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Tractionless 08-15-2017 07:21 AM

Help Chasing Erratic Idle Please
 
1996 7.4L LX Mpi, 263 hrs., SN OF886167, all OE, raw water cooled. Wouldn't idle upon purchasing the boat and was told IAC was bad. Replaced IAC (it came out in pieces) and it idled per spec for a few trips. Around the same time the VST was rebuilt, fuel filter changed, oil and filter, plugs, cap, rotor and wires, fuel tank pickup checked and clean, 90* fitting into mechanical fuel pump clean, tank to pump hose changed.

The last 4 trips the idle began getting erratic again. It started with surging when bringing the throttle up to 1000 rpm for a couple of trips. That was also followed by the inability to idle on the hose immediately after pulling from the water and i had to keep it going with the throttle, I can hear the IAC whistling during this. Now the last 2 trips idle is at 1100 rpm in the water but immediately after it won't idle on the hose still, I can still hear the IAC whistling. Just before the last trip the manifolds were changed so there shouldn't be any water leaking into the cylinders.

I scanned with the Rinda Codemate prior to my last run and got "coolant sensor low" and "TPS high" codes on a cold engine and not running. Problem is the 2nd motor runs just fine and I got the same codes out of it 2 minutes later. I know, I know scan it, right?! I've been trying for months with 3 different options in town and keep getting kicked down the road. One is at Merc. And they have no idea when it's coming back. Another says they're 10 days out, want the boat today and want to charge me storage for each day they're not working on it until they get to it (laughed in their face). And the third always has an excuse of why he couldn't keep our appointment.

If anyone knows of a shop on Florida's Treasure Coast who can scan MEFI ECU's, I'd be happy to give them my business. In The meantime if someone could take a shot in the dark at what may be causing my idle issue, I'm all ears.

Thanks for any help you can lend
Keith

F-2 Speedy 08-15-2017 07:42 AM

maybe your chasing a vacuum leak

SB 08-15-2017 09:02 AM


Originally Posted by Tractionless (Post 4576051)
1996 7.4L LX Mpi, 263 hrs., SN OF861319, all OE, raw water cooled. Wouldn't idle upon purchasing the boat and was told IAC was bad. Replaced IAC (it came out in pieces) and it idled per spec for a few trips

Ran your S# but it comes up as an outdrive serial #. You sure that's the engine serial# ?

buck35 08-15-2017 11:10 AM

I found a paper tag on mine back by the coupler. The one on the ecm box was warn and unreadable.

AllDodge 08-15-2017 11:38 AM

2 Attachment(s)
You can scan for codes with a paper clip and a resistor 12V LED (radio shack), but sounds like your new IAC has gone bad.

Trash 08-15-2017 12:42 PM


Originally Posted by F-2 Speedy (Post 4576055)
maybe your chasing a vacuum leak

Concur.

Tractionless 08-16-2017 06:38 AM


Originally Posted by SB (Post 4576084)
Ran your S# but it comes up as an outdrive serial #. You sure that's the engine serial# ?

Sorry typo. Here's the correct. OF886167. I edited the OP as well.

Tractionless 08-16-2017 06:40 AM


Originally Posted by AllDodge (Post 4576130)
You can scan for codes with a paper clip and a resistor 12V LED (radio shack), but sounds like your new IAC has gone bad.

As described in post #1 I scanned with a Rinda codemate and didn't receive an IAC code. The codes I did receive are posted in the OP.

airjunky 08-16-2017 12:24 PM

Make sure the yellow and black wires going to the coolant sensor have not deteriorated and shorted out , and you have a crisp 5v ref voltage to tps and ect. No green funk in ecm connectors

Tractionless 08-17-2017 03:23 PM


Originally Posted by F-2 Speedy (Post 4576055)
maybe your chasing a vacuum leak


Originally Posted by Trash (Post 4576159)
Concur.


