High Idle "Hic-Up/Fishbite"

[DennisG01]

Now that the cold weather is here, I've got a little fishbite thing going on. When warming up the truck, with either of the high-idle's engaged, the engine will fishbite for about 1 or 2 minutes (might happen about 20 times within that 2 minutes). If don't engage the high idle, it will not happen. This only happens if the truck has been sitting long enough to get good and cold.

I just wanted to pick your guys' (and gals' :smile5 brain a bit. My thought is probably a bad ground issue or the connection into the ECM. Does that sound right?

Also, does this fishbiting hurt anything? It's a split-second each time it happens.

 

[Dieseldad97]

Yaknow Dennis, mine will do that every once and a while also. Mine usually while I'm doing highways speeds when it's cold. I'm interested where this thread will go.

 

[Turbine Doc]

Did you do an optic bump at some point ?

 

[DennisG01]

No, I have not done an optic bump. Just a re-flash.

 

[96 OILBURNER]

Do you notice any smoke when this happens? The reason I ask, is because I am having a similar issue. I put a hair dryer on the IP and one on the FFM for about an hour Friday and it did not do it, so I am going to experiment some more today.

 

[DennisG01]

Smoke? Maybe just a little tiny, tiny, tiny, tiny bit. It's white smoke - just like a normal, cold engine produces in cold weather. I'll try to take a little better look next time.

Temperature wise, I'd say this only happens around 30* or so and lower.

 

[jmiller]

I've seen the same behavior. For me its been worse at 1600, seldom does it at 1100. Once it warms up, its fine.

Since I'm down for a rebuild, I'm making sure the little things are well taken care of, like clean the last of the grounds.

 

[schiker]

What is your normal fuel and or additive?

My typical fine fuel metering issues: shutter on launch and fishbite, are best correlated to fuel. Some station's tank maintenace additives just cause poor fine fuel metering for me. I quit the 2 cycle in favor of non detergent sae 30 plus periodic cleaners for maintenance Opti-lube and Stanadyne preferred but sometimes power service if out because its convienant only.

Could also be a voltage thing. See where your voltmeter is at during episodes. After the initial starting drain it might take 2 min to get back up to 13.8 +/- volts. Cold weather is a bit worse for this. Double check passenger pos post. Why it might only do it on high idle may be faster fuel metering solenoid speed and need for power (good 12V) ????

Have you checked your lift pump operation lately. Could you have gotten bad fuel to accelerate pump wear (specifically the fuel solenoind plunger)?
How many miles on IP and "new" engine?


Where is your PMD/FSD located? Original on pump? And its age?


Not sure fishbite is really bad except for the extra wear and tear of uneven roughness and might cause cummulative long term wear and tear on engine mounts and front main hub and serp belt etc. Just maybe block stress but with your 18:1 splayed should be tough enough. Can't really think of any other problems it might cause.

 

[Dave01]

I'd suggest you put a fuel pressure gauge on it before the cold start, then start and watch your fuel pressure. If at high idle you see the pressure drop you may have a weak lift pump. Also, how long since your last fuel filter change? A partially plugged filter can cause fish-bite. Once the filter is warm it will flow fuel better.

 

[kane]

Two years ago I tried to get the fish :mad2: out of my sub by changing cables (also fuel solenoid cable), checking grounds, PMD, marine injectors etc all that is always listed by people... finally... it's gone... and the last I recall I did was the play with optic bump. Since that... no fishbyte 1 1/2 years...
It did usually on highway, driving OD ~1800-2000rpm, little uphill = more torque/fuel supply with OD on... it made once or twice. Then again 100 miles or more... no byte... It was not bad but of course I had my thoughts always on that... why?
Happy now

 

[schiker]

Fishbite for sure is a tough one to nail down with a specific cause.

I can see an optic bump making some timing difference for light fuel and pcm periodic adjustments.
Could an electrical connection at the optic sensor cause issue or moving and "bumping" the sensor cause it to work better or clear some trash or align it better????
I can see anything that affects fine fuel metering causing issue so the optic sensor is a possible issue.

