• Welcome to The Truck Stop! We see you haven't REGISTERED yet.

    Your truck knowledge is missing!
    • Registration is FREE , all we need is your birthday and email. (We don't share ANY data with ANYONE)
    • We have tons of knowledge here for your diesel truck!
    • Post your own topics and reply to existing threads to help others out!
    • NO ADS! The site is fully functional and ad free!
    CLICK HERE TO REGISTER!

    Problems registering? Click here to contact us!

    Already registered, but need a PASSWORD RESET? CLICK HERE TO RESET YOUR PASSWORD!

What's wrong with my Suburban?

6.5TD Burb

6.5TD Burb

Member
Messages
133
Reaction score
3
Location
Wendell, NC
I have an intermittent "fish-bite" that will NOT go away. Newly rebuilt injectors and IP (IP from Pensacola Diesel), new PMD, just got back from putting in a new (reman) ECM, OPS is fine and it's got a relatively new LP. Comes at any throttle amount and at one point I could tell you where/when it would do it. Any ideas?
 
If this is on your 94 in your sig I'd suspect ops. But I would put a fuel pressure guage on it and see what it reads too. Could also be air
 
did you replace the electronic filter harnes on the IP? it doesn't come with the New IP.

(Copied from another site)
A failing filter harness can set codes 17 and 18. It can cause stalling after startup, hesitation and occasional 'fish byte' missfire ( one solid miss that commonly occurs at medium throttle).

It is best to not take chances with the old filter harness---replace this with the updated unit.
The filter harness plugs into the optic sensor at the top-rear of the fuel injection pump. It is about 7" long, connecting between the optic sensor and the main engine harness.
 
Oh yeah, forgot about that. That one is a relatively new Delco unit. Came with the piece that screws into the injector pump too (don't know what that one is).

Oil pressure reads fine and normal, cold and hot. Both hoses from the filter manager to the IP have been replaced.
 
The oil pressure sending unit controls the lift pump after it starts. If it fails the lift pump won't run but the guage will still read normally.
 
That's what I don't get: if the gauge reads right how the LP won't work.

I got the part that the LP works through the OPS, dad and I have had discussions on that.

Is there any way to know without having to actually replace the OPS?
 
The contact that run the guage are sperate from the guage part of it. You should be able to test for power out of it. But easiest would be to open the t valve while running.
 
The OPS has a contact and separate wire from the pressure reading gauge wire for the lift pump. This contact burns up and will only carry voltage but no amperage. You can get 12V at the lift pump connector, but plug in the lift pump and the voltage goes to 7v. The other 'ops' wire goes to the pressure sensor assembly that lasts longer than the lift pump contact.

So the OPS can be "It's half dead, Jim." vs. "It's dead Jim."
 
ak diesel driver said:
The contact that run the guage are sperate from the guage part of it. You should be able to test for power out of it. But easiest would be to open the t valve while running.
Click to expand...

WarWagon said:
The OPS has a contact and separate wire from the pressure reading gauge wire for the lift pump. This contact burns up and will only carry voltage but no amperage. You can get 12V at the lift pump connector, but plug in the lift pump and the voltage goes to 7v. The other 'ops' wire goes to the pressure sensor assembly that lasts longer than the lift pump contact.

So the OPS can be "It's half dead, Jim." vs. "It's dead Jim."
Click to expand...

Well that makes sense.

Every time the valve is open while running it runs a good few psi (haven't thrown a gauge on it yet). Guess it's "do or die"....I'll pick another one up at work tomorrow.
 
You might try a short time running w/ the fuel tank cap loosened - and see if it makes any difference.

The theory being any place in the pre- lift pump plumbing that might be occasionally sucking in a bit of air, would be less likely to do so, with no tank vacuum.

Not the end-all, be-all of diagnostic tests, but pretty easy to do & I've heard of one example where it did show a difference that was tracked back to a loose fuel feed hose clamp.
 
Well took the fuel tank cap off on the way to work, inconclusive. Put it back on at work but not till it clicked....it's "snug". It had a small fishbite on the way home but nothing that I would say solved or helped yet. Do have another OPS on standby though. I guess I'll find out about the sock when I do the body swap. I honestly don't think it's a sock as before I started driving it only on weekends I could tell you exactly when/where it would do it and only for a couple seconds; but at this point I'll check anything.
 
Open the t-valve when engine is running. See if you can get fuel to come out. If not, the LP has issues.

Next, try to jump the LP with 12V source, there is a direction in the FAQ. If you can start and get fuel to come out of the t-valve. You have a working LP but not necessarily working OPS. So replace the OPS, get an ACDelco OPS and not the store brand.

A little clarification, the gauge that you read is the oil pressure gauge on the dash. It is not the fuel pressure. We don't have a fuel pressure gauge in this truck unless you put it yourself. You can put the pressure gauge on the t-valve outlet and open the t-valve to measure the fuel pressure.

Another thing, if you have a new IP but non-working LP system. Your IP will have to suck fuel all the way from the tank. That is a No-No. It will ruin your IP.

Read up on the LP/OPS thread in sticky FAQ above this section of the forum.
 
Yeah the filter harness is on the vehicle. AC Delco unit, that was put on/replaced this past summer.

I haven't opened the valve in a while but when I do to eliminate possible problems I never have any problems with getting a good stream out of it. I can hard wire the lift pump and hear it working; I will admit that I haven't got to put a gauge on it yet to measure pressure though. I do need to do that. I hope it's not the LP, it's not that old. I do have a fuel pressure gauge waiting to be installed it's just too cold to do it...snow doesn't help either (finally getting some!) :D
 
You must log in or register to reply here.
Back
Top