Originally Posted by airjunky (Post 4576445)
Make sure the yellow and black wires going to the coolant sensor have not deteriorated and shorted out , and you have a crisp 5v ref voltage to tps and ect. No green funk in ecm connectors

I'm thinking along the same lines as Airjunky or bad temp. Sensor. If it was a vac leak I feel the idle issue would be of the same kind (unable to run OR high idle) at all times and not so random. Hell maybe I'm wrong, but that's why I asked the community for assistance. I'll check it all.

Keith

BUP 08-17-2017 03:30 PM

scan tool really is needed and would like to know how the past owner knew the IAC was bad. These IAC are the GM style that do not go out like what ecm 555 and pcm 555 uses. Yes they do fail these GM IAC but its like 2 out of 10 compared to 555's in which is 9.5 out of 10 for failures

Volvo Penta very currently still used that GM IAC and I rarely see it fail.

Tractionless 08-18-2017 06:22 AM


Originally Posted by BUP (Post 4576762)
scan tool really is needed and would like to know how the past owner knew the IAC was bad. These IAC are the GM style that do not go out like what ecm 555 and pcm 555 uses. Yes they do fail these GM IAC but its like 2 out of 10 compared to 555's in which is 9.5 out of 10 for failures

Volvo Penta very currently still used that GM IAC and I rarely see it fail.

I'm trying with all my might to get it scanned, you wouldn't believe the run around I've gotten from the shops. Latest was last weekend when I was told to call at 9 AM Saturday, no answer until 1 PM then I was told he was working on an emergency trailer job, call back Sunday at 1 PM. Called every 15 mins. From 1PM until 3 PM Sunday and kept getting the answering machine. That doesn't even count the months leading up which I was trying to get it scanned for hours and rpm log. .......and that's my best lead on getting it scanned.

The mechanic doing the pre-purchase survey told me. As described in post #1 it came out in pieces. I can hear it whistling when trying to keep it running on the hose so I doubt it is the culprit this time.

Keith

Tractionless 08-21-2017 11:53 AM

I used CRC 656 and a toothbrush to clean the small harness side connectors. The ECM harness was pristine.

Today I tested the ECT for 5v, it's good. I replaced the ECT for good measure as well. For $17 it's not worth testing the temp. range on a stove top.

I tested the TPS harness side per the manual as well and when I got to "hook a test light to battery + and then touch the light to blue wire on the harness side connector, does it light?" it did not light and flow chart says replace TPS. Again for $39 w/lifetime warranty I'm in the middle of replacing it as well.

During the key on procedures above I can hear the IAC whirring away for a couple of seconds. At least it sounds like it's still in on piece. IAT harness tests good as well and I cleaned the sensor with MAF cleaner.

After 10 hrs. Installing new trim tab hoses and locator system and doing the above didn't have time to start the engine to see what if any change I made.

After setting the new TPS to 0.7V at idle last night the engine idles (cold) on the hose at the correct rpm and without any issue. The real test will be after being out on the water then flushing to see if it will stay running or not. Hopefully this weekend if the weather holds up.

Keith

Tractionless 08-31-2017 07:35 AM

Following up wih the last paragraph of the above post.

Fail on idle again at the ramp. Fired it up and it was pouring out black smoke and idling at 1100 rpm. This is after running perfectly on the hose last week, no changes were made. I checked the new tps and it was at 0.7v as tested above. Swapped MAP sensors and it was no better. Code reader got "TPS high" and "coolant temp. Low" and would not clear them. I tried adjusting the TPS value down and it wouldn't net below 0.6v at idle, put the old TPS back in and set to 0.58v (lowest it would adjust) which netted clean burning exhaust and 600 rpm idle. Codes still read "tps high" and "coolant temp low" Took the boat out and around 1k rpm it still surges (TPS value stays steady) . Put it back on the hose to flush out (at the ramp) and idle was steady at 600 rpm.

Short of trying another IAC (current has less than 20 hrs on it) or swapping ECU's I'm out if ideas.

As stated by others above the scan is desperately needed while on the water and the issues are present to see what is happening with all sensors etc. at the same time. I guess I'm not going to solve this on on my own.

