Intermittent engine alarm with RPM blip

[Moonstruck]

Engine: 1998 Mercruiser MCM 5.7L EFI (gen 1) TBI fuel injection serial # OL 089037

Drive: Mercruiser Bravo 3 serial # OL 188880 transom mount # OL 284722

Problem: Intermittent engine alarm accompanied with a jump in RPM to about 1000, dropping off to 800 until the alarm shuts off, then return to idle RPM. In a test run starting from a cold engine, run time of 9 minutes alarm sounded 14 times.

What has been done: The drive oil switch, oil pressure switch, and ECT have been disconnected for tests and the alarm still sounds with these switches disconnected. A stuck t-stat was suspected, so that was changed out. The old t-stat tested OK. A piece of raw water impeller blade was found in the t-stat housing on the cold side of the t-stat. Inspection of the raw water pump showed no missing pieces. Also, no missing pieces from last impeller change out. Circ pump was pulled and block was drained and back flushed until clean. Put it all back together, cooling system appears to be functioning to warm up as observed with IR thermometer. Oil pressure sender shows 39 psi at idle. Drive oil float can be moved freely down & float up with sounding of alarm when down and ending when float rises. Engine scanned for codes, no codes stored. Alarm sounded when scanner was attached and was noted as IAC running 95%. Mechanic wants to do a fuel pressure test next. I am currently waiting on results. Except for the alarm, the engine appears to be running normally. I do not know why the alarm is sounding, and I do not want to damage anything.

History: This engine has had a series of run rich problems over the years. Last winter the TBI was rebuilt with new injectors, TPS, IAC. This still did not solve the problem. Then the ECT was changed out and all problems disappeared. Engine ran great all last season.

Thank you.

 

[Fun Times]

Hi there, welcome to iboats! Please know that on some EFI engine models that if you unplug a sensor you may hear/set off the warning horn and set a code that should have been seen once the scan tool was read correctly. Some of these TBI engines have a fuel pressure sensor while others do not. Your engine model was about right when they were starting to installing them. So it's a 50/50 if you have one or not. Your serial number does not show you to have one but I have seen that to be false information in the past regarding the fuel sensor. If you do have one, it should be located on the throttle body. Fuel pressure is a good idea to check even if you don't have a sensor. Keep track of the numbers so you have a reference to go off of in the future if needed.

He could try cleaning the IAC to see if he can get the IAC counts down closer to 25- 40 counts like more normal. Make sure the numbers are moving. He should see a code if the warning horn is sounding. Especially if he cleared them and the horn is still sounding. Has he checked ignition timing to see what it's at and to see if it will stabilize while locked in base timing mode? You may have a toggling problem with the module located under the distributor cap. Also remind him to keep an eye out for general warning one or two. They will not set a code but will sound the warning horn and you can only read it on the scan tool while it's happening. Reading the live data may help give an indication of what should be out of the ordinary. Low voltage will make the engine run like this while sounding the horn. Check all power and ground cables and wiring for loose, corroded, backing out pin connections...including the sensor plugs. Let us know what he finds, good luck.

 

[Moonstruck]

Thank you for the welcome. When the sensors were unplugged, the engine was always off. Alarm sounded with and with out sensors connected. Unplugging a sensor did not trigger an alarm during the last test run. No codes at all reported in the scan last week. Is it possible for the code storage to be malfunctioning? End of 2009 season it had a code for MAP sensor. The sensor was replaced, code cleared, no improvement in engine performance. Since then there has never been a single code stored. No fuel pressure sensor on this engine. The IAC was replaced spring 2013. Is it possible to go bad in a year? I can pull that easily enough to check for dirt. Please educate me on the IAC counts. As the number goes up, the IAC is open more, therefore letting in more air, correct? The 95% was only when the slarm sounded. I will have to ask what the counts were when the alarm was not sounding. What would be normal spec for the counts? Timing was checked fall 2012. Need the scan tool to put into base mode, I'll have them check. What is a toggling problem, and to which module do you refer to? I do not know what you mean. What is general warning one and two (warning of what)? In spring 2013 I disconnected, cleaned, and greased all the ground cables, ground blocks & bus bars, and wires on the bus bars. I did the same for the hot side. Also I checked the ECM harness to all the sensors for continuity to the sensor one sensor at a time. I did all the tests listed in my repair manual that did not require the scan tool. All check out. I had a voltage meter on the battery when I ran the last test. Rock solid voltage before, during and after the alarm. I think I should try to read the voltage at the ECM feed. Hopefully they have done the pressure test today. I will head to the boat tomorrow. Thanks for the help. I will keep informed.

 

[Moonstruck]

I think the computer burped...

