96 T100 Horse Power Loss
02-23-2018, 12:46 PM
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96 T100 Horse Power Loss
I have a 96 T100 maunual transmission with 318k. Over the past two months, I’ve been experiencing a massive power loss when going uphills and when trying to accelerate quickly, like getting on the freeway. I switched the plugs and wires, which were about 50k old. The old ones were toast, but seemed to just have normal wear. I also have a very minor head gasket leak around cylinder 6. Pretty typical for this year, from what I’ve read. I’m going to a chain auto parts store to pull codes next week. She has a slight hesitation off the line and flooring it doesn’t seem to do much, even on flat ground. I know she’s old and pretty beat up, but in December, she was still charging hard. I’ve read about clear different valves and the MAF. Any thoughts? Also, my muffler has a massive hole and is loud as hell. It sometimes sounds almost like glass packs when I’m riding gears going down hill. New muffler and pipe are en route. Could my cat be wrecked? Everything is original, minus timing chain (although it’s been 90k since the last change) and suspension. I always enjoy getting info and tips here so hopefully some of you have some insight. I’d like to try and keep her charging until at least 400k. Thanks!
03-28-2018, 08:27 AM
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Got the computer codes back. It threw MAF sensor and IAT sensor circuit. I replaced the MAF and coil packs. Packs were old anyway and possibly originals. Engine runs more smoothly but now won’t rev past 3200 rpm and it’s very slow off the line, even on flat ground. I couldn’t find the IAT sensor. Haynes manual shows it being attached to the air box but there is no hole or wires anywhere. Did the PO possibly rewire the IAT? Is there a different location it might be? I’m pulling my cat to see if it’s clogged and replacing the fuel filter today. Any help would be appreciated.
03-28-2018, 11:54 PM
#3
Don't pull the cat, you just need to do a pressure test before and after to see if there's a difference, small hole for the test, and a quick buzz up to patch it. I doubt it's the cause though, I've never seen one plugged on a Toyota even the one I have with over 500k miles isn't plugged. Cats normally don't go bad, unless there's another cause like bad O2 (dumping way too much gas) and it takes a while at that, pretty uncommon to find.
My money is on the already mentioned head gasket, do a compression test on each cylinder, I bet 6 will be low and maybe other's bad too. Another check is to pull the spark plugs, they all should be the same and kind of a light brown type of color. If any are super clean (while miles on them), there probably is a head gasket leak where coolant is getting in the cylinder. Over time it will wash out your cylinder and require a bore increase to properly fix the engine. Either case fix the head gasket asap since it will fail sooner rather than later.
For the mention of the valves, I've heard the 3.0L (what the 3.4L is based on) has an issue with burning exhaust valves. I don't think the 3.4L has that problem often, but could be possible. While you do your headgasket, I'd defo check out the head/valves too. Wouldn't hurt to have the valves reground and such.
You have a service manual, did the old coil packs test bad or something? Never blindly replace parts, you're just throwing money away for no reason. I'm personally not a big fan of "off brand" service manuals, but you already have it so hopefully it's accurate. I have Toyota EWD (Engine wire diagrams) that I could probably pull some specs from if you wanted to double check.
Air flow meter has a built in IAT sensor, testing the part should show it's out of spec, and you can test the new part to validate it doesn't have the same issue.
These trucks use really reliable parts, sometimes it's as simple as a broken wire or a poor connection. Japanese electronics rarely fail from what I've seen except in a couple of cases (the dash clock comes to mind with it's odd internal spring style connector for board to plug connection). Also on the replacement parts, I personally always run OE/OEM parts except in rare cases where I don't care much. Denso/NGK for plugs/wires, NSK for bearings etc.
My money is on the already mentioned head gasket, do a compression test on each cylinder, I bet 6 will be low and maybe other's bad too. Another check is to pull the spark plugs, they all should be the same and kind of a light brown type of color. If any are super clean (while miles on them), there probably is a head gasket leak where coolant is getting in the cylinder. Over time it will wash out your cylinder and require a bore increase to properly fix the engine. Either case fix the head gasket asap since it will fail sooner rather than later.
For the mention of the valves, I've heard the 3.0L (what the 3.4L is based on) has an issue with burning exhaust valves. I don't think the 3.4L has that problem often, but could be possible. While you do your headgasket, I'd defo check out the head/valves too. Wouldn't hurt to have the valves reground and such.
You have a service manual, did the old coil packs test bad or something? Never blindly replace parts, you're just throwing money away for no reason. I'm personally not a big fan of "off brand" service manuals, but you already have it so hopefully it's accurate. I have Toyota EWD (Engine wire diagrams) that I could probably pull some specs from if you wanted to double check.
Air flow meter has a built in IAT sensor, testing the part should show it's out of spec, and you can test the new part to validate it doesn't have the same issue.
These trucks use really reliable parts, sometimes it's as simple as a broken wire or a poor connection. Japanese electronics rarely fail from what I've seen except in a couple of cases (the dash clock comes to mind with it's odd internal spring style connector for board to plug connection). Also on the replacement parts, I personally always run OE/OEM parts except in rare cases where I don't care much. Denso/NGK for plugs/wires, NSK for bearings etc.
03-29-2018, 07:26 AM
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Fix your known problems first. It sound like you are sure you have a slight head gasket leak, it NEEDS to be fixed before it gets worse and if it fixes your other issues, BONUS. If not you can eliminate a lot of possibilities while you are there.
11-23-2018, 06:55 PM
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Hey
Got the computer codes back. It threw MAF sensor and IAT sensor circuit. I replaced the MAF and coil packs. Packs were old anyway and possibly originals. Engine runs more smoothly but now won’t rev past 3200 rpm and it’s very slow off the line, even on flat ground. I couldn’t find the IAT sensor. Haynes manual shows it being attached to the air box but there is no hole or wires anywhere. Did the PO possibly rewire the IAT? Is there a different location it might be? I’m pulling my cat to see if it’s clogged and replacing the fuel filter today. Any help would be appreciated.
11-23-2018, 11:39 PM
#6
Makes sense to me, I never ran into it personally, but my dad has had to replaced some plugged ones since he's a mechanic. I think they generally fail from the O2 sensor being bad and dumping too much fuel. Seems so many people don't care about the O2 sensors when it's a pretty critical sensor for a happy engine.
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