Just devils advocate a guy over on the page had fishbite and tried several things and iirc he did replace the optic sensor with no success . I took that IP a part and the optic sensor looked OK (no electronic test just visual so very basic test). It was tight on the cam ring is really all I can say for sure. Anyway a new IP fixed his fishbite. The fuel solenoid plunger was worn on that one and it was older. And he had some sporadic issues with code 36 iirc ????

When he unplugged the new sensor it did not fishbite. When you unplug the optic sensor it sets a default time or default fuelrate adjustment or something that I think will mask fishbite (from fine fuel metering issues). So the optic sensor does relate somehow pretty significantly.

 

[DennisG01]

I always get fuel from one of two places - they seem to move their fuel quickly. I also always use a generous amount of FPPF Total Power. Got about 9K on new engine. Maybe 15K on the current IP. Filter was changed about 1K ago. Haven't hooked up a pressure gauge to LP recently, but it also has about 15K on it.

I'm going to try some of the suggestions you guys mentioned.

If I'm understanding you guys correctly (and infer a little bit), I *think* I can negate a fuel or supply problem by simply holding the throttle elevated manually? If all checks out, that would lead back to something specifically with the high-idle switches?

If I start the truck w/o high-idle engaged (and let it do it own "high-idle"), there are no problems.

The last two morning when I started the truck with the high-idle engaged, it didn't do it - it acted normal.

PS: Thanks for the info about whether or not the fish-biting is bad for the engine. I was sort-of thinking along the same lines (although not nearly as specifically as you stated), but it's nice to hear it from someone more "in-the-know" than me.

 

[schiker]

If I'm understanding you guys correctly (and infer a little bit), I *think* I can negate a fuel or supply problem by simply holding the throttle elevated manually? If all checks out, that would lead back to something specifically with the high-idle switches?

Not necessarily fuel delivery to IP is always a suspect for generally any drivability issue including fishbite. The IP has to have an excess of fuel delivered or wear and tear is accelerated on internals. The excess fuel cools and lubricates the IP. If you don't create an air leak any where the IP can pull enough fuel from the tank to run decently if filter is clean but again will shorten the life of the IP over time. I think I have finally gotten to figure out inside the IP is a rotary vane pump called the transfer pump that moves fuel inside the IP. It has enough suction to pull from tank but adds stress to the IP again because it likes to be over fed freely the correct temp of fuel. I am still trying to learn more about this internal spill - fill - return circulation. The IP has some nifty balanced or biased checkvalves mechanisms.
???I think it likes somewhere between 40F and 120F for No. 2 fuel likes 60-70F fuel best I think???.

Your fishbite sounds more like a fine fuel metering issue (the fuel delivery to the injectors). Its either caused by delivery to the IP but more likely an electrical issue or mechanical metering issue. The PCM controls idle and finely adjusts metering. The amount of fuel to idle or up to ~2000 rpm with light to no load is so small it takes very fine adjustments to be smooth. Holding the throttle still above idle takes away some of this PCM control of metering but the fuel has to be balanced smooth metering or you'll get fishbite again due to an electronic or mechanical issue.

Also forgot not that you have to worry about it but it would also stress the clutch disc from variations of pulses and associated torsion through drivetrain. But I would think an automatic could soak up these better.

 

[DennisG01]

OK. I'll keep going with my "diagnostics" :rolleyes5:

Just to be clear - this fishbite has only ever happened while under High Idle.

I started the truck up an hour or so ago. Even though the temp has gotten up to the mid 40's, it started to fishbite with the H.I. So, I immediately flipped it off and held the throttle on manually. It stopped doing it. But, when I flipped the H.I. back on, it still acted good (no fishbite). I suspect that this was a just a timing thing and since the weather was warmer, it was only going to do the fishbite thing for a few seconds, anyways.

I pushed/wiggled/tugged at the individual H.I. wires that go into the ECM. I pulled the H.I. ground wire off and verified it was connected solidly into the ring connector. Cleaned the area, then re-attached. By the way, I have it grounded to that big metal bar that runs left-to-right behind the dash (about knee height).