 

[Moonstruck]

Here is an update- there is no signifigant progress. After two weeks, all the mechanic has been able to accomplish is plugging in a scanner and tell me that there were no codes, the ECM says all is well, with the exception of IAC running at 95% when the alarm sounded. The person at the service desk did say percent, and I asked if that was a percent of total possible counts, or was that counts he meant by percent. He said that was a percent of total possible counts. I asked him w\hat the total possible counts was, and he said that he did not know, would have to ask the mechanic. I asked what it was running at when the alarm was not sounding, and he said he did not know. I believe I read some wher that 220 was the max, which would be 209 counts (way high), but I could be mistaken about the 220 number.

I removed the IAC with the intent of cleaning it. It was clean as a whistle. There was nothing to clean off. Nothing in the TB either. I have a small remote camera on a flexable casing for looking into small things. I used it to look in the hole where the IAC came out of and that was clean also. I reinstalled the IAC, and just because, I cleaned every terminal connection at the fuel injectors, IAC, TPS, MAP, ECT. Also took a voltage reading off the data link connector instead of right off the battery. With the engine running, I had 13.94 volts at the datalink connector vs 14.30 directly off the battery and 13.1 volts on the engine battery before start up, but after shutting off the battery charger. The alarm sounded 4 and 4.5 minutes after cold engine start up. When the alarm sounded, the voltage never dropped below 13.93 volts. Maybe it took 0.01 volts to run the alarm horn? There was the same jump in RPM to about 1000 when the alarm sounded, then drop and hold at 800 until the alarm shut off then back to idle. As odd as it may sound, it acts like the alarm is causing the RPM jump.

So I saw no problems with the IAC as far as the hardware goes, something must still be kicking it for the RMP to jump. I still need to check the fuel pressure. Can someone please tell me where to tap in to check that? There is a plug in the TB that was the fuel return when the TB was used in automotive applications. Now it just plugs the hole. Can I remove that plug and tap in there to test fuel pressure, or should I rig up a "T" fitting on the existing fuel line connection at the TB, or somewhere else?

 

[thumpar]

I have read that there are some codes that will not get stored and you have to have the computer hooked up while it happens to know what the error is.

 

[Moonstruck]

It appears that I may be at a wall in diagnostic with out a scanner. Seeing that the marina said that it may still be weeks before they can look at it, I was considering this product (see link). Does anyone have experience with this? Is there something else that I should use?

http://www.aldlcable.com/mefiscan.asp

 

[alldodge]

It appears that I may be at a wall in diagnostic with out a scanner. Seeing that the marina said that it may still be weeks before they can look at it, I was considering this product (see link). Does anyone have experience with this? Is there something else that I should use?

http://www.aldlcable.com/mefiscan.asp

I would suggest the Rinda scanner
http://www.rinda.com/marine/marine.htm

 

[alldodge]

Here is an update- there is no signifigant progress. After two weeks, all the mechanic has been able to accomplish is plugging in a scanner and tell me that there were no codes, the ECM says all is well, with the exception of IAC running at 95% when the alarm sounded. The person at the service desk did say percent, and I asked if that was a percent of total possible counts, or was that counts he meant by percent. He said that was a percent of total possible counts. I asked him w\hat the total possible counts was, and he said that he did not know, would have to ask the mechanic. I asked what it was running at when the alarm was not sounding, and he said he did not know. I believe I read some wher that 220 was the max, which would be 209 counts (way high), but I could be mistaken about the 220 number.

I removed the IAC with the intent of cleaning it. It was clean as a whistle. There was nothing to clean off. Nothing in the TB either. I have a small remote camera on a flexable casing for looking into small things. I used it to look in the hole where the IAC came out of and that was clean also. I reinstalled the IAC, and just because, I cleaned every terminal connection at the fuel injectors, IAC, TPS, MAP, ECT. Also took a voltage reading off the data link connector instead of right off the battery. With the engine running, I had 13.94 volts at the datalink connector vs 14.30 directly off the battery and 13.1 volts on the engine battery before start up, but after shutting off the battery charger. The alarm sounded 4 and 4.5 minutes after cold engine start up. When the alarm sounded, the voltage never dropped below 13.93 volts. Maybe it took 0.01 volts to run the alarm horn? There was the same jump in RPM to about 1000 when the alarm sounded, then drop and hold at 800 until the alarm shut off then back to idle. As odd as it may sound, it acts like the alarm is causing the RPM jump.

So I saw no problems with the IAC as far as the hardware goes, something must still be kicking it for the RMP to jump. I still need to check the fuel pressure. Can someone please tell me where to tap in to check that? There is a plug in the TB that was the fuel return when the TB was used in automotive applications. Now it just plugs the hole. Can I remove that plug and tap in there to test fuel pressure, or should I rig up a "T" fitting on the existing fuel line connection at the TB, or somewhere else?

The reading you should get is counts not percentage as Fun Times mentioned. Manual states it should be between 0 to 40 counts and idling would normally get you around 25. Throttle position .4 to .8 volts, IAc follower 0 counts, MAP 1 to 3 volts. Wonder if you mechanic has the correct version of software installed in there scan tool?

