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Thunderbolt V ICM 1997 5.7L

troym

troym

Advanced Contributor
1997 5.7L, 2bbl mercarb, TB V (w/o knock sensor), Alpha I Gen II.
Seems I've been chasing my tail alot with following symptoms, all of which have been intermittent, in no particular order, no appart cause during recurrance and follow-on disapearance of the symptom(s): lack of power, rough idle, poor fuel economy, and stalling shortly after restarts when engine is warm.

What I've done so far:
- checked all ignition wiring for shorts, grounds, bad terminal connections, etc. ...no smoking guns.
- new dist cap and rotor. Old ones weren't what I'd consider bad, but cheap and easy enough to replace.
- new plugs and wires. Old ones same as above.
- replaced carb needle and seat, replaced power valve, verified correct float level and drop, cleaned carb. Checked float weight (9 grams). Once again, no smoking guns.
- replaced fuel/water separator and fuel filter on carb. No smoking guns.
- fresh fuel, added stabilizer. No reason to suspect bad gas, used the boat enough this summer to keep the gas pretty fresh, unless I got some bad gas from the gas dock.
- checked & cleaned fuel tank vent cap screen. No smoking gun.
- checked fuel pressure.. 7psi. (mechanical pump) No smoking gun.
- checked choke setting and operation... 2 marks to open, opens about a minute after energized. No smoking gun.
- Set idle speed and mixture per the manual. (ICM in base timing mode, etc). No noticeable improvement, but at least eliminted this a possible cause for one of the symptoms.

After the last round of troubleshooting and eliminating possible problems (Sunday), I took the boat out for a test run. Had no reccurance of the stalling after restarting this time, but the engine had a noticable miss at idle, and it lacked power terribly. It seemed to accelerate OK up to about 3000rpm, but the miss got more noticable, and it really struggled to get the boat on plane.

Could this be the beggining of the end for my ICM?
I would think if it were bad, it would just stop working all together (i.e., no spark)
The troubleshooting chart for the ICM in the Merc manual doesn't help much... I have spark, the engine runs, it just doesn't run right.
 
Re: Thunderbolt V ICM

Remove and inspect the spark plugs checking to see if any show a "pure white look" verses the others suggesting water intrusion.
Have you checked the fuel line and check/inspect the anti-syphon valve at the tank?
Try removing the main fuel line at the engine filter and hook up a remote tank for testing.
 
Re: Thunderbolt V ICM

Had a water intrusion issue last year... new manifolds, spacers and elbows. The water that got in the engine was engine coolant, not raw water.
Changed the oil about 6 times, and up until a couple weeks ago, the engine ran great since.
Was thinking a compression test would be in order, will do it this weekend. I'll read up on the vaccum test and see if that's within my capability too. I'll take a look at the plugs while they're out too. Now that the engine has run with those plugs, there may be something noteworthy.
More to follow next week.
 
Re: Thunderbolt V ICM

Vaccum test looks pretty straight forward. Pretty sure I have a gage somewhere too.
Any suggestions on where to hook it up? Pretty sure the carb doesn't have any connection points. Don't remember seeing any plugged holes in the manifold, but I never realy looked for any.
 
Re: Thunderbolt V ICM

Troy, I read that you have tested, checked, and eliminated most all components. Unless I missed it, I see no mention of testing and/or trying another module.

Your ignition is M/C's version of EST (electronic spark timing).
The ICM controls your spark lead on this type of ignition.
It is triggered via a photo eye sensor.
I believe that it actually delays spark, since it would appear that we can't make things occur before they actually occur.
So, this is all done via the electronics and algorithm of the programmed ICM.

Your knock sensor tells the ICM to cut back on TA if knocking or Detonation should occur.
This can become a cat'n mouse game if the ICM is failing, **or if the ICM is receiving bad data from the triggering device.

Maybe it's time to consider this module!

