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5.0l efi - Tach Jumping Wildly and Engine Running Rough Intermittantly

G

Goodtimes1

New member
Hello community - I am requesting a little help...

I have a 1998 Sea Ray 190 with the 5.0l efi and Alpha drive.. My problem started last fall, but since it was the end of the boating season I left it until this spring... What I have happening is the tach will start jumping around wildly.. Occasionally the engine will start running rough.. I found one of the spark plugs was fouled - replace them all (thought I probably had the problem fixed - nope).. I kept a close watch on the tach and what is happening is when the tach has a solid reading (any rpm) the engine runs fine.. When the tach starts jumping around, if the reading stays below about 5200 rpm the engine runs fine.. If the tach starts jumping above about 5200 rpm the engine starts running rough, when the tach reading drops blow 5200 then the engine starts running fine again.. I am guessing the ECM is seeing this same high rpm signal and rev-limiting the engine until the signal drops back down.. So I suspect the problem lies wherever the tach signal is generated.. I'm not sure, but I have heard the tach signal can come from the alternator or the ignition system.. I don't have any problem keeping the battery charged and the voltage is in the normal range.. The only other symptom I have seen was last fall, occasionally the engine would die when idling.. It would start right back up and if I bumped it into gear and gave a little throttle then it would not die.. I have not seen that this spring - the fouled plug may have been causing that issue..

I have checked wiring connections over the entire engine and under the dash and found nothing loose or corroded...

I don't see how it could be a tach problem - I don't think it would feed back to the engine and cause this type of intermittant problem.. I will probably disconnect the signal line to the tach for my next trip out and see if it makes any difference..

Any ideas would be appreciated... Thanks...
 
I don't see how it could be a tach problem - I don't think it would feed back to the engine and cause this type of intermittant problem.. I will probably disconnect the signal line to the tach for my next trip out and see if it makes any difference..
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Ayuh,.... Welcome Aboard,... That's what I'd do,... tachs go Bad too....
 
I will probably disconnect the signal line to the tach for my next trip out and see if it makes any difference...
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That is the first step in solving the problem. If the engine runs great you can remove the tach and clean the terminal connections w/light sandpaper. Because corrosion can build up inside of the switches, squirt a little WD-40 into each of them on the back of the tach and exercise them B-N-F and reconnect it. Note the switch positions before moving them. If it doesn't help then you are going to need a new tach.
 
Thanks for the responses -- I've already pulled the tach, cleaned the connections and exercised the selector switch on the back of the tach.. That did not help at all.. Looks like the plan is to go out tomorrow and I will disconnect the signal wire and see what happens....

Thanks again..
 
Goodtimes1 said:
Thanks for the responses -- I've already pulled the tach, cleaned the connections and exercised the selector switch on the back of the tach.. That did not help at all.. Looks like the plan is to go out tomorrow and I will disconnect the signal wire and see what happens....

Thanks again..
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You stated that the engine acts up at the same time the tach goes whackey when above 5200 RPM, is that correct? Have you had the ECM scanned for codes / problems, or scanned while at the highr RPM? If the 2 problems happen at the same time, seems as though the common denominator there would be the ECM / EFI circuitry, or possibly voltage / connection to the ECM / EFI modules. Do you have another tach to connect to see if the problem still exists above 5200 rpm with a different tach? It is possible for any component connected to the ECM / EFI circuits to breakdown under stress (high RPM) and induce a problem into the ECM/ EFI circuits at the same time.

Looking at some electrical diagrams, looks as thought your tach lead comes off the connection between the ECM and EFI circuitry, not the charging circuitry, which could point to the correlation of both going crazy at the same time. Just a thought.....


Most of my documentation is for 454 / 7.4 L / 502, but did find some refferences to the SBC EFI (TB and port injection) in some other docs I have..

Keep us posted.
 
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Find all connectors, pull them apart one at a time and inspect very closely.

The EFI systems are very suseptable to bad pin connections

Some terminal/pin grease added to each connector would or could be a good thing.

There have been a few posts here over the last couple of years with wierd things happening to EFI systems and several found bad connections.
 
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I have not had the ECM scanned, I live about 45 miles from the nearest shop that can scan it..

