4.3L Mercruiser stalls and backfires at apprx. 2,200 rpm

[adm7789]

[h=1][/h] Hello all,
This is my first post on iBoats, so please pardon me if I have not provided sufficient information and thanks for the help in advance.

I am having an issue with my 2001 Chaparral 180 SSE and I'm hoping to get some input on it, as I am not sure what could be contributing to the issue. Below are the details for the engine/sterndrive:

4.3L (GEN +) (2 BBL.) GM 262 V-6 1998 - 0L010044 THRU 0M614999

4.3L ALPHA/BRAVO (262 CID - GEN +)

I purchased the boat with some problems in 2017 and the last registration was in 2013, so I believe the boat had been sitting with the cracked intake manifold, described below, for this period of time. The boat/engine/sterndrive has 88 original hours.

I purchased the boat and was told that the head gaskets, starter, impeller, and spark plugs were recently replaced because water was getting into the oil. I replaced the fuel and started the boat, only to find out that water was still getting into the oil at a rapid rate. I turned off the engine immediately and started to disassemble the engine to find that the intake manifold had crack in the bottom of it from improper winterization. (The previous owner’s mechanic actually pulled the intake manifold off to replace the head gaskets without noticing this….) I don’t believe the engine needed new head gaskets. When I discovered this, I picked up a used intake manifold (OEM) that was in great shape and reinstalled. I torqued everything to spec and changed the oil and filter (3) three times after running the engine and draining the oil each time. I started the engine and all was well, no more water in the oil. However, I was still having the issue of the engine stalling and backfiring above 2,000-2,200 RPM. When I replaced the intake manifold, I moved the engine out of time by mistake. So I put the ignition system in base timing mode and reset the timing to 8° BTDC, per the manufacturer specs. The boat idled continued to idle rough and shut off, so I proceeded to replace the obvious wear and tear items for a boat that had been sitting for 4 years. Below is a list of what I have done and/or replaced on the engine to remedy the issue.
Replaced parts:

• Spark plugs
• Rotor cap
• Rotor
• Spark plug wires
• Tried two different used coils that seemed to be in good shape
• Rebuilt carburetor with sierra aftermarket kit and made adjustments according to specs
• Fuel pump
• Fuel/water separator
• Emptied fuel tank and checked pickup
• Trim solenoids (unrelated to issue)
• Ignition switch (unrelated to issue)

I have also replaced all fluids with the manufacturer recommended brands and capacities and greased all recommended areas.
I started the engine after all replacement parts/fluids have been installed, but I am still having an issue with the engine stalling/backfiring above 2,000-2,200 RPM. The engine does this on the muffs (I do not rev the engine very high on the hose) and at the lake under load.
It should be noted that when I placed the engine in base timing mode, I did not notice a change in idle as some have described in the forums. But I did double check the timing and it seems to be spot on and the engine starts very well and idles well. The engine seems to be burning a rich air/fuel mixture and my thoughts are that maybe the carb is not adjusted properly, but I have rebuilt the carb and set the float and all idle screws to spec. The raw fuel smell is very strong while the engine is running on hose or at the lake, so I drove it enough to know that I’m having the same issue on the lake under load as running the engine on the hose and loaded it back up.
If anyone has experienced an issue similar to my situation or has any input. All advice would be greatly appreciated.
Thanks,
AG

 

[alldodge]

Back firing is either running lean, damaged valve or valve spring, incorrect timing.

Your smelling fuel so could be carb is flooding, with it running look down the carb (safety glasses) and also right after its shut off.

Suggest start with compression test, if that's good the leak down test

 

[Bondo]

Back firing is either running lean, damaged valve or valve spring, incorrect timing.

Ayuh,.... Welcome Aboard,...... I agree with AD,.... 'n if it only breaks up at hi-rpms, I'd think bad fuel delivery,.....

 

[adm7789]

Thanks for the responses. I will do a compression test to (hopefully) rule out a damaged valve. Could bad carb adjustments cause flooding at idle and poor full delivery at higher rpm? I plan to go back through the carb to check all preliminary adjustments. Also, can anyone describe the fuel delivery that I should see in the carb at startup, at idle, when pushing the throttle below 2000 rpm, above 2000 rpm, etc? I can see the fuel spray in if I pump the throttle, however, I have not monitored the carb when pushing the throttle or under load.

As for the timing, I connected the base timing wire to the battery ground with the engine on, but I did not notice a change in rpm. How can I be sure that the engine is in base timing mode? The engine starts well, and the idle rpm is within spec.

I also forgot to include in the previous post that the last three (3) times that I shut the engine off st the ignition, the engine continued to run for apprx. 5-10 seconds.
Thanks again for all of the input.
AG

 

[Rick Stephens]

Without putting it in to base timing mode, using an advance type timing light, you should see the timing run something like 11 to 26 degrees as you ramp up the RPMs from idle to around 2500. Don't run on muffs up there for more than a tiny bit, you can exceed the cooling capability. But at least you can tell if your timing module is advancing properly.

 

[alldodge]

I also forgot to include in the previous post that the last three (3) times that I shut the engine off st the ignition, the engine continued to run for apprx. 5-10 seconds.

This is called Run On and a symptom of running to rich and/or timing is off

How can I be sure that the engine is in base timing mode?

With lead connected you should be able to increase rpm but the timing will not change

 

[Bondo]

I also forgot to include in the previous post that the last three (3) times that I shut the engine off st the ignition, the engine continued to run for apprx. 5-10 seconds.