Another possibility:
Like said, your ignition uses photo eye sensing or triggering.
The openings in the special rotor unit turn the photo beam on/off!
I don't claim to know this TB system very well, but I seem to recall that some rotor units are epoxed, or somehow glued into position (I may be wrong on this).
The oil pump load on the "non-advancing" type distributor, should check any slack!
However, if your rotor has become loose on the distributor shaft, this may cause an erratic spark issue, or **Bad triggering data being sent to the ICM.


Again, I don't know this system all that well......., but this may be some Food for Thought!

.
 
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Re: Thunderbolt V ICM

...your ignition uses photo eye sensing or triggering.
Click to expand...

What did your device look like when you removed the rotor? If you have the old style that can rust it may be contributing to your problem. There are tiny bare wires that corrode causing improper spark. I may have missed it but did you try another coil? If you find a loose plug wire it will reduce max. RPMs.

Vacuum source: look on the backside of the manifold at the carb riser for a plug. Remove it and install a nipple.
 
Re: Thunderbolt V ICM

Rick

He states in his post

NO spark knock controll,
The rotor if a Merc part not aftermarket is The start wheel is SCREWED to the rotor. No adhesive used for merc....
 
Re: Thunderbolt V ICM

No knock control model on this one.
I did not try another ICM... that'd be $400 test, unless someone is willing to let me borrow thiers?
Rotor is tight on the dist shaft, and sensor wheel is held to the bottom of the rotor with screws. The new rotor/sensor wheel assembly fit very snugly, no loose play. Did not use locktite... figured I might want to be able to get it off again someday.
Did not try a new coil, this one is pretty new, maybe 3 years old. Have spark, so didn't really suspect it. Can swap it out with another easy enough and see what happens. I'd love it if that was the problem.
Didn't see anything on the optical sensor that would indicate a problem, but I didn't look all that close. Will check that out too.
I also saw the following in the manual: "IMPORTANT: Proper positioning in spark plug wire supports is important to prevent crossfiring." ...hooda thunkit?

What I plan to do:
1. Remove the dist cap and rotor and take a better look at the optical sensor.
2. Remove the ICM and take a look for evidence of any water getting into it.
3. Reinstall above and swap out the ign coil, and check the routing of the plug wires.
4. Start the engine and let it warm up.
5. Perform vaccum test.
6. Pull the plugs, inspect them, and perform compression test.

Will post data and results. Won't get to it until Friday or Saturday though. Any additional thoughts or suggestions are more than welocome!
 
Re: Thunderbolt V ICM

Good plan. But there are other ways then a icm module that costs 400 bucks.

The first site i posted mentions where to look for a place to hook the gauge.

Lets see what the vacuum test reveals.

Little used now as a trouble shooting tool the vacuum test, some have a gauge hooked right at the helm.
 
Re: Thunderbolt V ICM

kghost said:
Rick
He states in his post NO spark knock controll,
The rotor if a Merc part not aftermarket is The start wheel is SCREWED to the rotor. No adhesive used for merc....
Click to expand...
Understood.... no knock sensor. However, this still does not eliminate the ICM as the source of the issue.

Not sure where I read about the rotor unit being epoxy (or ????) attached. Sounds like I'm mistaken on that!
 
Re: Thunderbolt V ICM

Back to the basics. For sure you have a clean fuel stream ?

No gunk on the bottom of your tank for sure ?

All filters for sure clean, the fuel pickup screen clean ?

The anti-syphon valve clean ?

The vent clear ?

You have good connections at the battery clean ? Good cables for sure ?

And the main ground at the block, removed and cleaned.

Ok NEW the ignition system you have was the best there was.

But thats the keyword " new ". When you have checked everything went thru everything, and you still can't figure it out, it may be time for a change.

Me i have been where you are now, went a different way, think about it, a new icm is 400 and may not solve your problem.
 
Re: Thunderbolt V ICM

One more thing to DOUBLE CHECK!!!!!!!!!!!!!!!!!!!!

SPARK PLUG WIRING!!

SEEN it f'up even by the most savy...............

just sayin.......
 
