View Full Version : newbie for 1995 GM 5.7l tb1 troubleshooting

02-24-2012, 07:52 AM

thanks for letting me join, looks like a great site for fuel injection. I am trying to diagnose a problem with fuel pump relay not coming on for 3 sec start, coil is good on relay, and pump will run when jumpered, looks like no power from ECM , possible ignition switch or oil pressure switch?

02-24-2012, 09:03 AM
Sounds like it's not getting power from ECM when key on? Don't know what PCM you have but here's one for 1995 16197427, F6 sows power to energize relay. All the wiring diagrams can be found here:


02-24-2012, 09:11 AM
Not saying this is your problem, but I helped a guy troubleshoot this a few weeks ago. he was having the same issue and it turned out to be the ECU. swapped ecu's and it worked like a charm. If you jump the relay and the pump turns on does the truck run? on your truck there should be 2 ecm fuses under the dash. if the bottom one is blown the FP won't come on either.

02-24-2012, 09:14 AM
If the relay dosent energize for the prime or while cranking it could be the ECM not sending a siginal, also could be the fuel pump fuse located near the relay, these two come into play for the prime cycle and during cranking .

If the pump will not run with the engine running on it's own without hot wiring it , check the OPSU (Oil pressure sending unit), it is what powers the fuel pump after the engine starts and it "sees" oil pressure.

Let us know model and engine and possibly ECM , might be able to offer more help.


02-26-2012, 01:58 PM
hi fellas,
thanks for replys, have the ecu 16197427, have swapped, no change, all fuse good, no power from ecu?, no check engine light, no response when I jumper diag ,will use the above guide to further trouble shoot, thanks for all the schematics, great help, looks like power not coming from ecu fuse box, wiring is on G30 5.7 and this area is prown to moisture by the looks of it, will do more checking fist of week, too bad about Daytona, sic day tommorow? I have a switch with green and black wire from key switch on column, this green wire appears to be same as one feeding fuel pump reay, can't find reference on schematic. it also has a cable connected that goes up ito top of column, not sure what its purpose is; I see F6 for relay feed on PCM it looks like a dashed line, is this a fusible link?

02-27-2012, 04:35 AM
G Van??? Oboy. OP switch does not power relay. OP switch OR relay can power fuel pump. Make sure you check both sides of the bulkhead conenctor where all the circuits pass through the firewall. It's located in front of the fuse box (remove fuse box then you can get to connector). I've had plenty of issues there. Cable up column is BTSI prevents shifting out of park without pressing brake. Can usually disable system by disconnecting electrical connector.

03-08-2012, 01:09 PM
update, checked for power at ecu, battery power,orange e16 drop to 1.5 volts when plugged in , ignition power there 12.5 volts, when ecu is unplugged I see 12.5 on e16 connector, but drops when plugged in, have not tryed applying another 12 volt source, any new ideas out here, oh and I took the connector for fuse box firewall side apart and it was wet,clean and dryed check connections, there is good continuity to grounds and these power sources, could ecu pull down voltage, but not blow fuse, help.

03-08-2012, 02:18 PM
are you plugging and unplugging the plugs on the PCM? I thought all measurements were supposed to be taken with the PCM plugged in?

03-08-2012, 02:42 PM
all measurements are supposed to be done with a breakout box installed, which means all of the circuits are actually plugged in, but you can non-invasely monitor circuits without removing the insulation from circuits.

03-08-2012, 07:21 PM
has anyone seen low power feed from battery to ecu, when plugged in ?, this is pin E16, checking power by back probing connector and I only see abou1.5 volts, orange wire, E15 has pink wire from ign feed and it is good. Power from both fuse circuits for ECU, at box is good, have had connector apart and verified wiring is ok between fuse box and ECU... maybe I just need to try a new ECU, how much?

03-08-2012, 07:24 PM
check the voltage at two places(with the ignition on): at the ECM connection, then where the ECM sources it's voltage.

that kind of voltage drop would imply that a wire that feeds the ECM has high resistance, causing the voltage drop.

a bad ground would likely do the same thing.

when you find a spot that has 12V, the wiring should be fine there, but further into the circuit the problem must be.

03-13-2012, 02:43 PM
added new wire to feed E16 and, check engine light on, fuel pump started , cranked all is well , truck started and ran. Knowing what i know now, AND having schematics I will start at PCM I guess something this old is bound to have wiring issues from corrosion. Thanks for the help and maybe over time I will be better able to troubleshoot these older systems. Your site has been helpful for an old ford guy still friggin with carbs, thanks again.:thumbsup: