Marie wrote:243,000 miles, two-wheel drive, regularly and lovingly maintained since new by same owner but all work is done by technicians. I frequently reference my 1989 - 2002 Haynes Repair Manual to keep up with work that is done, sticking to the recommended Isuzu mainteneance schedule since new. In last couple years, it chokes back intermittently when I accelerate, coughing (no backfire) as if it can't breathe. Check engine light comes on intermittently. Technician just replaced fuel filter, air filter, spark plugs, distributer cap & rotor, replaced coil (ignition timing), cleaned EGR valve, flushed power steering fluid, fuel pressure test. Technician not sure what to do next. Any suggestions ?
Hi, Marie, Welcome to the Planet! Your GM 3.1 V6 is a pretty reliable Stone-Age Iron Beast, but there are common issues that crop up, especially with hi-mileage engines. One very common issue is timing chain stretch. Usually the chain stretches which changes the cam timing, eventually it becomes very sloppy and can even break. The timing "damper" that sits in the middle of where the chain runs, has rubber "slipper shoes" bonded to its metal frame. The rubber gets old, hardened, and sometimes breaks. Then the chain rides on the metal, causing havoc.
Your mechanic can check for a sloppy timing chain by rocking the crankshaft pulley back and forth while watching the distributor rotor. If there is a lot of lost motion between when the crankshaft moves and the rotor moves (there should be none), the timing chain is stretched.
But since the engine computer (ECU or ECM) is setting a trouble code, your mechanic should be reading that to find out what code is set. It might point to a solution.
Note that there's a specific way to check timing, there's a wire in the center console called the EST (Electronic Spark Timing) wire. This wire must be unplugged from itself (it's got an inline connector) before trying to read the timing. Long as the mech. has done this, timing should be ok. Factory setting is on the decal on the underside of the hood, probably about 10 degrees BTDC (Before Top Dead Center).
Mech. should also check the (2) fuel injectors in the throttle body for proper spray pattern. If the injectors are partially clogged, that's going to cause a lean condition and a "bogging" problem. There should be a full, fan-shaped spray coming out of each injector. Any dribbles or missing segments of spray indicate problems. I'd recommend rebuilt injectors if they require replacement, Rockauto.com is one good source for those. Or eBay. Any number of companies "rebuild" these by cleaning, reassembling and flow-checking. Good as new!
Another pesky problem I've had (and many others here) in the past, is failure of the Engine Coolant Temperature sensor (ECT or aka ECS). When this happens, the engine will run poorly if at all. This sensor screws into the middle of the intake manifold, just forward of the TBI (Throttle Body Injection) unit. It's easy to replace, with a cooled-down engine you don't even need to drain the radiator.
A very easy way to rough-diagnose this sensor is to unplug it. This of course will set a "check engine" lite and trouble code. If the engine runs better, the sensor is definitely perished. It's not gonna run real sharp but if your symptoms are different, likely it's an issue. The sensor can be checked for proper resistance at a given temperature, with an ohmmeter.
A few other things that come to mind are O2 sensor (cheap to replace); restricted exhaust system (pressure checks can be done); distributor ignition module. The ign module in the distributor runs very hot and if the heat sink compound between the module and the distributor dries out, the module gets hot and can act up or fail. This heat sink stuff is similar to what's used on computer CPU's (like Arctic Silver, etc).
FIY here's a link to Rockauto.com parts for your '92 Rodeo:https://www.rockauto.com/en/catalog/isu ... v6,1176881
BTW, you may get more help if you post in the "Drivetrain Problems" section, there's a ton more traffic there than in this "test" section.
Or, HEY MODS, maybe you can just move this thread, eh? That would be cool!
HTH & let us know how things work out..............ed
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