AllDodge 08-31-2017 08:21 AM

2 Attachment(s)
Suggest checking connections to IAT, MAP, ECT and TPS and note the common ones

Tractionless 09-01-2017 06:46 AM


Originally Posted by AllDodge (Post 4579789)
Suggest checking connections to IAT, MAP, ECT and TPS and note the common ones

Checking as in with a multi-tester as per the manual (non-scan) approach? I've done all but the MAP and they were fine. Will check MAP next. Thanks

Warship2k15 09-01-2017 07:00 AM

Check all your grounds after that.And clean them all even if they look good.

Warship2k15 09-01-2017 07:10 AM

One more thing.I have seen iac sticking after just a short time.

If the old one was sticking and you still have it I have cleaned them and then used teflon lube in one's on other vehicles and it lasted many years.Remlube is what we had at the time.

Never tried it on a merc one thats why i suggest the old one.

Just an idea for a cost effective fix.

Warship2k15 09-01-2017 07:13 AM

Oops just saw the old came out in pieces.

Tractionless 09-20-2017 01:45 PM


Originally Posted by Warship2k15 (Post 4580017)
One more thing.I have seen iac sticking after just a short time.

If the old one was sticking and you still have it I have cleaned them and then used teflon lube in one's on other vehicles and it lasted many years.Remlube is what we had at the time.

Never tried it on a merc one thats why i suggest the old one.

Just an idea for a cost effective fix.

Been on a small hiatus since being affected by Hurricane Irma but getting back into working on this issue.

Where do I apply dry teflon lube? Shaft that screws in and out? I have a new IAC coming (I'll lube that on too) and while having the TB off I'll wokr on getting the TPS more closely adjusted to 0.48 as advised.

I spoke with MEFI Tuning who suggested making sure the TB fully closes which I'll do but highly doubt it's the issue with 268 hrs. Then they advised to swap ecu's between engines.

Keith

Tractionless 10-22-2017 07:38 AM

Installed a teflon lubbed new IAC motor yesterday, TPS still set at 0.58v, fired up on the hose and it ran rough (like a dead hole(s)) blowing black smoke and idling at 1100 RPM.

From previous info. given above; with the old IAC and TPS at 0.58v it ran fine on the water, no black smoke but wouldn't stay running on the hose and idle surged on the water. Additionally when the TPS was set at 0.7v (manual value) it ran exactly how it did in my opening sentence when I fired it for the first time on the water; however, ran fine on the hose. When I brought the TPS value down to 0.58v on the water it didn't smoke, idled at 600 and purred like a kitten, now back to rough running, high idle and blowing black smoke.

ECU's get swapped next.

Warship2k15 10-22-2017 09:53 AM

Did you check your meter for acurracy or try a different meter.
You could also hook up the the other rod and see what it's reading now.
It could definitely be the ecu.
But you don't want to be chasing your tail because you have a meter that started acting up.

Tractionless 10-22-2017 10:45 AM


Originally Posted by Warship2k15 (Post 4589334)
Did you check your meter for acurracy or try a different meter.
You could also hook up the the other rod and see what it's reading now.
It could definitely be the ecu.
But you don't want to be chasing your tail because you have a meter that started acting up.

Oh yea, 3 multi-meters all reading the same thing. Being I get the same (idling) results with multiple IAC's, TPS' (at varying voltages), water temp. sensors, MAP sensors and after verifying all connectors are receiving and providing the correct "info"; I'm going to see what I get from swapping ECU's today.

On car platforms I've seen issues with ECU's on the fritz causing intermittent issues.

Tractionless 10-22-2017 06:35 PM

I first confirmed the good running engine TPS is the same voltage as the erratic running unit 0.57V. I prefer to compare apples to apples but read on.....................

As promised, ATTEMPTED to swap the ECU's today and happened upon MEFI 1's with two different Model numbers. The erratic idling #16234539 and #16189069 on the other engine that has zero issue. See attached picture, they are different sizes. I stopped right there as I'm not sure whether or not they are swap-able. The #162 (erratic engine) was used by Mercruiser the #161 was not and seems to be a GM car/truck ECU (see attached picture from MEFI Burn). So now I have more questions than answers.

