Tachometer bouncing at 2,200 RPM

[fentong]

I just bought a 2001 Maristar 230VRS and it has a problem with the tach bouncing upwards (spikes) between 2,200 and 3,000 RPM. I had it taken into a MC dealer in GA today and they tested a new tach and it does the same thing. They thought that if the box under the dash was bad then probably other gauges would malfunction as well. The Distributor pickup is another option but they thought that would also affect the ignition (which is perfectly fine) so they are discounting that. The previous owner said that this happended once before under warranty and they replaced a 'distributor module' which fixed the problem.

Any insight or tests I can run to narrow this down?

[fentong]

No takers? Can anyone recommend a test or structured analysis to isolate the cause? I was going to go ahead and try to replace the pickup in the distributor but I'm a little concerned about the jumper for setting the timing as the distributor needs to come out.

[oldriver]

could be a grounding issue,Does the boat have perfectpass?That could be an issue if it is tied to the tach.

[JimN]

Does it happen at rest or just when you're under way? If it happens more often when you hit waves/wake, it would seem that something is loose. Make sure the grounds at the rear of the motor are clean and tight.

Sounds like this has TBI, so one place to look is at the base of the distributor, and if it's dirty and/or corroded where it attaches to the block, the bad ground will often cause this. Remove the hold-down clamp and clean it, along with anything it touches. Once these are clean, re-install the clamp and try it.

Before you change any parts, remove the screws from the ignition control module in the distributor and make sure there's no corrosion. Also, make sure any harness plugs are snug and the terminals are clean. Look for any terminals that look like the clip don't make good contact with the pin they connect to.

"but I'm a little concerned about the jumper for setting the timing as the distributor needs to come out."

Care to explain this? The only jumper needed for setting the timing would be at the DLC (Data Link Connector) at the rear of the motor (black plastic with gray wire retainer).

[bigmac]

My observation here on Team Talk over the last several years is that about 90% of the electrical problems are related to bad grounding.

[JimN]

"My observation here on Team Talk over the last several years is that about 90% of the electrical problems are related to bad grounding"

It's not just here. This is true of all electronics.

[fentong]

Thanks for your input it seems that I have a few things to try this weekend.

No perfect pass on this boat "yet"!!!
Yes it is a TBI 310 HP.
I'm really not sure if this bounces if I rev the engine in Neutral while the boat is at rest.


My comment about the jumper cable was in reference setting the timing. I was intending on pulling the distributor to replace the pickup module. I read on some posts here that I need to jump some electrical connector to put the engine in Set Timing Mode. I have an induction timing light and have set the timing on many cars but I'm not familiar with the "jumper" requirement on this Indmar and where I would find the connector to jump. YOu desribed the connector in your post JimN and I understand it's the first and second connectors (from left) I jump. The INDMAR service manual for my engine that there are "special tools" required to set the timing.

When you say to loosen off the base of the distributor and make sure there is a good contact, I assume that I'll have to reset the timing and verify that I have the 10 degree BTDC @ 600 RPM afterwards.


Any help would be appreciated.

[JimN]

Do you know about the paper clip method of reading codes on GM cars? Look for the DLC (Data Link Connector) at the rear of your motor, near the ECM. Remove the plastic cover and look for terminals A and B. Insert the paperclip into both terminals, start the motor and rev it to 1000 RPM. Set/verify your timing, snug the bolt and check it again. If it's at 10 degrees BTDC, tighten the bolt and your timing will be correct. You should also see the check engine light flashing- if it only flashes 12 (one flash, short pause, two flashes, longer pause), you have no stored codes. Initially, it will flash 12 three times, then it shows whatever codes are stored and flashes 12, three times before repeating.

If you only remove the bolt and clamp, you won't have to do anything with the timing, but the first thing they told us at MC training was that we should always check the timing when we set up boats for delivery. Trouble is, not all dealers bother to do this.

[fentong]

Great JimN thanks.

So it sounds like I only pull a cap off (not separate a connector) and insert the jumper in A and B. I don't imagine that an OBDII reader could fit into this connector would it? I was just wondering when you mentioned about reading codes using the Check Engine light.

So the plan is (with retest at each step):

Test with reving in Neutral and boat stationary
Check ground of all connectors
Check / clean ground of pickup in Dist
Check / clean ground of Dist
Insert new pickup if all else checks out ok and bounce remains.

[JimN]

If you can get an OBD I reader, it'll work fine. IIRC, OBD II uses two pairs and I don't want to recommend using that if it will connect two leads that shouldn't be. I use a paper clip on my truck whenever I want to check for codes and when I checked my timing.

Connecting terminals A and B will cause the check engine light to flash in that sequence if the wire is continuous from the ECM to the dash. If the wire isn't, it needs to be connected. This won't have any effect on putting the ECM into service mode, though.

[fentong]

I went out on the boat this weekend and without doing anything the bouncing tack symptoms were gone!!
Therefore, it must be a bad connection or something and I'll continue to follow the direction to check the ground at the distributor and the pickup. I wanted to drive it a few times to see if it reappeared but it hasn't so far.