Ayuh,....Dieseling, or Run-on as AD says,......

When it does that, Turn the key back on, 'n let it idle longer, to cool down more, or throw it into gear, 'n turn the key off, to quickly stall the motor,......
Ya Don't wanta let it diesel to death,.....
That funny sound ya hear, just as it finally dies, 'n the carb might whistle,..??..??
That's the motor spinnin' Backwards,..... Which is the quickest way possible to suck water up the exhaust, into the cylinders, bendin' the connectin' rods in the motor, resultin' in a 500 lb. Anchor,.....

 

[adm7789]

Thanks everyone and I've definitely noted to turn the key back on to let it cool off more if run-on occurs. I'm familiar with the term 'dieseling' but for some reason it did not dawn on my that it could suck water in through the exhaust. Very good reminder. The boat is operating at +/- 210 F (on hose or in lake), which I thought to be an acceptable maximum operating temperature in fresh water, but now I'm thinking this is what is causing the run-on/dieseling. I guess I'll go thought the coolant system to track down the issue. I found out that the previous owner was installing GM parts, so he might have installed a 210F thermostat(seems high, even for a car).
Also, he did install head gaskets that were made for a car, does anyone think that this may contribute to any of these issues?

I'm still confused as to why every symptom points to the engine running rich, but the engine seems like it is starved for fuel at 2,000+ rpm.

 

[alldodge]

operating at +/- 210 F (on hose or in lake),

The boat should run no more then 170 degrees. Should have a 140 thermostat but could also use a 160 in fresh water.

install head gaskets that were made for a car,

Should be OK so long as they were good gaskets, but that is unknown

I'm still confused as to why every symptom points to the engine running rich, but the engine seems like it is starved for fuel at 2,000+ rpm.

Did know the 210, so running this hot can also cause similar issues

 

[adm7789]

I removed and disassembled the carburetor this weekend. The float and the accelerator rod were not adjusted to specifications, so I corrected this and readjusted the throttle cable. The engine will now rev to 3,000 rpm on the hose(did this momentarily), but then the engine begins to shudder again similarly to previously doing this at 2,200 rpm. So I’m thinking that the engine will do this on the lake as well.
I believe I also discovered why the engine was running at 210F, I removed the thermostat and found that someone (before my ownership) installed a 195F thermostat. I’ll be replacing this as well.
My thoughts are that the ECM is not entering into base timing mode when I ground out the pur/wht wire as suggested by the steps in the Mercruiser manual. When I rev the engine, the timing advances regardless of whether or not the pur/wht wire is grounded. AD stated that the timing will not change with the jumper wire connected; however, I confirmed that my timing is changing with the jumper connected when increasing throttle. I think the issue is that the engine is still out of time. Any thoughts? It should also be noted that I grounded the jumper wire to the negative terminal on the battery since this is directly connected to the engine block. Is this acceptable?
Thanks for any input,
AG

 

[alldodge]

As a double check see how much advance your getting without the base wire attached

 

[alldodge]

Also ring out the connections with the connectors

View attachment TB-4 and 5 Ign System.pdf

 

[Bondo]

I'm still confused as to why every symptom points to the engine running rich, but the engine seems like it is starved for fuel at 2,000+ rpm.

Ayuh,..... Carbs do different things through different circuits,.....

There's the low-speed/idle circuit, the mid-range transition, 'n the high-speed circuit,....

The low-speed circuit is helped by the choke on cold starts,....
The accelerator pump helps with the transition from the low-speed circuit, to the high-speed circuit,.....
'n everything has to work in unison,..... All the time,.....

 

[adm7789]

The boat is not with me, but I do have some pictures and recall of the knock sensor not being installed where the manual shows it. For the ECM, there is a single solid state unit mounted to my starboard side exhaust manifold rather than mounted on the distributor as shown in the manual. The unit has two wiring harness, so is the unit a combined ignition control module and knock control module. Is there such a thing? Also, I recall looking for the knock sensor and mine is gone(looks to be plugged or broken off). Could it be installed somewhere else on the engine? Do all Thunderbolt V ignitions have a knock sensor module and sensor? Could someone have attempted to bypass this? Also, can no input from the knock sensor be causing the engine timing to retard or kill the spark completely when throttle is increased?

Thanks for the advice, as this is helping me get to the cause of my problem

 

[adm7789]

Correction - the ICM is mounted on the port side exhaust manifold. If I

 

[alldodge]

Some are on the distributor and others on the riser, and it makes no difference. Not all have a knock sensor and if it did and was removed it would have no impact on running.

 

[TurtleTamer]

Not going into base mode is troubling. I'd chase that down before too much more troubleshooting elsewhere. Retarded timing at RPM is going to give you issues. If you can rule that out then maybe check your fuel pressure as a weakening pump can run fine at idle/low rpm and start to starve you up top.

 

[adm7789]

Thanks AD, that is good to know. I agree with you Tamer on the timing, but have no clue as to why the ICM will not enter base timing mode. Also the fuel pump is new, but I probably should check the fuel pressure in case.

 

[adm7789]

Can anyone tell me what the this component is? Please see attached photo. I have circled the part in question. Also, I grounded the ICM lead to the stud that comes out of the bell housing. I even checked for continuity between the ICM wiring harness pin and where the ground wire attaches to the engine. I had continuity, however the timing is still advancing when I push the throttle. Does anyone else have any ideas as to why the timing is still advancing with the jumper wire connected to ground?

Thanks in advance everyone.

 

[alldodge]

That is the 2GC power piston