Re: Thunderbolt V ICM

Here's the data: Tried to post last night, but had to get my password reset. (This isn't the computer I usually use.)
- Optical sensor was a little dirty, cleaned it up... I believe it'll serve.
- No indication of water leaking into the ICM. Bone dry, clean as a whistle. Terminal connections were fine.
- Double checked spark plug wire routing and made sure the wires were connected to the right plugs... no issues.
- Warmed the engine to NOT (180F). Ran rough, but no stalling.
- Vacuum test:
- 15"Hg at idle, fluctuating about 1"Hg both ways. (didn't like this... seems low and the fluctuation seemed a bit drastic)
- On acceleration, vacuum dropped to 12"Hg then climbed to 20"Hg. (Low, but did what I'd expect)
- At 3000rpm, vacuum steady at 20"Hg.
- On decelleration, vacuum increased to 22"Hg, then dropped back to 15"Hg while at idle, fluctuating again.

- Compession test:
#1- 0psi (zero!) #2-175psi
#3- 140psi #4-165psi
#5- 170psi #6-165psi
#7- 170psi #8-170psi

Ok, so low vacuum and no compression on #1... all things considered, it runs pretty good for a 7 cylinder!
Also, there was some carbon deposits on #3's plug. That along with lower compression, compared to the other cylinders that have good compression, indicates something going on in there too.

Next step: Haul the boat, get it closer to the tool box and start by pulling, at a minimum, the port side cylinder head. See what broke. If it's the head gasket, I'll consider not pulling the other head, anything else... well there's my winter project!
 
Re: Thunderbolt V ICM

woa you have to yank the covers anyway, look see maybe a tuliped valve, stuck valve. Broke spring ?

What cylinder you have water in before ?

I think this is a continuation of your water intrusion problem was not handled properly.

Hence these problems.

You boat in saltwater?
 
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Re: Thunderbolt V ICM

Zero compression on number one and lower on number three could very well be a head gasket, Zero on one though would seem to be a bad valve train component (valve stuck open). A bad head gasket I would think would just register low NOT ZERO.......

Pull your valve cover and carefully inspect #1 and #3 rocker arms and all first......May still require head removal but ONE STEP AT A TIME!!

Also look close for evidence of water........and valve stem deposits,,
 
Re: Thunderbolt V ICM

The water in the cylinders was on that side of the engine, but I don't think it was limited to any one particular cylinder.
When I finally realized what was going on... the loss of coolant finally became noticable, I already fried 2 staters, bent a set of starter mounting bolts and ripped a dozen or more teeth off the flywheel trying to compress water.
So it's not so much an issue of how it was handled once I figured out what was going on, rather that it took so damn long to find the real problem, all the while causing whatever damage I've yet to fully discover. So I could kick myslef for not putting two and two together WRT hard starting and loss of coolant, that is a hard lesson learned. But looking back at what I've done since finding the water in the cylinders, I don't think I'd have done anything differently. At the time the engine was running as good as it ever did, and contuinued to do so up until a couple weeks ago. Comparing what work I would have had to do to prevent what I'm having to deal with now, I don't think would have been significantly less then what I'm going to have to do anyway.
So I got the summer out of it... now it's time to pay the piper. Just wish it would have held together long enough to catch a few stripers.
I'll let y'all know what I find when I start tearing into it, hopefully Friday. I, sure as hell, am not going shopping!
Thanks for the support.
 
Re: Thunderbolt V ICM

Not at all, chiefalen. I appreciate your time and honesty. I didn't mean to sound defensive, just sharing my thoughts.
 
Tore into this afternoon.
Didn't see anything wrong with just the rocker arm cover off (Pic #1), continued deeper and pulled the cylinder head off.
Found the cause for zero compressin on #1... bent exhaust valve. (Pic #2)
There is also evidence of the exhasut valve making contact with the top of the piston (Pic #3)
Also took a picture (#4) of the exhaust valve next to a straight edge...yikes!

#1.jpg#2.jpg#3.jpg#4.jpg

So what would cause the valve to come in contact with the piston? Weak spring? Incorrect adjustment?
 
Everything you listed could be the cause.

