'88 Ranger runs 2-5 seconds then stalls
I have an '88 Ranger which I recently bought as a yard/plow truck. When the truck will starts it will run at around 2,000 rpm for between 2-5 seconds, then cut out. If you hit the gas while it is running and keep the RPM around 3,000 it will stay running for up to 20 seconds before it quits. Both the sending unit and fuel pump are working and it has 40 psi at the rail, the fuel pump relay seems to be operating properly.
The problem seems to have been around for a while because the previous owners have installed a new distributor cap and wires, new MAP sensor, and bypassed the inertia switch. The previous owners also rigged an aftermarket fuel tank in the bed.
The check engine light is on and I have been unable to scan it. I have tried cleaning the IAC, testing the fuel delivery system, and checking the grounds for the computer. I would like to get this truck running without throwing parts at it, any advice on testing I can do is much appreciated. Has anyone heard of this problem before? Thanks in advance!