the oil cap appears to have muddy like residue and the oil seems to look tanned, I know those are symptoms of a blown head gasket, I did the bubbles test again and nothing came out, it be low on coolant, or I might have not done the previous test with the engine cold. I will add coolant and try again tomorrow.
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Sunday, May 7th, 2023 AT 7:34 PM
Tiny
STEVE W.
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Good luck. You can usually get the pressure testers as loaner tools (more like rentals as they make you buy the tool then give the money back when you return it) but that might show it better.
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Monday, May 8th, 2023 AT 7:25 AM
Tiny
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Yes, that's what I understand $250 deposit at AutoZone. Do I need to do a compression test as well? I know they loan those kits out too.
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Monday, May 8th, 2023 AT 10:08 AM
Tiny
STEVE W.
  • MECHANIC
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Shouldn't need it, you just need the pressure test kit.

https://www.2carpros.com/articles/radiator-pressure-test

First top up the coolant with the engine cold. Then follow the instructions on the kit to connect it. Now start the engine and watch the gauge. Normally the pressure in the cooling system is from the hot coolant expanding and pushing past the rad. cap at 12-15 psi. That generally takes a while because the engine has to heat up. So, if you ran the engine for say 15 minutes, I would expect the pressure gauge to get to 10-12 psi. What you are looking for is a much faster rise in pressure from combustion gases getting into the cooling system. So, you start the engine and within 2 minutes you are seeing 10 psi, that is a bad head gasket. Or if you want to check for a leak the other way, pump up the tester to whatever the cap says and wait. If you come back in 1/3 hour and it's at the same pressure you don't have any leaks from the cooling system or into the engine. However, you could still have a bad head gasket because combustion chamber pressures are much higher, and it could act as a one-way valve. Now if you run it a few minutes and you don't see any pressure then it's possible that you don't have a gasket problem, but with the oil color and residue I wouldn't count on that.
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Monday, May 8th, 2023 AT 11:24 AM
Tiny
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I understand and will post the results. Thanks
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Tuesday, May 9th, 2023 AT 5:10 PM
Tiny
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Well, I still haven't tested it since I haven't had to drive it, but now I have a starting issue and I think it's wiring related. I will make a new post.
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Thursday, June 1st, 2023 AT 8:46 PM
Tiny
STEVE W.
  • MECHANIC
  • 13,015 POSTS
Not a problem. Life takes precedence over other things. When you get back to it just post any updates.
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Friday, June 2nd, 2023 AT 1:08 AM

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