I have found that people just don't set up the valves right maybe it's just me.

Most times they are to tight.

Maybe valve got sucked in, one revolution would be enough to bend it.

Pushrods bent also ?

How about the connecting rod on that one piston it twisted ?

Wrist pin, every piece look them over just make sure you mark exactly how it comes off.

Me i hit it with a dimple both sides.
 
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Pushrods are straight.
I've only taken the #1 cylinder valves out so far, both the springs' free height are low. Exhaust: 1.935", Intake:1.975". Spec per my book is 2.030".... 0.095" enough to call the spring tired and worn out?
My plan now is to pull the other head, replace the bent valve and lap it in, clean up all the other valves and seats. Blue check them, and lap as necessary. Nothing I've seen so far indicates any reason to have any seats cut... that may change as I get things taken apart.
On reassembly, I'll replace all the springs and stem seals. That should do it for the heads.
I want to pull the lifters out and take a look at those. Don't expect to find anything, but you never know.
I also want to pull the oil pan off and take a good hard look at the bottom end. I think at least #1 piston is worth pulling out adn replacing, and I'll take a good hard look at the conecting rod, and wrist pin.
While I'm at it, I'll replace the timing gear cover so I'll have timing marks again (see a previous post of mine... the little tab is gone from mine, currently).

Doesn't look good for striper season this year.

I think I'll atart another thread when I have any new info. The title of this one is a little misleading. Pretty amazing what I thought could have been an ignition problem led to this.
 
This may be just a me thing, but from what you are describing it would tend to make me want to simply replace the engine. A rebuilt long block is only about 1600 and while the urge to tinker and do it myself is very strong, I have at long last learned that it is often best to simply cut one's losses, admit defeat and move forward. A rebuilt engine will have a warranty and is simply a bolt in and go proposition.
While I was at it, I would splurge on a 4 barrel intake manifold, a Edelbrock 1409 carb, Comp Cams Extreme Marine cam,a MSD diz and be done. Oh and paint everything with POR-15 engine enamel.
 
Keeping all my options open, but for the momment not really interested in a new or rebuilt engine.
I think this one is worth saving. Haven't researched all the parts just yet, but I think I'll end up spending less than $500.
 
Not saying it's not worth saving, or that you aren't capable, but what you describe will cost you way more than 1600 in your own personal time and effort. You have to charge yourself $90 per hour shop time in your calculations; your time is not free. Plus, with the gaskets and small parts, and the fact that you are reinstalling an engine with a known catastrophic failure...
Do you really want to head out against the sea with that?
 
So, assuming it would take me 20 hours to do the work, and my time is worth $90, I could save $1800 by not doing the work... and since a new engine is $1600, I wouild acually be $200 ahead, what a deal! I'll stop what I'm doing right now. Please send my new engine and $200 soonest.
Seriously, thanks for the input, not the best time to be spending a ton of money... $500 vs. $1600+ ...going have to go with the $500 and deposit the sweat equity into the quagmire of thankless effort. If I get a few more years out of it great, if not we'll shovel that snow when it falls. All I can do is the best with what I've got.

WRT to ignition timing... never adjusted it since I owned it. When I went to check it recently, that's when I discovered the timing tab gone. No indication that the tab was ever there. Not sure how the mechanic installing the reman short block (bfore I bought the boat) ever set the timing... probably winged it. So that is on the short list of probable causes.
 
troym said:
Not sure how the mechanic installing the reman short block (bfore I bought the boat) ever set the timing... probably winged it. So that is on the short list of probable causes.
Click to expand...

Here's a likely scenario:
Engine at 0 degrees TDC on compression stroke. Install distributor with rotor pointing at #1 spark plug wire location. Start engine and adjust distributor 5 degrees or so + or -. Probably done by ear/feel/educated guesstimation of where timing mark is on standard issue Chevy 350. In any case within range where it would run OK.
 
You can buy an aftermarket timing marker that bolts on using existing timing chain cover bolts, I did at Auto zone I think, maybe it was NAPA. It worked like a charm.
 
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