Fuel Flow PSI (lift pump):

I've been thinking about purchasing an inexpensive gauge to use for temporary diagnostics. If I recall correctly, do I connect it to the outlet of the fuel drain? Last time I did this was about 4 years ago and I just taped the gauge to the bottom of the windshield so I could see it while driving.

Any suggestions for a gauge? Or, at least, what I should be looking for in a gauge... or what to avoid?

 

[schiker]

Nothing over 15 psi at full pressure. You want easy to read resolution at usually about 3-6 psi on fuel pressure at IP depending....

Should do basic lift pump check with water drain its easy. Quick test and should be ok for ruleing out lift pump. A pressure test is best based on if gauge is Tee'd in at IP inlet. Water drain will tell you if you have pressure from lift pump but filter could be clogged and have pressure drop. I am pretty sure water drain is on dirty side of filter. I don't think the filter is your problem though otherwise you would get other issues too. But a bad lift pump might be culprit until rotary vane transfer pump gets good prime and flowing.

I suspect a fine fuel metering issue /timing adjustment from electronic or mechanical issue. Big help with diagnoses I know ( I do what I can :smile5.

Anyone want to post what these might be other than optic sesnor? Since it only happens for first few minutes could it be a little air at fitler manager or leak down of internal pressure or injector leak down or bad LP?????? Idle control would control both sides of rpm but foot on throttle is more one sided that might mask this fishbite correction???? Wild guess.

 

[DennisG01]

A pressure test is best based on if gauge is Tee'd in at IP inlet. Water drain will tell you if you have pressure from lift pump but filter could be clogged and have pressure drop. I am pretty sure water drain is on dirty side of filter.

OK, just repeating what you are saying to make sure I understand correctly:

If I get good pressure at water drain, then LP is definitely good.

If I get bad pressure at water drain, then a dirty filter could be skewing the readings and the LP could be good, or bad. Further investigation would be needed.

 

[NVW]

OK, just repeating what you are saying to make sure I understand correctly:

If I get good pressure at water drain, then LP is definitely good.

If I get bad pressure at water drain, then a dirty filter could be skewing the readings and the LP could be good, or bad. Further investigation would be needed.

Dirty filter will have no effect on pressure at water drain. It would have an effect if pressure is taken before IP by a Tee in the fuel hose.

 

[Dave01]

The reason I'd like to check fuel pressure before looking into IP or other issues is that it's simple to do and it has caused fish-bite for me before. In my case it was a dirty fuel filter causing pressure drop under load. You can get a pressure gauge from Harbor Freight, or an auto parts store, or I think Heath Diesel will lend you one (charge for it then credit you if you return it).

Your comment that it only happens with high idle but not under load on the highway makes me think there is probably more to it, but I still like eliminating the simple stuff first.

 

[schiker]

OK, just repeating what you are saying to make sure I understand correctly:

If I get good pressure at water drain, then LP is definitely good.

If I get bad pressure at water drain, then a dirty filter could be skewing the readings and the LP could be good, or bad. Further investigation would be needed.

Good pressure test at water drain does confirm LP is good. But doesn't confirm IP has good supply pressure because the filter could be restricting flow to the IP (and its starving for fuel). To nail down just a bad filter (and good LP) you'd have to 2 guages and figure the differential pressure across filter. But one gauge satisfies me as long as the IP is happy I am happy. If I loose supply pressure to the IP inlet I'll then test water drain flow to check LP is working. If ok I can change filter or find a bad LP or other problem between tank sock and IP inlet etc.

 

[DennisG01]

I'm going to get a pressure gauge and do some checking. Like mentioned above, if for nothing else to eliminate this aspect.

It seems as though I can find 2" gauges readily (good point on the 0-15psi!!!:smile5. The only larger one I can find is the one (Span) that Heath carries. This seems like a good tool to have, so I'd actually like to just purchase one, but of course still keep the cost reasonable. I think the 2" might make it tough to read while driving.

Unless anyone knows of a larger gauge, I'll probably end up with the Heath gauge.

Thanks for all the help so far guys! I'll post back when I have some more info.

If I don't post again before the year's end, Happy New Year to you and yours!