Should the Non-Mercruiser unit (#161) even be on a boat? Did modifications to sensors, harness, tune etc. need to be made to use in on my engine? I was afraid of swapping them and potentially cause more harm than good.

https://uniim1.shutterfly.com/ng/ser...714842/enhance

https://uniim1.shutterfly.com/ng/ser...714862/enhance

Keith

AllDodge 10-22-2017 07:14 PM

Don't know right now but might have found the issue so long as the ECU was not re-flashed. Need to look more indepth

Trash 10-22-2017 10:28 PM

See my reply in your other post...

Tractionless 10-23-2017 01:33 PM

I called MEFI Burn today with the issue. They stated any of the model numbers of MEFI 1 will work but must have the correct tune installed. MB also stated the MEFI's were used in other platforms other than the marine industry. If I have to purchase another unit I'll need to ensure its loaded with the proper mapping for my engine, no matter what the model number.

Atleast I now know I can swap side to side and see if my issue goes away. Hopefully the weather will hold up to do it after work tonight. Then I'll know if I need an ECU or the problem is somewhere else in the harness in which case I'm buying a scanner.

Tractionless 10-24-2017 07:27 AM

Swapped ECu's and no change, still idling at 1100 rpm, blowing black smoke and running rough.

Switched back to original ECU, unplugged the TPS harness to tape the exposed insulation (used during testing) plugged it back into the TPS, decided to start the engine again and VIOLA; idles at 750 rpm, no smoking and not running rough! Then I blipped the throttle and right back to running rough, blowing black smoke and idling at 1100 rpm?!!?

Normally I'd assume TPS going bad; however, I've already experimented with a new TPS, set at the same base voltage as the OE unit and it had the same rough running, blowing black smoked and idling at 1100 rpm issue. See post #14. The harness side at the TPS has been tested as well, see post #13.

I feel I'm out of options and I ordered scanning software from MEFI Burn before writing this post.

Warship2k15 10-24-2017 07:54 AM

Wiring harness bad?Fuel injectors bad?

SB 10-24-2017 08:58 AM

May have missed it...what is your fuel psi when running good vs running bad ?

F-2 Speedy 10-24-2017 09:30 AM


Originally Posted by SB (Post 4589734)
May have missed it...what is your fuel psi when running good vs running bad ?

didn't you calk about the VST in some cases flooding the plenum in another thread.....but I've slept sense then.

Tractionless 10-25-2017 07:36 AM


Originally Posted by SB (Post 4589734)
May have missed it...what is your fuel psi when running good vs running bad ?

Haven't checked as I verified good fuel pressure prior to this issue. I'll go back and see where it stands now. Thinking fuel pressure regulator?


Originally Posted by F-2 Speedy (Post 4589742)
didn't you calk about the VST in some cases flooding the plenum in another thread.....but I've slept sense then.

VST was completely rebuilt 15 hrs, ago.


Originally Posted by Warship2k15 (Post 4589728)
Wiring harness bad?Fuel injectors bad?

I checked the harness at all the sensor connectors earlier in the thread, all came out well. I'll see what the scanner software I have coming nets prior to pulling injectors.

On a lighter note, I've gone from being very frustrated to excited to find the gremlin and solve this very random issue. Wish it wasn't costing me so much time out on the water though and time away from other smaller projects.

Keith

Trash 10-25-2017 11:12 AM


Originally Posted by F-2 Speedy (Post 4589742)
didn't you calk about the VST in some cases flooding the plenum in another thread.....but I've slept sense then.

That wouldn't apply to this situation. The VST plenum flooding comes into play after a warm engine has sat for a period of time allowing fuel to percolate out of the aged VST internal diaphragm thru the yellow hose and into the plenum. Having said that its good to bring up and cover all the bases.

Trash 10-25-2017 11:15 AM


Originally Posted by Tractionless (Post 4589719)
Swapped ECu's and no change, still idling at 1100 rpm, blowing black smoke and running rough.

