fuel injection issue

[RBrandon]

Ok. this question pertains to a 4.9 6-cyl on a ford f150, but you guys are smart and I never got a reply from the ford forum so here goes... My father-in-law has a ford truck with the 4.9 straight six, 1990. It has ample pressure measured on the fuel rail. It will crank on ether. Has spark at the plugs. It will not run however. The TPS has been swapped out. The only thing I can think of is that none of the fuel injectors are firing. I only have a digital multimeter and it wont read quick pulses like a needle movement would. Either way, with fuel at the rail and spark at the plugs, the only option is that the computer isn't telling the injectors to fire. Assuming that the computer is getting power and working, then something isn't telling the computer to actuate the injectors. I am told that this would be a crankshaft position sensor but Haynes doesn't mention one, and we can't find it. Anyone know enough about fuel injection to extrapolate and make an educated guess for me? My father-in-law would appreciate it.

[bringselpup]

Is there something that is the equiv to the cam position sensor on it?

I'm thinking if it's fuel injected it has to have some sensor to tell the system when to fire the injectors.

1990 truck also, I wonder is the computer ok.

[fredjacksonsan]

That year had a cap and rotor setup, right? If it's at all similar to the 5.0, there is a sensor in the distributor called the Hall Effect Sensor. If that goes bad then it won't know when to fire. You have to remove the distributor to replace it though, so I'd eliminate other stuff prior to tackling that job.

[RBrandon]

Thanks for the replies. I will do some research on the hall effect sensor. I am at a loss here since it's not my vehicle and what I learn, I tend to learn while fixing it when it comes to vehicles. I also hadn't thought about the possibility of a sensor being on the cam. I just knew that some had sensors that looked at the flywheel and was leaning that way. I will probably fight my way to the computer at some point and verify power at the harness, just to rule it out. Quick question: the hall effect sensor isn't part of the TFI module is it? He changed that out if that's the case. I will be leaving Wednesday for an extended vacation so I won't be online much for the next week and a half. Thanks for your help thus far.

[fredjacksonsan]

Welcome on the help, we've all been there. I don't know what the TFI sensor is, but I do know the Hall Effect is separate from other stuff. Ask your friend if the truck would sometimes quit, then restart after waiting for awhile. Classic Hall Effect pattern. Other than that I'm not sure what could be wrong.

[RBrandon]

I did some quick research on hall effect sensors last night. Pretty cool stuff, unless it doesn't work. Apparently it generates a square wave (dc) used as a trigger for the computer. One of it's uses: telling computer when to fire fuel injectors. Who would have thunk it? Thanks again for the lead. I will suggest to my father-in-law that he swap it with one in his other f-150's to test and see. I will let you know how it went in about a week and a half. I'm headed to Oklahoma tomorrow bright and early, and then on to Texas for some needed vacation.

[fredjacksonsan]

Enjoy your trip...be interested to see what the end result is.

[RBrandon]

Well, it only took me months to reply, (life's been busy) but it ended up being his computer. He replaced it and it runs fine. Thanks for the interest, sorry for the delayed response.