Intermittent Fishbite Continues

[CedarGrove]

98 K3500. Rebuilt Reviva installed in Jan. About 3 weeks ago I had a couple of no start situations when the motor was hot. Replaced the batteries (1 was toast). Also had intermittent fishbite type stumbles every now and then. Would also flat line just going down the road without warning. I could pull off the road, put it in park, restart and keep going. It did this about twice a day for 2 days. Had code p1216. Parked it while a new D-tech pmd was being shipped to me. Installed the PMD (and resistor from old PMD) on wednesday. Fishbite continues. No stalling or hard starting issues yet. Pulled code P1216 yesterday. Cleared the code and did a test drive with scanner plugged in. Had the fishbite stuff going on but no codes were set. Replaced the ignition switch today and fishbite continues. Lift pump is kicking out fuel with engine at idle. Motor does not stumble when I open the valve. Put 5 psi on the tank and left it for about an hour. No diesel smell anywhere and no drips. I don't think it's an air in fuel system issue. Problem happens with full tank or empty tank. Looked at wiring coming out of computer at firewall near the turbo. Nothing seems out of whack there. Checked the grounds from engine to chassis and chassis to cab. All seems good.

I'm stumped. Anyone think the 5521 is going tits up? I'm just gonna drive it tell it pukes. I'll recheck the codes next week and see if the p1216 comes back.

What say ye?

Lewis

[Hubert]

Fishbite is a really tough one. At what speed and rpm does it happen? Could be transmission related or .....

Have you read heath's log on the electronic filter harness between IP and wiring harness?

But again fishbite is hard to diagnose so try and find consistency in when it happens. Can you notice any fuel differences? Precise fuel metering can cause drivability issues due to fuel quality. For some reason my truck did not run so well on one local truck stop but a big chain and don't know why for sure. Regionally fuel comes from the same refinery but different fuel distributors treat fuel differently. Also tank maintance regimes are different. But if Cedar Grove is a small town many stations may be using the same distributor. Try and see if any correlate.

[CedarGrove]

The filter harness is MIA. Removed at some point by a PO. I replaced the optical sensor back in January. It pooped out a couple of days after the new engine was installed.

I can generally make it stumble 7 out of 10 times at around 3000 rpm if I punch it hard. I don't spend much time up that way. I feel it mostly under light throttle in the 1700 to 2000 range.

I think I'll double check the plug at the optical sensor.

I just can't sort out if it's an electrical issue or if it's the pump. Those 2 things are so intertwined on these trucks. Major headache sorting it out. Love the truck, hate all the head scratching and throwing parts at it.

I'll keep driving her till she pukes, then I'll probably throw a rebuilt pump at it unless y'all have any ideas.

Cheers,

Lewis

[CedarGrove]

I should also mention that the stumble will sometimes knock off the cruise control.

Lewis

[bl78ljb]

I would look hard at the wiring going to the pump, especially the optical sensor, and also consider the OPS (oil pressure switch) and if that was swapped off the old engine a new one wouldn't hurt just to eliminate that and JK has a relay to isolate that from the load to drive the lift pump (it is possible that the lift pump works intermittently causing the problems if the OPS is on its way out). Just some thoughts.

[Turbo Al]

I would definately by pass the oil pressure switch (hot wire it to run the fuel pump)and take it for a run and see what happens. Mine did the stubble thing for a while there and it was a flaky OPS. These motors run fine up to 1,800 to 2,000 (mine anyways) without the help of the fuel pump -- the injection pump is doing all the work.

Al

[CedarGrove]

The stumbling has continued. I unplugged the optical encoder sensor, just to see what would happen. No fishbite at all with it unplugged. It's hard to start when it's unplugged, the ses light stays on, and I'd say the power is off a bit, but no stumbling.

I just replaced the optical encoder sensor in January. Why would it whack out again so soon?

Lewis

[Hubert]

I don't know specifics but thought when you unplug the optical sensor the PCM goes into some kind of default mode (nominal timing fuel rates etc).

This happens after so many cycles of starting and not cranking up hence the long cranking.

Anyway maybe the default settings covers up the fishbite and is low on power and not necessarily indicative of bad optic sensor??? I further guess a bad optic sensor would set a OBD code usually maybe not always???

[Hubert]

Read a blurb on it and yes it goes into limp mode. My understanding the PCM commands a set solenoid closure time and retards timing.

Setting a set solenoid closure time would definately mask fishbite in my mind. As I think fishbite is a problem with precise fuel metering. And or if this isn't dumb sounding but a conflict between solenoid timing control, PCM, optic sensor, and IP cam timing all combined with timing chain wear and precise timing measured desired vs actual. Timing and fuel rate metering really are what control the smooth RPM control.

I would guess w/o noise filter the PCM defaults to some avg to compensate for but with a good noise filter it better averages the real world reading and allows it to compensate for real timing of the IP and solenoid open / close to control precise fuel metering.

