Leaky Injectors

[L29er]

hey there so my 98 gmc K2500 7.4l has a issue with hard starting when warm, it did this a couple years ago and it was just the fuel pressure regulator, now its doing it again, so i changed the pressure regulator again, no fixy, have a pressure testing gauge and reads 55psi running, i think spec says 60 or something, i don`t have any drivability problems. What is the rate of pressure loss in relation to time lapse that says injectors are bad, it stinks of gas when it eventually does start and black smoke. i`m probly gonna pull the upper manifold and visually inpect for leak down but since i have a gauge it would be nice to gaurentee they fall below holding specs, is it like 10psi per half hour or something,?...thanks

[cammiller]

That is a known problem with the 7.4L. I have done several sets of injectors for that reason. I have even done the same truck a year later and they were leaking again. Easy enough to change.

[L29er]

That is a known problem with the 7.4L. I have done several sets of injectors for that reason. I have even done the same truck a year later and they were leaking again. Easy enough to change.

 

 

well they just lost 10psi in half an hour, does that conclude it must be injectors? i`m gonna pull the upper intake off tommorow and visually see, i`m also wondering the possibility of it being the crank sensor? getting alot worse, hard to start after even 10 minutes now, ideas? starts good after 4-5 hours sitting...thanks

[cammiller]

No, the real test is to power the fuel pump with the upper intake off. Reach in and see shich ones are leaking, however, I would bet money it is the injectors.

[tmcmahon]

What else?

 

I have a 1998 7.4L Suburban and it has the hard warm start issue as well. But recently while replacing the lower intake manifold gaskets, I replaced the fuel pressure regulater, had the injectors cleaned and tested (all tested OK), cap and rotor (because I was there). It still has the hard warm start problem. I still need to find someone to set the distributer timing. I sure wish they still used timing marks and a timing light.

 

The truck only has 74k miles.

 

Any ideas what I should check next?

[L29er]

What else?

 

I have a 1998 7.4L Suburban and it has the hard warm start issue as well. But recently while replacing the lower intake manifold gaskets, I replaced the fuel pressure regulater, had the injectors cleaned and tested (all tested OK), cap and rotor (because I was there). It still has the hard warm start problem. I still need to find someone to set the distributer timing. I sure wish they still used timing marks and a timing light.

 

The truck only has 74k miles.

 

Any ideas what I should check next?

 

 

um when they tested your injectors they didn`t leak down? i just installed some bosch injectors instead of the gm ones, they are less than half the price and so far they are running perfectly, and also your ingintion timing is not adjustable, its computer controlled.

does your truck smoke when it does start?, mine was really noticable. do you know what your fuel pressure is?

one way i gaurenteed it was injectors was to shut the truck off warm and go under the hood and depressure the fuel line at the port, (then i stunk like gas but...) then when i went to start it like a half hour later turned key on let fuel pressure come up and it would start easy every time, when i did finnaly do my injectors when i took the intake off i was almost overcome by gasoline fumes, dude it was bad,.... anyways letme know about my earlier questions, later...

[tmcmahon]

As for the timing distributer adjustment, the specs I found shows the distributer should be adjusted to:

TEST PROCEDURE

The ignition timing cannot be adjusted. The distributor may need adjusting to prevent crossfire. To insure proper alignment of the distributor, perform the following:

1. With the ignition OFF, install a scan tool to the DLC.
   
2. Start the engine and bring to normal operating temperature. IMPORTANT: Cam Retard Offset reading will not be accurate below 1000 RPM.
   
3. Increase engine speed to 1000 RPM.
   
4. Monitor the Cam Retard Offset.
   
5. If the Cam Retard indicates a value of 0°+/-2°, the distributor is properly adjusted.
   
6. If the Cam Retard does not indicate 0°+/-2°, the distributor must be adjusted.
   

(Unfortunately my cheap scan tool doesn't show Cam Retard values)

 

No noticable smoke on start up.

Engine off fuel pressure is 60

Leak down tests on injectors all passed (The injector shop was surprised - he warned me of there high failure rate, he even told me to expect a couple to fail)

 

I'll have to try the dump the fuel pressure trick and see if that makes a difference.

 

Thanks for the feedback