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Hey everyone new to the forum here. I just got a ‘97 T100 3.4l auto 4x4 and have been trying to breath life back into her after being parked for 8 years. Lots of little things as you can imagine but I’m stuck on a couple last problems and the local shops have been less than spot on so far. So far have done the following: battery, fuel pump and filter, spark plugs, injector #6, security shutdown relay, coolant temp sensor, downstream O2 sensor, coolant flush, thermostat and some AC work. Everything is stock but for a hollowed catalytic converter(which might be part of my problems). When I first got the truck, the tailpipe was pointed up too high and the exhaust had melted the insulation off of the taillight wires and had begun to melt the actual taillight assembly. Had someone comment that it was really hot just standing back by that part of the truck. Figured a clogged cat was causing the extreme heat so I hollowed it rather than buying a new one. Truck spent many years as a ranch/hunting truck then was parked for 8 or so years.
1. Truck starts and runs great, until it warms up then looses a ton of power at higher rpm. Runs ok around town and at lower rpm but falls on its face when you ask it for anything more. Seems like a temp sensor of some kind that changes timing/fuel mixture based on engine temp. Maybe running good with a cold start mixture and it never changes causing it to run too rich at higher temps? Anything over 2k rpm I get a hollow rattle not and engine rattle or knock just maybe a loose heat shield or something but it sounds terrible. Haven’t been able to drive it much but it seems to be using way too much fuel. Would like to avoid a new cat if the O2 sensors can be tricked like the older style can be but I know I might be better off going back with a new cat to fix O2 codes.
2. Cruise control doesn’t work. Green cruise light comes on but nothing happens. Cruise motor? Engine code that disables cruise? I believe we had to bypass the security cutout relay?? it was in a anti-theft mode when I first got it running I think.
Thanks in advance any tips would be greatly appreciated.
That rattle you hear is likely one of two things. Either there are remnants of material left in the converter or more likely spark knock. Spark knock, or pre detination, is exactly that. The mixture in the combustion chamber is igniting just before it actually should. This of course in minor cases just sounds bad and major cases can crack pistons and bend rods. Spark knock is usually caused by either early ignition timing (non user adjustable on these truck) or its because its running lean.
It sounds like your truck is running lean. Spark knock will get worse as engine temperature rises. A lean mixture burns hotter and just compounds the problem. In your case you say it gets worse as temperature comes up. Does it get worse gradually or does it happen suddenly. Usually a temperature related lean condition is caused by a faulty coolant temp sensor or a faulty O2 sensor. A coolant temp sensor will try to lean it out more as temperature rises. An o2 sensor that is fixed rich will lean it out completely when it hits closed loop mode. Your downstream O2 sensor wont have any change on the way the truck runs and drives. Its there only to monitor converter efficiency. The upstream sensor will be the culprit. To test if its the O2 just unplug it. Leaving it unplugged should leave it in open loop mode and power shouldn't change much assuming its the problem.
Also, running a gutted converter will negatively affect power. Exhaust velocity is just as important as restriction. A gutted cat will make for an expansion chamber close to the engine. This will completely kill the velocity of the exhaust and affect mostly low end power. Either put new cat on it or at least replace it with a section of pipe assuming you don't have to pass emissions. The rear O2 sensor can be fooled to not set codes. I'm not gunna tell you how to do it since its illegal. If you really want to do it though google it. The information is out there.
Last edited by Kolton5543; 09-19-2018 at 08:47 AM.
Oh and welcome to the forums. Its nice to see another T100 owner. they're starting to become far and few between. Also you posted this in the completely wrong section but no biggy. Just watch out on future post. Some people get a little anal about it. It raises you chances of getting useful help too.
Thanks for the info. I should have known but I guess I’m out of practice on gassers I have only owned and turned wrenches on diesels for the last 7 years or so.
Sounds like the upstream O2 is to blame. It seems to happen quickly as soon as the temp begins to rise. I’ll test it when I get home today and report back. I guess I assumed that the shop had already checked that. Any thoughts on the cruise control?
09-18-2018, 12:57 PM