Dang I have typed this reply a couple of times and can't figure out how best to get my thoughts across. Anyone want to comment along those lines.

[CedarGrove]

Hubert,
Thank you for the response. Now break it down for me...What do you think the next move might be? 'Nother optical sensor encoder? 'Nother pump?

Lewis

[JohnC]

I have nothing to back this up, but I'm guessing the optical filter is to protect the outside world from the optical sensor's signal, not to protect the optical sensor's signal from the outside world.

If the PCM has a problem with the optical sensor it'll log missed counts.

[Hubert]

Lewis,

I fully admit I don't know what causes fishbite. And don't want to suggest any expensive parts replacement.

And this level of electronics is beyond me. John if the noise filter protects the outside world and not the inside world then its still has a use. Maybe it helps protect the FSD signal to the PCM or vice versa or to solenoid itself. Still stands to reason fuel metering fishbite (if that's what it is) is still a problem with precise fuel metering and its related electronic and or mechanical control.

Not that this helps much but ....
I think GM's diagnosis ended there. If it limps ok and or if it solves an issue unhooked but bad hooked up then GM says replace the IP :-(. Which I am not suggesting just that it relates. Later I think they also said to always replace the noise filter with a new IP. Hmmm ???

[JohnC]

...if the noise filter protects the outside world and not the inside world then its still has a use. Maybe it helps protect the FSD signal to the PCM or vice versa or to solenoid itself.


I was thinking AM radio....

Unplug the optical sensor. If the problem goes away I's a good bet the sensor is bad. Or put a scanner on it and look for missed counts.

[Robyn]

With the disconected Optical sensor stopping the fishbite I would start to think about either the PCM being flakey or the IP has issues internaly.

If the fuel solenoid is getting hinky and it is operating in a sporadic fashion this could certainly cause the issue.

If you can beg borrow or steal another PCM and try it you might be able to eliminate one possibility.

Do you have access to a good scan tool?
It would be great if you could watch whats going on in the system when the fishbite is happening.
Watching real time events on the scanner can often pinpoint issues rather than trying to guess.

Many codes will not set if the issue is sporadic and does not fault long enough to allow the PCM to catch on to whats happening.

Good luck and keep at it. You will beat this.

Robyn

[CedarGrove]

Hey y'all. Thanks for sticking with me on this one.

A couple of things...There is no optical filter on this truck, never was as far as I understand it. When I say I unplugged the optical encoder sensor, I mean I totally unplugged it...I'm running in limp mode.

I spoke with Bill Heath on the phone today and he was totally helpful, informative, and friendly. He wants to know what the fuel pressure is and what my TDC offset is. Also wants me to triple check my electrical/ground connections. My gut feeling is that it's another optical encoder sensor gone south, but Bill wasn't buying it.

I'm gonna keep chugging with it. I should have pressure numbers and offset numbers tomorrow night.

Anyone have a line on an optical encoder sensor?

Thanks for the input.

Lewis

[Robyn]

The later trucks with OBD2 did not have the filter harness as it was built into the ECM. The harness or the filter circuit in the ECM serves to filter out induced noise from outside sources that could compromise the signal from the optical sensor.
This signal is a very low voltage and it is critical that the signal be clean otherwise there can be issues. (what you have)

I still think the best way to aproach this is to get a scanner on the truck and get some real time data running on the screen and watch whats going on during the time when the "fish are biting" :eek:

With some real time data to work with you should be able to discern the problem without buying a buttload of new parts you dont need.

Best

Robyn

[Hubert]

The later trucks with OBD2 did not have the filter harness as it was built into the ECM. The harness or the filter circuit in the ECM serves to filter out induced noise from outside sources that could compromise the signal from the optical sensor.
This signal is a very low voltage and it is critical that the signal be clean otherwise there can be issues. (what you have)

Robyn, I could be wrong but I think all trucks had the "noise filter" inline from the factory. The PCM is different for the OBD-I vs II. And I think the later trucks were less prone to the issue. Maybe better board level stuff I don't know???

I looked real quick in my helm manual as I thought I had seen it but didn't see it this AM before work. Also, I vaguely remember getting a quote for the part through gmpartsdirect. Again, I thought they had a part number for my '97 but could be confusing it with another quote. I'll look again tonight.

[CedarGrove]

Robyn,
I did the real time thing last month without much luck. It wasn't throwing codes on the bites. I usually check the codes every week or so and P1216 is always there when I check. I cleared it and went for a ride around the block (10 miles) with the scanner hooked up. Nothing.

I did notice that my cruise control did not seem to work with the scanner plugged in if that is worth anything.

BTW...Fuel pressure is looking good. 6 psi at idle, 5 going down the road, 4 when I have my foot in it towing a small trailer.

I'll try to score the offset numbers this weekend.

