Lift pump issue

biged681985

biged681985

Arklahoma Bombers
Joined
Mar 12, 2008
Messages
306
I have a customers truck. Brought it to me because it was hard to start sometimes, and the lift pump was not coming on. I'm diagnosing the issue, the lift pump comes on by telling it to with the scanner. The pump does not come on by turning ignition to run, and will not come on when you bump the starter. Soon as the truck starts, the lift pump runs and is pushing 17-18psi at idle. Any help would be appreciated. 870-405-5419


Codes it had but did not come back driving it down the road
P0234
P0230
P1689


Code it had before and after clearing codes
P0215
 
There was a TSB on hard starts many years ago that set the truck up to NOT run the pump until the engine is running. In hot conditions these trucks would basically vapor lock causing really hard starts. VP trucks are known to have hard starting issues that are not consistent.
 
Given how old this thread is..... If you're still trying to address this problem with your customers truck then post back and I'll do what I can to help you pin point the problem.

These 2nd gen ISB trucks dont generally have "random" starting issues and will most always follow a specific patter which easily distinguishes what the cause is. :Cheer:
 
Haven't messed with it lately. Truck runs fine besides lift pump not coming on till after truck is started. I'm supposed to get with them and have it flashed at the dealership just haven't had a chance yet.
 
Without knowing any details about what its doing.....this is what it should be doing.

When turning the key to the ON position, the fuel pump should prime cycle for 2 seconds.
When turning the key to the ON position and only "bumping" the starter with the key over in the START position, the fuel pump will cycle for 25 seconds.

Cranking the engine to start, the voltage from the ECM to the fuel pump will alternate on/off in order to reduce fuel pressure by approximately half.

As soon as the engine starts and runs, the voltage to the fuel pump will be constant 12 volts as the pump runs continuously.

If its not doing anything just said then there may be an ECM issue or the connector from the ECM to the fuel pump is no longer getting voltage signals. Not terribly uncommon as people have found that they have to wire the fuel pump to another hot source with a ignition triggered relay. No ones really sure why the ECM can do that either but its either corrosion, loose connection, or voltage load too high and destroying that particular circuit.

But if all above is working and:

If the engine experiences a hard start when the engine is cold and has been sitting (like overnight) then its most likely a fuel leak causing the prime to be lost. The extra cranking is merely re-priming the fuel system.

If it hard starts when the engine is at operating temp and temporarily shut off but doesnt want to re-start easily, then there's possibly two reasons.....
1) The PSG solder is crystallized from excessive heat cycles and fuel pressure too low.
2) If there is an aftermarket fuel pump on the truck then the fuel pump is too aggressive and is placing too much fuel pressure on the VP during engine cranking, even with the alternating voltage.

There are a couple other reasons based on the trucks condition and current setup, and having a fuel pressure gauge in cab or test gauge will help too. So maybe you can make something of that info but let me know what you find out. :Cheer:
 
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Some good points made here. I had this same problem for some time and didn't know why. I finally made the decision to run a Smarty and every since then the lift pump has been cycling normally. Although lately it has become slightly delayed. Turn key on, wait 5 seconds, then lift pump cycles for 2 seconds, then it starts like normal.
 
On a side not, because its worth pointing out..... These 2nd gen ISB trucks are VERY sensitive to electronic anomalies and anything out of spec can potentially cause phantom issues having you chasing your tail. Therefore, its very important to make sure both batteries are in perfect condition and of the same age and size, all cables and connections and grounds are tight and free from corrosion, and the alternator is not generating excessive AC noise which disturbs other electronic components.
 
turn key on, it doesnt run pump for 2 seconds. bump starter the pump does not run for 25 seconds. start truck lift pump runs, building 16 psi at idle, 14 at wot. batterys are older but clean, no issues there. can run the lift pump with KOEO using my snap on solus.
 
Without getting rash and assuming the worst first..... Try investigating all the relays and fuses.
I know this may seem odd but I cant stress enough how electrically intertwined these engines are. :Cheer:
 
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