The engine starts running rough when the tach is wacking out and goes above a reading of about 5200 rpm -- the engine is not turning 5200.. I can be cruising at about 2800 rpm, the tach will start jumping around, the engine is fine until the reading on the tach goes above 5200 then the engine starts running rough, but then engines rpms don't increase listening to it.. I don't know for sure if there is any rev-limiter function in the ECM or not - that was a guess by me by how it was acting.. I don't have another tach - thinking about that - maybe I can find one to borrow for a test..

We are about to head out on the lake with the tach disconnected to see if that makes a difference.. If the problem still shows up then I will pull the connectors apart for the ECM and have a good look - I wiggled them and pushed on them already to make sure they were tight, but did not pull them apart...

Thanks for the thoughts and suggestions..
 
OK - update...

Went on the lake with the tach lead disconnected -- still have the rough running issue intermittantly... Next step is to check and clean the ECM connectors - then back out to test again hopefully tomorrow....

Thanks again everyone....
 
Goodtimes1 said:
OK - update...

Went on the lake with the tach lead disconnected -- still have the rough running issue intermittantly... Next step is to check and clean the ECM connectors - then back out to test again hopefully tomorrow....

Thanks again everyone....
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Grab a can of contact cleaner and spray the pins of each connector, dry them out and use some connector lube to keep the moisture out after they are back together. Sometimes, the troubleshooting of electrical problems (especially on ECM motors) can be very frustrating. One step at a time, test, try next possibility, test and repeat. Even an ever so slightly loose pin connection will look fine, but be crap if any moisture / dirt / slight corrosion gets in there and it's usually the hardest one to get to.
 
I have checked the connectors on the ECM, ICM, coil, knock sensor module, and any other connectors I ran across.. Every one looks shiny, no hint of dirt or corrosion.. I did hit every one with contact cleaner, but I don't have any connector lube here, will pick some up next trip to town.. I figure if it is a connector problem, maybe using the contact cleaner will at least correct the problem and I can add the lube later to seal the connections.. I did see in the service manual to check the ECM and motor grounds if there is intermittant problems - I am going to disconnect them, burnish them up and snug them back..

Very bad winds here for the next couple of days so no lake time till the water smooths out...
 
Here is my update.... (log-winded, sorry) I see people listing the engine SR# here is mine if it will help 0L025228

Still have the problem.. I got some anti-corrosion and lube for electronics (deoxit).. Cleaned the pins and connectors for the ecm, icm, knock sensor module, cable that goes to the console, and any other connector I found along the way.. Cleaned the ground connections on the engine and on the ground bus at the console..

I read the ecm codes with this procedure ---

>>>>>>>>>>
How to make a Marine EFI Code tool for under $1.00

Materials needed:

One 12volt resistor type LED light
One small paperclip cut in half

This home made code tool should work on all GM MEFI 1,2,3 or 4 marine EFI systems with the ten pin DLC (Data Link Connector).

How to hook it up:
1) Ignition key “OFF”
2) Remove the cap from the Data Link Connector (DLC)
3) Slide the LED into the female terminals of position E and F on the DLC, making sure that the positive side goes into terminal F and the negative side into terminal E
4) Turn the ignition key to the “ON” position (LED should come on)
5) Insert the half paperclip into terminals A and B – This puts the engine in “Service Mode” - (you will hear fuel pump come on, and code will begin to flash on the LED)
6) Read codes by observing LED flashs. If the self diagnostic system is working it will flash code 12 – one flash, pause, two flashes, long pause – it will repeat three times. If other codes are present they will flash in order of lowest to highest.

For more details on how to read codes, clear codes, what “Service Mode” is, how to set base timing, etc. refer to appropriate service manual.

I don’t recommend making and using this tool unless you are confident that you can do it correctly. Hooking it up incorrectly could damage the ECM."""
>>>>>>>>>>

What read out was 12,12,12,43,43,43 (then repeated)..
43 is for the knock sensor code..

I tried to reset the codes with this procedure ---

>>>>>>>>>>
Clearing Codes Using CodeMate Tester
NOTE: When clearing codes without the use of a scan tool, the battery must be fully
charged. The ability to clear codes is directly dependent on the battery being fully charged
and able to start the engine with adequate cranking rpm.
1. Install diagnostic CodeMate Tester.
2. Turn key ON.
3. Select “Service Mode” on CodeMate Tester.
4. To clear codes, move the throttle, while in NEUTRAL, from 0% to 100% then back to 0%.
5. Exit “Service Mode” on CodeMate Tester.
6. Start engine and let run for fifteen seconds.
7. Turn key OFF for 5 seconds.
8. Select “Service Mode” on CodeMate Tester.
9. Turn key ON and read codes. If codes are still present, check preceding “Note” and
repeat from Step 1.
10. Refer to appropriate Troubleshooting and/or Diagnostic Charts.
A poorly charged battery or engine cranking problem may result in an ECM “reset” and may
not allow stored trouble codes to be cleared from EEPROM memory. If this condition exists,
BE SURE the battery is fully charged.
NOTE: If a low battery condition does exists the audio warning buzzer will come on for 2
seconds (as a result of an ECM reset) after engine start-up."""
>>>>>>>>>

