My son’s 1990 Dakota 3.9L with throttle body FI (165K) has run great for the last several years. Last week it began running very rough. It starts fine, but sputters badly at idle, sometimes quitting. Depressing the gas pedal will increase rpms but it continues to sputter and then for a second or two “catches” and runs smoothly (rpm jumps) and then goes back to sputtering. I can be driven–barely. Seems right on the verge of dying and catches with a lurch forward. We changed the fuel filter and I could hear the whirring of the fuel pump when key is turned to the “on” position while my ear is on the filler tube. Haven’t done a fuel pressure test yet–need to get the gauge kit. Before I get any farther (i.e. purchase fuel press. gauge) does it sound like I’m on the right track? If my son wasn’t a starving college student and I a starving parent of said college student, we’d just take it to a repair shop. Might have to eventually, but does anyone have any advice on what I should be looking at? Many thanks!
Sven
The fuel pressure might be the first thing to look at, especially if the old filter had been on there a long time and was even partially clogged.
Lacking a fuel pressure gauge at this point, you might remove the service port cap where the fuel pressure is checked, and while someone cranks it over or you jump the fuel pump relay, wrap a rag around the port and depress the Schrader valve with a tiny screwdriver tip, matchstick, etc. and note if gas sprays out under significant pressure.
That’s not a real scientific method but it can work.
If you have the old fuel filter still around you might try blowing through it and noting if it’s clear or not. You should be able to blow freely through the filter now that it’s dried out. If not, it’s partially clogged and a filter like this will take out a fuel pump.
One wants to do the inexpensive things, first. If you have an Auto Zone, or such, just around the corner, maybe you could get the truck there for a (free) reading of the trouble codes, if the check engine light is on. While there, get the MAF spray cleaner, another cleaner for the intake track (including the iac valve [idle air control]) and throttle plate. Also, a can of spray Starter Fluid. Stop by the public library and get the Haynes repair manual, or go on line for Alldata automotive information (ask a librarian for assistance). Check under MISFIRE. Use the spray cleaners. Use the spray Starter Fluid when the engine begins to stumble. If it stumbles less, the problem is fuel. The fuel could be bad. The fuel pressure may be low. The fuel injectors may be spraying erratically. Some Techron Fuel Injector Cleaner could clean fouled fuel injectors. For bad gas, one replaces the bad gas and fuel filter.