View Full Version : Intermitent stumble (fishbite)
Two days ago I started having issues with DaHoooley.
It started stumbling and missing horribly then as quickly as it did it it was fine.
NO CODES.
All the grounds and such are fine.
Now we all know that intermitent gremlins can literally drive one to drink.
This seemed to be possibly a fuel supply issue BUTTTTTTTTT???
I decided to check the items that are the nastiest to fix out on the road.
I replaced the Oil pressure switch and then ripped the old one apart.
It had long seen better days and replacing it was good.
The fuel lift pump looked to be the factory original so to the can it went.
Again I ripped into this too and it had issues. The check valve was leaking and the innards were well used and had seen a lot of crap go through.
Another item best fixed now and not along side the road in the dark.
The PMD is always a suspect on these trucks as far as I am concerned even if the issue is the tail lights. :D (Just kidding)
I did however get the chance to buy one of the Dtech replacements and it is now doing the honors.
After all this I drove the truck to town and all seemed well, but after about 5 miles I got 4 quick "fishbites" fast quick misses and then smooth again.
Hmmmm drive the beast back to the ranch and ripped the air plenum off to get some room and replaced the Optical sensor filter harness with a fresh one.
The truck ran fine the rest of the day. I took it for a 60 mile romp and got it up to and maintained about 90mph on a good stretch of road that has no access for 4 miles.
Ran like a top and no more hicups.
These filter harnesses can and do go south. Our local pump shop recommends a fresh harness on any new pump unless the harness has been replaced recently.
The OPS, Fuel pumps and all these little things can and do go south over time.
This system is so complex and there are so many things all having to work in harmony with each other that one little gremlin can just really mess it up and not leave much in the way of diagnostic tools to work with.
I hate replace and try tech but sometimes one has little choice when the issue is an on and off thing.
Anyone with a high mile 94-95 would be wise to think about a fresh filter harness if your getting any little stumbles when running down the road.
The Oil pressure switches on the 94 and 95 are vulnerable to failure due to the fact that they hold all the power to run the lift pump.
The fuel lift pumps are pre filter and see every bit of crap that the filter ultimately sifts out including water. They will only do it so long before the go away.
These items are all fairly easy to replace on a nice day in the sunshine but a real booger on a rainy night in the cold.
Just some insight into what I found and what was probably some prudent replacement of parts.
I will however state that I am not crazy enough to proclaim it all fixed for at least a week or so. then maybe we will party. :rolleyes:
Later troops
Robyn :D :D :D
Artworks
10-27-2007, 06:03
I was having same trouble awhile ago, and just removed the Optical sensor filter 'harness' . Things have bin going fine exp for last week when I got SES light on set code 62 ( first thout it to be 26 duh!) and ran like c-ap, couldn't get it off, but with help of the pages, found out that the connector going to the little black box sensor on the intake (MAP ? ) had become disconnect ! Is there any issue I should watch for with running without the Optical sensor filter harness ?? Thanks for all your info & the rest here for there input. I would have had to put out many $$$$ and pulled a lot more hair out ( don't have much left anyway LOL ) if not for everyone here at The Pages. Next rounds on me !
I am not fully up to speed on exactly what all these magic electronics do exactly or why but its is my understanding that the Optical sensor encoder on some pumps can get fussy and the engineers fix was to install the RF filter harness to block stray impulses.
Mine first started it Tuesday eavening and at road speed in 4th lockup it was a very violent jerking and bucking.
If your truck runs fiine without the filter it will be ok.
It was a bandiad me thinks to fix an issue that popped up from time to time on some rigs so the solution was to install it as a running fix all.
I believe that the 96 and later trucks do not use this and the filter is handled by the ECM.
I had a lengthly discussion about this very topic last eavening on the phone with Jim.
My truck seems to be fine now.
The Map sensor becoming unplugged will cause a code for sure.
If the little clip that holds the plug in becomes broken you caqn thread a zip tie around the sensor and through between two of the wires on the plug and snug the tie up and this will keep the plug where it needs to be.
Mine is this way.
I did recently buy a new wiring harness for the engine to fix all the mess in there.
The harness that lays under the intake in the valley feeds the IP and most all the sensors on the engine except oil pressure and temp sender for the gauge.
Its about $250 but well worth the $$$ if yours is getting thrashed.
Having a clean new and nice harness is a good thing and can eliminate a lot of worries and or sources of issues.
I saved the one off my 94 as it was in good condition and I may use it on the DaHooooley instead of the new one
Later and good luck
Robyn
Robyn,
When I had a similar problem with my 'burb it ended up being a chaffed wire on the harness near the turbo, apparently being chaffed by the heat shield and was not obvious. The only reason it was found is because the tech at Liberty Chevrolet (thanks to JoeyD to pointing me in that direction) had seen it before.
Interesting
I cant think of any wires over on that side of the engine that could cause any issues.
The main harness that runs the IP and all the sensors is under the intake manifold.
The only wires that are by the turbo or even close are the glow plug wires and these wont affect the running of the engine once it is started.
Can you be more specific???