I was unable to reset the codes.. I thought just using the paperclip jumper going in and out of service mode would be the same as the codemate tester.. Maybe not - but the codes would not clear..

Out to the lake for a test run.... Problem is still there.. Two things I did notice - as I increased the rpms at about 3500 rpm the tach would start the wild jumping and the engine would miss.. If I kept increasing throttle the engine would start running normal again with the tach reading about 4200 rpm and I could increase up to max throttle with no problems.. Slowing down was the same, at about 4200 rpm the tach would start jumping, the engine would miss, but as I slowed, the tach would settle about 3500 rpm and the engine would run normal again.. I even tried another tach this trip and there was no difference.. The second thing I noticed was when the engine was cool, little or no problems.. The longer I ran the engine the more pronounced the problem became.. It got to the point where the engine even backfired a couple of times.. Now I wonder about a heat related problem..

While I was out I disconnected the knock sensor on the engine block - no difference.. Then I disconnected the knock sensor module - no difference..

Back off of the lake I read the codes again - 12,12,12,43,43,43 repeat... I don't know if these codes are old codes or new since I can't reset them.. But, should I be seeing more of the 43 codes if that is the problem?? Or, does the ecm only hold the last three codes??? I guess it is possible these are old codes and there are not any new codes being thrown..

Unless anyone out there can give me any more ideas - it looks like I will have to purchase a scantool to read live information when the engine is acting up, or take it to a shop that can do it..

One question I have, if I buy the scantool, hook it to read the engine live when it is missing - isn't there a possiblilty several of the sensors will be showing not normal since the engine is missing and backfiring????

Any thoughts from the great minds out there ????
 
You found a knock sensor code but disconnectiong it did not change anything? Is it buried under the intake manifold? Wire may be corroded.
 
The knock sensor is on the right side of the block, down by the drain plug.. The wire is good following it back up to the harness and then the harness is in good shape everywhere on top of the engine.. Even if the wire to the knock sensor was corroded, when I disconnected the knock sensor module, which sits by the ecm, that would have eliminated the wire as a source of problem.. That is right, with the knock sensor and the knock sensor module disconnected it made no difference - the problem is still there..

Any other thoughts ??
 
From the schematic it looks as if there is one wire going to the knock sensor, Correct?

If this is true then how does the sensor function? See below for the knock sensor and knock module info.
 
Thanks for the info in your attachments.. Something to dig deeper into, but just a gut feeling to problem is not with the knock sensor.. I can see how I would have set a code 43 when I disconnected the knock sensor module and the ecm didn't see the 10 volt signal for an extended time.. But how the original 43 was set is a mystery.. From everything I read it looks like the knock sensor signal is either on or off (the 10 volt signal). I can see this causing the problem if the signal is turning on and off and causing the engine timing to change, but if the knock sensor module is disconnected this signal will be constant, not changing, and the engine shouldn't miss and run rough..

You are correct - one wire going to the sensor.. How does it work - my guess - there is a solid state sensor inside that vibrates when it feels the shock of an engine knock.. The electrical path is using the engine block as ground and on the sensing wire the resistance changes with the vibrations.. I would think there is a threshold level in the sensor so any small vibration in the engine or boat would not cause an output change..

Thanks for the help...
 
I have been gone for a while, but finally back to boating. I need to update this old thread to possibly help others...

The final solution to my problem -- replaced the shift interrupt switch.. All the problems are gone - engine is running great and the tach is steady as a rock from idle through full throttle. The old switch checked good with a meter, but I am guessing the contacts were flaky from the vibration at certain rpm's. I happened to stumble across a youtube video about a jumping tach and they replaced this switch..

I was told by many people this switch would not solve my problem, guess they were wrong.

I have found many discussions where the final solution is never posted, so I thought I needed to close this issue with the solution. Hope this helps someone with their problem.
 
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