Cheers,

Lewis

[Robyn]

If you are not getting any codes popping up while the fish are nibbling then whatever it is is not irritating the computer.

Are you sure there is not any air passing through the system??

I am pretty sure the OBD2 units had the filter built into the ECM and did not use the harness.
I seem to recall that the harness was only used for 94-95 units :confused:

Does the fishbite lessen if the throttle is backed off some when it starts??? and or does it worsen if more throttle is applied.

My DaHoooooley will do this but only when the fuel tank is below 1/4 and it is actually sucking air though the bypass valve in the tank.

Now the P1216 is fuel solenoid response time too short.

You could have a flakey Fuel solenoid in the IP or possibly even a PMD thats going south.

I am fairly certain that the code is related to the fishbite.

This has got to be a fuel delivery related issue.

Hmmm another thought. Is the little ground wire from the PMD harness still hooked to the IP?? if not get it back on the pump.

Some remote mount setups spec out connecting the ground wire to their new cooler.

The ground needs to be on the pump.

Also be sure you are getting a good 14V or more to the junction box feed.
These things dont like low voltage.
Poor ground cables will also drive them nutsoid too.


Best

Robyn

[CedarGrove]

I'm gonna throw a rebuilt pump at it. I'll let y'all know what happens.

Lewis

[CedarGrove]

Hello all,
I threw the rebuilt pump on yesterday and things seem very good so far. I'll feel better in a month if everything stays stable, but so far so good.

Ran the koko routine to set the timing and things seem reasonable with a -.61 offset.

I'm hoping this solution sticks because changing a pump is a real pain for me. Lots of work with lots of room for error.

The truck seems to be a bit peppier than it was on Monday, so I am pleased.

If anyone wants a hinky 5521 sans pmd, it's yours for the postage.

Thanks,

Lewis

[Hubert]

I am interested PM sent.

[ttpost]

Sorry dont mean to sound dumb, but i have never heard of fishbite before, what is it thanks rob

[Hubert]

The severity differs greatly but one description is a subtle chug of the truck while cruising. It kinda feels like a small fish biting a live bait but not catching the hook. Kinda a little quick chug chug chug surge or buck you feel in steering wheel, throttle pedal, and I guess seat too. Again kind of like the truck is a big fishing pole. Its a drivability quality issue mostly.

[ttpost]

thanks, i kinda thought it was something like that. i just had a similiar problem, the fuel filter cap was a little loose that solved it. thanks again rob

[CedarGrove]

Just a quick update to let everyone know that I am very pleased with the rebuilt pump and everything seems great these days. I towed about 10,000 lbs today for about 80 miles. EGT pre-turbo did brush 1050 for about 20 seconds while getting on the highway. ECT never pushed past 210. I feel like I was about on or over the limit of what the truck wanted to do, but she pulled through and did what had to be done. A good day all around.

Interestingly...Most days my wife drives the truck, pulling a small enclosed trailer. She gets 12 mpg. Today I drove 180 miles. 80 with an empty 14 ft gooseneck dump trailer, 80 with 7000 lbs of lumber in the trailer, and 20 without anything. I get 12 mpg.

Cheers,

Lewis

[ttpost]

I had something interesting today, truck #2 which we just got started dying and fishbiting, died several times, bled the system out and jumped the lift pump, no luck just kept getting worse every mile i drove. i coasted into the gas station and it ran fine after i filled it up. it showed almost a HALF A TANK when i pulled into the station. i assume it either has holes in the p.u. or to gauge is off. but it was interesting and i just thought i would throw that into the thread. rob

[Hubert]

I had something interesting today, truck #2 which we just got started dying and fishbiting, died several times, bled the system out and jumped the lift pump, no luck just kept getting worse every mile i drove. i coasted into the gas station and it ran fine after i filled it up. it showed almost a HALF A TANK when i pulled into the station. i assume it either has holes in the p.u. or to gauge is off. but it was interesting and i just thought i would throw that into the thread. rob

Was it instantaneously better. Or did it take just a bit - minute or 2. That would be hard to differentiate unless you have a poor idle quality. You very well could have a tank-sock-pick-up tube issue. Fuel delivery definately been linked to drivability issues such as fishbite bucking etc.

Or it could have been fuel quality and fuel metering performance too. Good fuel mixed with some marginal fuel will make good fuel depending on contaminates or lubricity etc. I have a variable amount of something like "clutch chatter" on launching in 2nd gear. It varies mostly by fuel differences. Just last week I filled up with some fuel that caused poor smoothness performance. The truck ran a bit rougher and launching nice and smoothly was difficult. I dosed the tank with fuel additive and 2 cycle oil and within just a few minutes launching was much smoother again. In my case fuel level did not change. Thats why I believe it can be a precise fuel metering issue also. My thinking here is either dry or crappy fuel is not as easily metered especially with an aging IP or timing chain and/or aging injectors (probably all compound on the issue).