Hard start

usmcdevildog73

Original poster
Member
Mar 29, 2022
9
CA
Good morning everyone. I have a 2004 Suburban. 5.3l. I recently replaced upper manifold gasket. All connections appear good. New knock sensors, new oil pressure sender. Cleaned injectors, tested to see if they ran well. Put everything together, started her up and boom....hard start. Took 3 cranks to start. Primed fuel pump, started right up. Tested fuel pressure...read 36psi. No drop in pressure after a few hours. Replaced fuel pump ( integrated fuel pressure regulator and filter). Started up...hard start...one crank only this time. Baffled. Checked fuel pressure again...46psi. Not as low as before but still low. Thinking bad ground or defective pump. Thoughts.... it's a Delphi pump
 
Last edited:

Dr.Fiero

Member
Dec 7, 2017
161
S. Alberta
Good morning everyone. I have a 2004 Suburban. 5.3l. I recently replaced upper manifold gasket. All connections appear good. New knock sensors, new oil pressure sender. Cleaned injectors, tested to see if they ran well. Put everything together, started her up and boom....hard start. Took 3 cranks to start. Primed fuel pump, started right up. Tested fuel pressure...read 36psi. No drop in pressure after a few hours. Replaced fuel pump ( integrated fuel pressure regulator and filter). Started up...hard start...one crank only this time. Baffled. Checked fuel pressure again...46psi. Not as low as before but still low. Thinking bad ground or defective pump. Thoughts.... it's a Delphi pump
Is it 46 while running, or is that during cranking?

I know it’s hard to get to, but check the voltage right at the pump during crank.
 

usmcdevildog73

Original poster
Member
Mar 29, 2022
9
CA
Is it 46 while running, or is that during cranking?

I know it’s hard to get to, but check the voltage right at the pump during crank.
That's right at turning key without starting. Yeah I'm dreading dropping the tank down to check for voltage. Sucky thing is I didn't have this issue prior to removing the intake. Could a surge have occurred once I reconnected power and made fuel pump relay go wonky?
 

TollKeeper

Supporting Donor
Member
Dec 3, 2011
8,047
Brighton, CO
Any MIL/Check Engine codes?
 

TollKeeper

Supporting Donor
Member
Dec 3, 2011
8,047
Brighton, CO

Dr.Fiero

Member
Dec 7, 2017
161
S. Alberta
Try swapping the fp relay with another in the box?
It’s not the ecm driving the relay or it’d never run!

Have you 100% confirmed spark during the hard start? Do you get tach movement during the no start crank?
 

usmcdevildog73

Original poster
Member
Mar 29, 2022
9
CA
Try swapping the fp relay with another in the box?
It’s not the ecm driving the relay or it’d never run!

Have you 100% confirmed spark during the hard start? Do you get tach movement during the no start crank?
I'll swap the relays. I'll be changing the spark plugs today since it's due however what baffles me is the lower fuel pressure. A bad spark would it cause lower fuel pressure wouldn't? What do you mean by tack movement?
 

Dr.Fiero

Member
Dec 7, 2017
161
S. Alberta
I'll swap the relays. I'll be changing the spark plugs today since it's due however what baffles me is the lower fuel pressure. A bad spark would it cause lower fuel pressure wouldn't? What do you mean by tack movement?
Swapping relays will just rule out slightly crappy contacts. You should see tach movement during crank (2-400rpm). If you don’t, I would start looking at the cam sensor wiring since it’s up top in the area you were in. It’s TINY (!) gauge wiring and can break if farted on too hard.
 

usmcdevildog73

Original poster
Member
Mar 29, 2022
9
CA
Swapping relays will just rule out slightly crappy contacts. You should see tach movement during crank (2-400rpm). If you don’t, I would start looking at the cam sensor wiring since it’s up top in the area you were in. It’s TINY (!) gauge wiring and can break if farted on too hard.
I'll check it out again I did swap that out when that out when I replaced the other sensors and the gasket since I was there already I figured I would replace it with a brand new one. I replaced it with a delphi sensor
 

Dr.Fiero

Member
Dec 7, 2017
161
S. Alberta
I'll check it out again I did swap that out when that out when I replaced the other sensors and the gasket since I was there already I figured I would replace it with a brand new one. I replaced it with a delphi sensor
Not so worried about the sensor - it’s the harness. One good hard tug can internally snap a wire. It’ll look fine, but it’s broken (or partially broken) inside the insulation.

I’ve gotten pretty good at sticking my thumbnail into it and sliding along. Can feel if there’s a break. But that’s an acquired thing!
 

Dr.Fiero

Member
Dec 7, 2017
161
S. Alberta
Got a scope by any chance? Borrow one?

Be nice to back probe at the ECM to see if the cam & crank signals are getting through, and that they're clean.

Then while it's running, move the harness around and make sure it stays steady. Needless to say concentrate on the area you were working!
 
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