 

[Moonstruck]

AllDodge- Were you referring to the Diacom marine PC software, or suggesting I go with the Mercruiser scan tool? If I read the description correctly, the Mercruiser scan tool does not record data for later review.

As far as if the mechanic has the correct software version, I do not know. I do have concerns about their ability. Who would diagnose a rough running engine and decide a new distributor is in order when the engine has not been tuned for 12 years, and has the original ignition wires (date coded) and spark plugs in it (black engine paint over spray on plugs) with some of the gaps worn out to 0.052?

 

[Fun Times]

I still need to check the fuel pressure. Can someone please tell me where to tap in to check that? or should I rig up a "T" fitting on the existing fuel line connection at the TB, or somewhere else?

To check fuel pressure you would need to use Mercruiser part number 91-806901 installed between the throttle body "inlet fuel line" and the throttle body "unit" like see in here. http://forums.iboats.com/forum/engi...ting-to-measure-fuel-pressure-on-tbi?t=352594

As odd as it may sound, it acts like the alarm is causing the RPM jump.

Though it's very rare, it has happen in the past. You may have to send your ECM out for additional testing to the guy in your link above about the scan info you're interested about buying. This next link is not your engine, but just to show as an example that it has happened. See the second half: http://www.boatfix.com/merc/Bullet/93/93_02.pdf


I don't have any experience with the scan info in your link. But if you already have a laptop computer, then it looks like it will work to read some basic engine parameters. Not sure if you can clear codes with it though. Sometimes you need to clear them to see if they come back. The Rinda handheld scan tool is easy and very convenient to use and will do most everything you need. If you find a reason to need to record the data for later review, then the Rinda Diacom marine PC software or the link above should be the one to get. Back in the day before the Diacom software, we used to just write down the live data on a sheet of paper. Oh how times have changed, lol.

 

[Moonstruck]

Thanks FT. I will work on getting the proper adapter for the fuel pressure test. Very interesting on the ECM that was bad on that other engine. It looks like this was a factory error, therefore the recall. Does the ECM ever just go bad after 14 years?

 

[Moonstruck]

Just an update to keep the thread fresh. Three weeks now and the marina has done nothing for me but plug in their scanner, tell me there are no fault codes, and they sent me a bill! Good luck with that. Anyway, I have ordered a scan tool from Rinda, and a T fitting to check fuel pressure. I have downloaded the Mercruiser service manual, and will be starting top to bottom diagnostics. I plan to follow the manual and the scan tool flow chart to flush out the problem. If anyone has any diagnostic tips to offer they would be very welcome. I'm waiting on UPS for delivery, then I am off to the slip to tear into it.

 

[Fun Times]

Hanging back in the shadows till you do your testing. Let us know what you come up with, good luck.

 

[Moonstruck]

Here is an update. I received my scanner from Rinda. They have a new one now called Techmate Pro. A big thank you to Ed at Rinda for helping me understand the wild readouts from the scanner (see youtube link).

It turned out to be a combination of a bad IAC motor, and a distributor cap (new) that had an arch cut through the insulating collar surrounding the center button. My theory is that the errant spark did not go where it was supposed to go, the ECM detected no spark, shutting down the injectors, then inertia keeping the engine going, spark return, RPM down, kick the IAC, MAP sees pressure rise, ECM senses rise, dumps fuel, goes way rich, RMP drops. I believe this lead to a toggling situation. I believe that the toggling caused the ECM to reset (maybe that is the cause for the alarm beep). If you watch the vid, you can see the screen go blank and say resyncing... Also in the vid you can see that the rngine test run time in minutes, (not total engine time) keeps resetting to 0. Ed explained that each time this happens, it means the scanner lost signal to the ECM because the ECM had reset itself. This type of reset is often caused by a power drop to the ECM. This drop can last only milliseconds, so you will not see it on a volt meeter or scanner. So I was chasing a cause of a power drop. Apparently the errant spark triggered a series of events that caused the power drop, and resetting the ECM. Once the distributor cap was replaced with last year's old one, cleaned up, the problem disappeared, and there was no resetting of the scanner or clearing of the run time minutes indicating errors. The rest of the parameters fell into place and the engine ran great. Why this caused the alarm to sound I still do not know, it is not in the schematics of the engine. Must be something in the MEFI-1 program. I never did get to the fuel pressure test. Since the I put the engine through it's paces this afternoon and it performed well I think I will just enjoy the boat for the rest of the season.

Thank you everyone for your help and suggestions.


https://www.youtube.com/watch?v=JRD6rMPYYLg

 

[Moonstruck]

BTW did anyone notice the spark advance reading of -1,415.5 degrees? As impossible as it sounds, in a way that is really what happened :lol: