Hey guys, The search funtion doesn't seem to be working this morning. I have an 88 351 f.i. Was running fine one day, the next no start. I checked fire, O.K... Fuel pump working. I changed fuel filter 3 months ago. I disconected the fuel line from pump/filter and it pumps fine. What controlls injectors. I think they are not spraying? Thanks.

 

To answer your question: The computer controls the injectors, but there are lots of things involved. However; you need to check for fuel pressure at the schrader valve on the fuel rail that feeds the injectors (up on the intake manifold). Also, you have a fuel pressure regulator that mounts to that fuel rail - pull the vacuum line from it and check for any wetness. If that regulator goes bad it is often because the diaphram sprung a leak and the engine vacuum will suck gas in to that vacuum line. Also (and I'm guessing here), you may have a two fuel pump setup. You may have an in-tank low pressure pump and a booster pump mounted on the frame rail close to the engine bay that will boost pressure to about 40 psi. Also, if you have duel fuel tanks, things get even more complicated. Make a few checks and get back to us.

 

Thanks I will check those out. Also I noticed that when you crank the engine the pump by the filter stops pumping(or at least I cant feel it pumping) but let off the key and it starts again. Should that pump stay running all the time? What I mean is if you turn the key forward but don't crank it, will the pump continue to run or should it shut off when the pressure builds up? Thanks.

 

The fuel pump will initially run for only a few seconds, then shut off. It will not run again until the engine starts (I believe the computer uses the tach signal). Your system has to hold pressure for the engine to start.

 

Under the hood, near the L hood hinge, there are 2 relays. One has a brown connector; the other has a bright lime green connector, which is the fuel pump power relay with 4 wires. One of the wires will be either T/LG or LB/Or. Connect a small 12V test light to that wire, and to the Y wire (battery +). Turn the key to RUN (not START) for about 15 seconds and observe the light. Post the result.

Yes, '84-89 EFI have an external pump & the crappy fuel reservoir on the frame rail. The EEC uses the PIP signal, which isn't the same as TACH.

 

O.K. Put a light on the relay. When the light was hooked up to the T/LG wire and the + the fuel pump ran and then shut off(like it should) with no light hooked up, it stayed running. With key on start, 15 seconds, no light ever came on? I tried to crank it and after about 4 seconds the light came on very dim.????? any ideas?

 

So Comfort, I pulled the vacuum hose and found no wetness. Sorry but I have no way to pull a vacuum test for the pump. What does the schrader valve look like? And how do I check to see if it is ok? Thanks

 

Any thoughts? Anyone?

 

There isn't any "vacuum test for the pump." The vacuum line going to the fuel pressure regulator just provides a 4 to 5 psi spike in fuel pressure on throttle tip in (the equivalent of the accellerator pump on carburated cars). The schrader valve looks like the ones on your tires or the A/C compressor. It also resides under a similar valve cap, but on the fuel rail. After your fuel pump has run for a few seconds, you should have pressure if you push on the center of the valve. Hold a rag over the valve, as you will get a spray of gasolene if all is well (should be at about 39 psi).
The PIP signal Steve83 refers to is the output of the reluctor in the distributor, and will be there if you have spark. Your first objective should be to determine if you have fuel pressure at the schrader valve.

BTW, do you have dual gas tanks? This may end up being a problem in the fuel reservour area Steve83 referenced, but we need to determine if you have sufficient fuel pressure (and if you do, if the injectors are firing).