No Start/Fuel Pump Diagnosis

[Mic1980]

Hey guys whats up. I just replaced a fuel pump on my brothers 96 Blazer 4.3 SCFI. I'm not sure what brand the fuel pump is yet I might be able to find out but I know its not an AC Delco. The fuel pump comes with it's own connector and according the the instructions I followed them to the letter. 4 wires 1 prp, 1 grey and 2 blk and one of the black wires have a white stripe.

Ok so I installed the fuel pump I have one side held up by the fuel petcock and the other side held up by two 4x4 blocks of wood it's in a bit of a decline it's not even or leveled I should say, however the pump is wired. So I figured I would try to start the blazer and make sure it would work before I put the tank up completely. I used my car to jump the battery so it wouldn't drain from cranking plus I'd say the battery had a little bit more than half of its juice.

Summary: I turned the key on for 2 minutes so the pump can pressurize the fuel lines then I went at it and it just wouldn't start. I noticed the fuel gauge wasn't working ever since I installed the fuel pump so I'm assuming that the wiring is wrong what kills me though is I did exactly what the instructions told me. I'm also going to check the crimp connections. Basically I'm looking for some ideas something I might not have thought of yet because I want to get this car done ASAP.

Note: Car has been checked for spark.
Fuel shraeder valve seems not be pressurized.
and the car starts up with starter fluid.

Thank You

[veedubmechanic]

Did you use the heat shrink connectors that come with the harness pigtail?
Does the pump buzZ when the key is turned on?
Check what brand the pump is. Some of those Chinese pumps are total garbage right out of the box. Sometimes I have had to get 3 pumps before getting one that worked.

[Mic1980]

There were no heat shrink connectors just the regular darker red/blue colored nylon butt connectors. The instructions do say to use heat shrink tubing but they did not come with the package which it clearly shows in the picture upon purchasing.

Pump definitely buzzes when key is turned on and all I can tell about the pump is that it is sold on ebay from AM-Autoparts the seller. Thanks for the reply


http://www.ebay.com/itm/96-Blazer-Br...5c5bcf&vxp=mtr

[aleekat]

Even though you got detailed instructions. I have seen some after market pumps where the + and - was reversed from the original pump.

[Mic1980]

Really? that's bad...

I don't believe that is the case for my situation because I can hear the fuel pump prime when I turn the key on. Also I want to correct a previous statement. The fuel line did have fuel coming out of it when I checked today, and I think yesterday when I checked for pressure I didn't have the key to the on position.

I just double checked the wiring and terminal A of the connector is purple, B is grey, C is solid black, and D is Black with white stripe. I jumped the fuel pump to check for voltage just to see if there was a decent amount and the pump wire had 11.7 volts and the purple wire had 7.6 but I did it twice and I could tell the battery is dying because it dropped 3-4 volts on each wire the second time I'm also going to charge the battery because I read that these blazers need to crank pretty fast to start up.

[old_master]

When you initially turn the ignition to the RUN position, the grey wire at the fuel pump module must show battery voltage for ~2 seconds, then drop to zero volts. Both black wires must show less than 5 ohms resistance to ground at all times. Check it out and post your results.

[Mic1980]

Thank you for the response Old Master, when you say the fuel pump module do I have to check right at the connector? or can I check at the splice with the wires connected? because when I checked the voltage on the grey wire it wasn't connected and it was constant voltage. Thanks Boss

edit: I was thinking isn't it safe to assume that the fuel pump module shuts off after 2 seconds because when I turn the key I can hear the fuel pump prime for 2 seconds, what do you think?

[old_master]

Best to check voltage and resistance right at the fuel pump module connector. That way you know that power and ground are being supplied the module. Ideally you should check it right at the pump motor, which would test all wiring and connectors.

When you initially turn the ignition to the RUN position, the PCM activates the fuel pump relay for ~2 seconds. During that time, (pump prime) if the PCM does not receive data from the crankshaft position sensor, (which it won't because the starter is not turning the crankshaft) it deactivates the fuel pump relay. When the ignition is in the START position, the fuel pump relay is activated continuously.

Probably ought to check fuel pressure and leakdown at the service port. Key ON, engine OFF, fuel pump running: pressure must be 60psi to 66psi and must remain above 55psi for at least 10 minutes after the pump shuts off.

This fuel delivery system, (CSFI) must have correct fuel pressure to start & run properly. Aftermarket pumps don't make the grade. Fuel pumps are no different than anything else, you get what you pay for. If you want a pump that will work properly, and last, you need an AC Delco or Delphi pump. They are typically in the $180 range.

[Mic1980]

Ok that sounds like a plan. I did see a AC Delco sending unit module for $90 on ebay but it wasn't the whole assembly if I had seen it before I would have grabbed it.

[old_master]

Get it diagnosed first, then make a decision.

[Mic1980]

I will I'm going to stay with what I have but if I would have saw that AC Delco first I would have bought it before the one I got. The pump is definitely pumping fuel I just have to see if it's pumping enough to get to 55-61 PSI. So that means I need to purchase a fuel pressure tester, maybe a harbor freight one.

[Rick Norwood]

Originally Posted by Mic1980

So that means I need to purchase a fuel pressure tester, maybe a harbor freight one.

I bought one from Harbor Freight and it is o.k. I think I paid $15 - $20 for it. However, I wouldn't swear to its accuracy. I would certainly try one. Keep your receipt and if you find that the gauge is inaccurate, take it back and get a refund.

[old_master]

Originally Posted by Mic1980

I just have to see if it's pumping enough to get to 55-61 PSI...

1996, (CSFI) fuel pressure spec is 60psi to 66psi, (key on, engine off, fuel pump running). If it's less than 60psi, you will have problems.

[Mic1980]

I swear to God I saw 55-61PSI yesterday on my alldata now it says 60-66psi oh well anyways I checked for voltage and it it read 11.45 volts while the pump was priming and it then stopped after 2 seconds. I also checked for resistance it was reading from 0.03 to 0.04 ohms at the connector on the grey wire. It was definitely pumping fuel as well so I'm headed to go get a fuel pressure tester.

[old_master]

On 1995 and older CMFI systems, fuel pressure spec is 55psi to 61psi. If pressure is too high or too low on either system, it will cause problems. If you want to be sure you have correct information, you need the (manufacturers) factory shop manual. All Data is a much better choice than Chilton or Haynes, but aparently they make mistakes too.

Make sure the black ground wires show less than 5 ohms to ground at all times.