Thanks
Robyn
I just checked my truck to be sure I remember correctly. On my '98 'burb there is a major wire loom on the firewall behind the right side of the engine and in looking at that I can see how if the loom was loose the back of the heat shield could rub on the loom and possibly chafe and short a wire. However, when I was talking with the mechanic he noted that in my truck it was only doing it occasionally because the wire was only grounding on occasion based on the position of the wire relative to something to ground on it. I think that the wires that run under the intake are contained in this loom, and from what I can see it looks like this is the major harness coming through the firewall from the computer (I think my harness was fixed by replacing the harness from the computer, but I would have to double check my paperwork to be 100% sure on that). Also if your Dahooley has AC the pressure switch harness for the dryer comes out of this loom. Since this has been repaired I have put a about 1500 miles on the truck w/o any trouble.
My 95 has loom on the RH rear and indeed the AC wiring does come from there.
If all is proper the harness should be held up well with calmps so it does not rub on things.
The harness under the intake plugs into the main harness with a couple very large multi pin plugs that clip to the bracket that is on the fuel filter.
I have a new wiring harness for the engine and will change it eventually but not right now.
I am still working on a Horton fan clutch setup for the truck and when I tear into things Im going to yank the radiator, water pump and crossover as well as the turbo and fix a bunch of little crap while im in there.
Oil drain tube hose at the lower end of the turbo drain leaks a little and when I do the Hiflow water pump and dual stat Xover a few other things will get done too.
Good time to swap out the old wiring and generally police the area up.
Robyn
My harness over time had apparently lost a clamp and was rubbing, but agreed if all was in order it should not have been rubbing. However, with the age of our trucks and who know who has been under the hood over time (unless owned since new) it is something to keep in mind. A Horton fan clutch? Is this one of your class VII adaptations? I am curious why you would go with this and not a Kennedy clutch or something similar? Is it electrically actuated?
trbankii
10-29-2007, 10:06
A "stupid newbie" question of a sort after reading this and your "oil pressure" thread - but I get the impression that these are issues for the "electronic" engines as opposed to the "mechanical" ones?
I haven't exactly become "intimately" familiar with my truck quite yet, and still sometimes am left wondering if something applies to me and I should check into it...
Thanks!
Robyn,
I read in one of your other posts it sounds like you fixed your problem by repairing the harness. How much of it did you replace, and did you find the location of the problem?
trbankii
I think this would only apply to the electronic engines but I have never played with a mechanical one.
Hi all
The oil pressure thread can and does apply to all 6.5 factory installed engines that do not have a mechanical lift pump.
Any DS4 equiped truck will fall into this catagory.
The 92-93 6.5 TD trucks also have the same OPS system with the electric lift pump.
All the trucks back many years have a sending unit that feeds the gauge and they can and do get flakey.
THE FISHBITE issue is peculiar to the DS4 only
The fix apparently was the filter harness. This is a little small wiring harness about 6" long that plugs into the upper rear of the IP and then right into the main engine wiring harness along side the IP.
This little creature has a rectanglular black box in it that the wires run through.
The function of this device is to filter unwanted electrical noise from between the optical sensor and the ECM.
When these go bad the truck can run real poorly with stumbling and what is called Fish Bite.
The symptoms could be compared to a gasser with a plug or plugs that are misfiring.
The harness is easily reached by removing the air plenum from between the turbo and the intake manifold.
Another area of concern on these engines is the main engine wiring harness that lies under the intake and feeds the IP as well as all the engines major sensors (CTS, IAT, MAP ect)
This harness if time has not been kind or if its been unplugged during a rebuild and the connectors violated in some way can be a source of issues.
Also this harness lays in the valley and is subject to vibrational wear and if there has been fuel leakage this can take its toll.
The main harness is about $250 but worth every penny if you are doing a rebuild and the one on the engine is looking poorly.
*** A note here***
Most all the weather tight plugs on these harnesses are available as a "pig Tail" from GM that can be spliced into the original wiring.
So many other plugs are available for the underhood wiring as well as other places around the truck.
FAN CLUTCH
I am not very happy with the operation of the viscous drive fan clutches.
Mine is near new by what I can see of it and still the engine temp must get to near 230F before the fan will come on and pull good.
The radiator looks to have been replaced about 2001 according to the date stamped in a yellow ink on the tanks.
The "Horton" unit I am working with is for the T444E Navistar as used in the business class trucks such as medium duty tow trucks ect.
The clutch was designed to rotate the same as in the 6.5 and it was designed to handle a larger fan.
The stock steel fan from the 95 6.5 TD will bolt right onto the Horton.
The advantage of the Horton is its an electric direct drive coupling and is actuated by a water temp switch as well as a High side pressure switch on the AC system as well as a manual dash switch.
IMHO after running class 8 stuff for years and always running my fan manually during hot weather (Turn it on and leave it on especially on a hard pull) is that having the ability to engage the fan before the engine gets cooking hot and then let the stats open at 180F will keep the heat issue well under control.
The viscous drive fans will only run at about 85% of shaft speed due to internal slippage so there is a loss right there.
