My fuel pump does not prime on my 90 GTA (TPI). The fuel pump fuse (shown in picture in thread link below) tests OK, as does the FP relay -- getting the audible click and get good continuity when energized. Engine cranks strong (of course engine does not fire up), but no usual FP prime "hum" sound prior to crank.

Common sense check: This should not be a battery problem, right? I mean if the starter motor cranks well then there shouldn't be a power supply problem to a dinky little fuel pump. I'm attempting to prime the FP without cranking so any power loss from sharing loads is eliminated. Have to ask though as a bad battery has bit me before.

My guess is the FP went **** up or a mouse chewed on the power wire leading to the FP.

Also depressed the valve nipple on the TPI fuel rail and noticed no pressurized hissing and no fuel drip (figured that would be the case after sitting for a few weeks but why not).

If the gas tank went dry, would the fuel pump still make the typical hum sound? I should think so. Thought I would ask as there is a possibility the tank is dry.

I posted previously to this thread (https://www.thirdgen.org/forums/elec...ml#post6482933) however it is in the wrong forum section, so I'm re-posting here.

 

Have you checked power at the relay to pump or 3 plug connector at tank ?

 

I have confirmed that power from battery to relay is good. Was planning to check power at the fuel pump next, unless you can think of anything else that I should check before doing that.

 

 

Thank you for the diagram. I see in the diagram "FUEL PUMP TEST CONNECTOR" and believe this is what RBob is referring to in his post here:

Is the test connector shown in the attached picture the same?

 

Where is the Fuel Pump Oil Pressure Switch located? A picture would be much appreciated if you have one.

 

It’s one of two places, probably not your issue.
located drivers side next to distributor or could be on side of block above the oil filter.

 

Thanks, I agree, just thought this would be good to know.

 

Put 12V on the fuel pump test connector and do not get fuel pump prime (hum sound). Instead getting a brief and faint "budge"/"thump" sound coming from rear of car (guessing an electronic switch). Also supplied 12V on the FP relay switch-on pin wire ("E"/grey) and get the same response. Measured 12.x V at the fuel pump relay. Concluded that the fuel pump relay is good as well as the wiring up to the fuel pump relay and that a signal is making it to the rear of the car.

My money is on a bad fuel pump.

 

Are you 100% sure that it's not priming? I thought mine wasn't because I've never heard it, and my car always takes forever to start when cold, but there's no way to properly test it that I know of without using 2 people (one to turn the key on, one already waiting underneath the back of the car to hear the humming noise before it stops after 1 second or so). I never could hear mine over the key buzzer, or get to the back of the car before it stops priming after turning the ignition on.

One way to know for sure if it's a fuel issue: spray starting fluid (or anything flammable) into the throttle body, and see if it will start up and run for a second.

 

My FPs have all been AC DELCO and noisy. They have lasted quite a while (~10 years) and being able to hear the unmistakable prime is a plus for troubleshooting IMO. But for sure it was not priming. I swapped out fuel pumps and it fires up again.

One word of warning, do not use a Master Pro 95 PSI fuel pump if you are all stock (wiring and sending unit). O'Reilly's will tell you it works with your TPI third gen but they don't know what they are talking about. Your car will not be able to provide enough current to power it and you'll be swapping in the correct EP241 fuel pump, which is 42 PSI. I am very glad that I have a fuel pump access panel, as the thought of dropping the rear suspension, exhaust and tank TWO F'ING TIMES is enough to give one nightmares! Instead it was 30 minutes for each swap (albeit not very fun). I would only recommend this if your tank is clean inside.

Appreciate all the help!

 

Something that I personally like to incorporate into all of My Customer's Third-Gens is...

An OBDII Connection that has been turned into Jump/ Prob Points (that Bypass the Relays) for Electric devices, like:
-Each Fuel Pump.
-Each Radiator Fan.
-Each Fluid Cooler Fan.
-Each Inter-Cooler Fluid Pump.
-Each Vacuum Pump.
-Each Oil Scavenge Pump
-Etc...

The Terminals inside the OBDII Connector can be configured for either a Ground Activation or a 12 Volt Positive Activation.
There are 16 Terminals available... so there many options for which Electric Devices a Customer would like to choose.

I will install the OBDII Connector under the hood if the OEM ALDL Connector is still being used.

If a Gen-III/ IV SBC Engine Swap has been done...
I will replace the ALDL Connector with the OBDII Connector.

 

According to this Chiltons layout diagram for a 1990 5.0L TPI engine, the fuel pump test connector is at the C8 Location. That does seem odd as the test connector I would have thought, should be near the fuel pump relay.
N7 is the oil pressure switch location according to this diagram as well.



Using a fused jumper Pin G on the ALDL (Assembly Line Data Link), can also be used to test the fuel pump which bypasses the fuel pump relay.
Changing the fuel pump out is a big job, so I would recommend checking it out very carefully including at the connector near the tank, before going down that path.



There was a small clip on my tank connector that had to be slid out, before the tank connector could be separated.

 

I always check the fuel pump ground too. It’s either under the rear driver side seat cushion or just forward of the drivers front seat under the carpet near the rocker. Worth checking as it’s a much easier check than dropping the tank and finding out it’s something else.

 

some relays do have a red pigtail to apply 12v to put power to the pump . The relays at the bulk head next to the booster. Not all aldl have G most don’t .

 

Thanks, good information. I guess I am one of the lucky ones then, as my car does have the connector installed.


I don't know if this has been mentioned yet but make sure you check the fuel pump fuse to make sure it is OK. Mine on my 1986 i has a red and orange wire going to it. Yours looks to located next to the Battery according to the Chilton's layout drawing.

 

Sorry guys I think I need to pay a little more attention to the dates on these posts as it looks like I am responding to a 2 year old post.