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intake gaskets? coolant leak, smoke test, codes
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Hello, I am trying to diagnose my truck before taking it apart or taking it somewhere. I believe it is lower manifold gaskets but would appreciate any input. I will do my best to explain what I've tried, and where I'm at.
Thank you in advance! I got this truck in trade a few weeks ago, it's a 1999 mazda b4000 aka ford ranger 4.0 V6 OHV, ~165k. CEL codes at the time were p0174+0171, running lean both banks, and p1506 IAC duty cycle high. (also p0500 for vehicle speed sensor but assuming unrelated) Looks clean under the hood and there appear to be new plugs, wires, and vac lines. fuel filter has also been changed. It was supposedly a daily driver and ran well at first, but RPMs were always higher than normal, which worried me. Then idle became rough, wanting to stall. heard whistling around the air filter box, changed loose air filter, disconnected battery and cleaned MAF and IAC with maf cleaner. after relearning idle, truck seemed to run perfectly at normal rpms for one day, then next day rough idle returned with surge/plunge/stall misfire that went away when engine warmed up. It was driveable locally for a few days. Then (of course) coolant started leaking at the water pump weep hole so I took it to a shop, not wanting to tackle that in the single digit temps. asked them about the idle and they said it was acting like vacuum leak from intake manifold, but further diagnosis would be necessary. When I drove it home was running rough, always wanting to stall at low rpms. Checked codes, and new ones were: P1131+1151 'lack of switches' indicates lean, P0113 Intake air temp sensor high bank 1, and p0136 02 sensor circuit bank 1 sensor 2. (I believe all of these can point toward a massive vacuum leak? or bad MAF, but you'll see why I ruled that out.) When I started it the next morning, there was a new large steady leak of coolant below the rear of the engine, dripping from the bellhousing. Can't see exactly where it's coming from above that, but I am guessing somewhere on the passenger rear of the engine/compartment. There is nothing visually obvious that I can see from above. It's a significant amount of coolant dripping, only when truck is running. I did a home-made smoke test (worked pretty well!) and smoke was coming up from beneath the coil pack. so a vacuum leak is definitely confirmed... I don't know if any vac lines run under there, if anyone is able to deduce more from the video, I'd appreciate it. At this point I am pretty convinced that it is upper and/or lower intake manifold gaskets, and the leaky airbox hid it from me for a while, then when the coolant pressure was corrected, it finally blew a gasket... but I want to make sure I'm not overlooking another possibility. head gaskets? cracked heads? something like that? or a combination of unlucky unrelated things, like a bad MAF/IAC and a coincidentally bad freeze plug...AND a vacuum leak? seems like a stretch. Whether to attempt them myself is another question... it seems like a fair amount could go wrong with how much has to be taken apart, and a big job if that's not the problem. https://cimg1.ibsrv.net/gimg/www.ran...4c378f2d84.jpg |
Originally Posted by rangerb4000
(Post 2235805)
Hello, I am trying to diagnose my truck before taking it apart or taking it somewhere. I believe it is lower manifold gaskets but would appreciate any input. I will do my best to explain what I've tried, and where I'm at.
Thank you in advance! I got this truck in trade a few weeks ago, it's a 1999 mazda b4000 aka ford ranger 4.0 V6 OHV, ~165k. CEL codes at the time were p0174+0171, running lean both banks, and p1506 IAC duty cycle high. (also p0500 for vehicle speed sensor but assuming unrelated) Looks clean under the hood and there appear to be new plugs, wires, and vac lines. fuel filter has also been changed. It was supposedly a daily driver and ran well at first, but RPMs were always higher than normal, which worried me. Then idle became rough, wanting to stall. heard whistling around the air filter box, changed loose air filter, disconnected battery and cleaned MAF and IAC with maf cleaner. after relearning idle, truck seemed to run perfectly at normal rpms for one day, then next day rough idle returned with surge/plunge/stall misfire that went away when engine warmed up. It was driveable locally for a few days. Then (of course) coolant started leaking at the water pump weep hole so I took it to a shop, not wanting to tackle that in the single digit temps. asked them about the idle and they said it was acting like vacuum leak from intake manifold, but further diagnosis would be necessary. When I drove it home was running rough, always wanting to stall at low rpms. Checked codes, and new ones were: P1131+1151 'lack of switches' indicates lean, P0113 Intake air temp sensor high bank 1, and p0136 02 sensor circuit bank 1 sensor 2. (I believe all of these can point toward a massive vacuum leak? or bad MAF, but you'll see why I ruled that out.) When I started it the next morning, there was a new large steady leak of coolant below the rear of the engine, dripping from the bellhousing. Can't see exactly where it's coming from above that, but I am guessing somewhere on the passenger rear of the engine/compartment. There is nothing visually obvious that I can see from above. It's a significant amount of coolant dripping, only when truck is running. I did a home-made smoke test (worked pretty well!) and smoke was coming up from beneath the coil pack. so a vacuum leak is definitely confirmed... I don't know if any vac lines run under there, if anyone is able to deduce more from the video, I'd appreciate it. At this point I am pretty convinced that it is upper and/or lower intake manifold gaskets, and the leaky airbox hid it from me for a while, then when the coolant pressure was corrected, it finally blew a gasket... but I want to make sure I'm not overlooking another possibility. head gaskets? cracked heads? something like that? or a combination of unlucky unrelated things, like a bad MAF/IAC and a coincidentally bad freeze plug...AND a vacuum leak? seems like a stretch. Whether to attempt them myself is another question... it seems like a fair amount could go wrong with how much has to be taken apart, and a big job if that's not the problem. https://cimg1.ibsrv.net/gimg/www.ran...4c378f2d84.jpg Check your radiator for the smell of hydrocarbons. This is a tell-tell sign of an head gasket issue. You can also run a compression leak down test. They also have lower intake gasket issues. My 99 ohv lower has started to leak as well. That upper plenum gasket, has been known to deform and can cause a vacuum leak. Good luck |
hey thanks for the feedback - that tracks with what I am finding. will hopefully do a compression test this week.
Just a quick update: No coolant leaks at the heater hoses or components anywhere along the firewall or top of engine compartment. definitely seems to be coming from the back of the engine. leak is a slow but constant drip when truck is off (haven't restarted it). put a mirror down there but couldn't accurately judge where it's coming from. I also drained the oil, it looked very sludgy and bubbly. not really watery though. (sign of neglect or overheating) https://cimg4.ibsrv.net/gimg/www.ran...193cd408c3.png https://cimg9.ibsrv.net/gimg/www.ran...40e977c06a.png https://cimg9.ibsrv.net/gimg/www.ran...3a5b52ffe1.jpg |
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