The Horton unit required the modification of the HO water pump to accept the Hortons thread on hub.
I removed the drive flange from a Power Stroke pump (T444E) and swapped it onto the 6.5 pump. (The water pump shafts are the same size so its a press one off press one on thing)
Next I modified the 6.5 drive pulley so it fit the pilot on the new flange. The bolt holes are the same so that was not an issue.
The wiring is very straight forward. (1) switched hot lead to feed the sytem (1) set of leads goes to the dash switch and one set to an A/C high side switc and a ground
The last set of leads goes to the temp switch that will be positioned in the RH head at the top rear blockoff plate using an adapter from a 6.2 head. ( nice hot spot)
The temp switch is set for 215 F but can be purchased in many different temps to suit the application. (On at 215 off at 185)
Under normal driving the fan will sit idle and when either the engine temp or the AC pressure dictate the fan will spool up and do what is needed.
When pulling hard when towing or in slow hot driving the fan can be turned on and left to run.
Just my idea of how things should be.
Installed properly its a very fool proof setup that will not only please the discriminating diesel buff but will handle the chores by itself when Mom and the kids are out to the grocery store.
This system is identical in function to what we see on almost all class 8 rigs.
The only exception is that this clutch is electromechanical instead of air.
I wanted an air unit that I could run with a small electric compressor but Horton has stopped making them.
I hope to get this all together on DaHooooley this spring.
The Horton is all fit to the 6.5 pump and I now have a dual water crossover so when I get some time I will yank things apart and do the swap.
I have several other minor repairs that I wish to complete while Im under the hood so when the time is right I will do it all and clean up some "P O" messes that were left behind.
Overall the Horton should show some fuel savings as it will be shut off most of the time when driving at road speeds and during cooler weather.
The advantages of having more complete control are many and I think obvious as how many times have we wished we could cool it off faster than the factory unit allows??
Also the Horton setup has less rotating mass when the fan is turning as the bulk of the weight of the unit does not turn but is the floating coil assembly that is attached via a flexible strap to the engine.
Best
Robyn
93GMCSierra
11-04-2007, 13:39
Robyn do you have a pic or 2 of the horton assembly, I understand the concept you are talking about but I really would like to see the way it would go together.
here are some pix of the assembly as it sits right now.
I still have a little work to do on the thing but its minimal.
The white strap is to hold the armature assembly stead under running conditions.
You can see that the GM fan sits right on the pilot and studs just like it was supposed to be there.
The large hex nut on the clutch screws onto the water pump flange that was transplanted from the Stroke water pump.
Now this Clutch will not screw onto the later GM 6.5 pump with the thread on clutch. :(
The GM unit uses a different size threaded hub.
Horton only makes the one CCW rotation clutch and it was for the T444E so that is why I made the choices I did.
They used to make a lot of different units but the market was too fickle and according to their people it was far to expensive to try and keep up with big boy companies that did not care.
This clutch is available from Horton and a used water pump from a 7.3 is easy to find and press off the hub.
The metal fan from the 92-98 6.5's will drop right on the hub and the nylock nuts come with the clutch.
It aint cheap either. the clutch assembly is about $600
Then one needs to either buy a good used pulley to modify or as I did a new one.
I little fooling around will build some fixtures to hold the new pump and allow the flange to be R&R'd
The wiring harness and such comes with the clutch.
The unit functions like an A/C compressor clutch but is just beefier and designed specifically for the application.
The RPM ranges and fan speed on a stroke are about the same as the 6.5 so its a good swap.
Hope this answers your questions
Robyn
86DuallyCrew
11-14-2007, 22:43
Robyn, when you were getting the fishbite was your truck throwing any DTC codes? I am throwing a DTC 35 and the only symptom I ever have is the fishbite. I have read some conflicting reports that it can/maybe/sorta/kinda/might throw a DTC 35 code. Other causes for the 35 apparently are PMD and air getting to the optic sensor (ie. air leak between lift pump and IP)
I had absolutely nothing going on accept the engine ran like crap (missing) and then just stopped doing it. Then again in a few days it did it again.
No codes at all.
The truck has been running flawless since I replaced the fitler harness.
The other items I replaced needed replacing just as a matter of preventive maintenance.
The DTC 35 is an injection pulse width error and can be related to the fuel solenoid or possibly the ECM itself.
A poor connection of the wires at the fuel solenoid can cause this too.
I would say try a filter harness but if codes are setting (35) then it very well may be time to get the IP off and freshened up or just replace it.
If you can get a scan tool on the beast then you can watch the pulse width as the engine is operating and the issue will be quite clear. Possibly not exactly why but it will show it.
***** A Note*****
My 94 Burb would toss 35's on ocasion when I was running the SOL D unit in place of the regular PMD. This leads me to believe that YESSSS a failing PMD might cause the 35 to set.
Swapping out the PMD is always a good thing if in doubt. Key element here is that usually the PMD's will just work or the wont, BUTTTTTTTT there have been wierd ones too.
I bought a DTECH replacement for DaHooooley and its doing the deed now, we shall see.
Robyn
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