Switched back to original ECU, unplugged the TPS harness to tape the exposed insulation (used during testing) plugged it back into the TPS, decided to start the engine again and VIOLA; idles at 750 rpm, no smoking and not running rough! Then I blipped the throttle and right back to running rough, blowing black smoke and idling at 1100 rpm?!!?

Normally I'd assume TPS going bad; however, I've already experimented with a new TPS, set at the same base voltage as the OE unit and it had the same rough running, blowing black smoked and idling at 1100 rpm issue. See post #14. The harness side at the TPS has been tested as well, see post #13.

I feel I'm out of options and I ordered scanning software from MEFI Burn before writing this post.

Can you replicate the poor idle / normal idle issue by fiddling with the TPS connector or its associated harness? One of the pins might be suspect.

Tractionless 10-26-2017 08:32 AM


Originally Posted by Trash (Post 4590006)
That wouldn't apply to this situation. The VST plenum flooding comes into play after a warm engine has sat for a period of time allowing fuel to percolate out of the aged VST internal diaphragm thru the yellow hose and into the plenum. Having said that its good to bring up and cover all the bases.

Yep, no issue with hot restarts.


Originally Posted by Trash (Post 4590007)
Can you replicate the poor idle / normal idle issue by fiddling with the TPS connector or its associated harness? One of the pins might be suspect.

Thought about that after packing it up the other night. I should have the scanning software this weekend and will check the harness (fiddling) as well as fuel pressure and bring up sensor diagnostics etc. all at once.

ICDEDPPL 10-26-2017 05:50 PM

If you`re chasing an erratic idle problem I`d recommend better shoes and/or some endurance training.
It may be tough at first but once you catch that erratic idle, it will be well worth it and you will feel a great sense of accomplishment.

Tractionless 10-31-2017 08:10 AM

Dorman (CTI) P/N-84598, TPS harness has corrected the 1100 rpm and blowing black smoke idle on the hose on cold startup.

I'll have the boat on the water this weekend with a scanner to see if it's still going to idle surge and die on the hose during flushout. Stay tuned!

Trash 10-31-2017 11:21 PM


Originally Posted by Tractionless (Post 4591100)
Dorman (CTI) P/N-84598, TPS harness has corrected the 1100 rpm and blowing black smoke idle on the hose on cold startup.

I'll have the boat on the water this weekend with a scanner to see if it's still going to idle surge and die on the hose during flushout. Stay tuned!

So perhaps the lesson for all is to fiddle with the pins.....:D

Tractionless 11-07-2017 07:33 AM

As promised the on water update.

Fired and idled at the correct rpm and no surging on the ramp and in the slip prior to getting underway. No issues idling out of the canal nor when bringing the throttles up to 1k rpm on the way out. Two no wake zones taken at 1k rpm and no surging. I anchored for 3.5 hrs. And upon restart it idled high at 900 rpm but no surge when brought up to 1k rpm to no wake past the other boats at anchorage. Got on plane for 1/4 mile and back down to 1k rpm for no wake under the bridge and it was surging at the 1k rpm point. Had the wifey take the helm while I grabbed the scanning gear, I should have steered to the left and kept it surging as by the time were were back up on plane and to the next bridge a few miles away the (idle) surge stopped at the 1k rpm point. Back to the canal and to 1k rpm and no surging all the way to the ramp where it idled fine at the slip prior to loading. On the hose it idled like a champ and I didn't have to continually goose the throttle to keep the engine running for washout.

All in all it seems most of the issue is solved for now but I've been to this point before and prior to authoring the thread. I'll make a dedicated on water datalogging only day in the near future to assess all sensors etc in real time and try to poinpoint what seems to be an inconsistent situation within the engine electronic system.

Tractionless 01-06-2019 08:08 PM

I've been working on this for over the past year with scans etc. Upon the advice of another member today I pulled the vac. line to the fuel pressure regulator while the 1k rpm surging was taking place and it immediately stopped the surging. Even though fuel pressure reads good with the vac line attached at all times, including during surging I may be leaning toward replacing the FPR. I will update the thread with my findings.

Keith


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