IAC Issue

[knotguilty 6]

Yes, that is my engine. Made the videos last night. Not sure what you mean by cross fire distributor cap. The cap is not Murcruiser. It is a standard 350 small block rotor and cap.

[knotguilty 6]

So back to the fuel pressure. Sounds like replace the fuel regulator on the cooler first and go from there?

[Tommywalton1974 175]

So back to the fuel pressure. Sounds like replace the fuel regulator on the cooler first and go from there?

Ha sorry just looks nothing like my set up. I'm just not sure that fluttering gauge means the regulator is bad. I'm going to get you some video of mine when I put it in the lake.

[knotguilty 6]

I replaced the fuel pressure regulator in the cool fuel box and the fuel pressure looks steady now but is still running high around 38 psi. The idle is still rough, sounds a bit like a Harley in the water. Sounds like "potato potato potato". The exhaust still smells really rich and I get a black layer of soot like stuff all over the hull near the exhausts (Sideswipe). Vacuum is still running low 12 inhg. Which may explain the high fuel pressure and rich idle. Compression looks good. I can't explain the low vacuum. I've measured it straight at the intake manifold and still low. I have a 555 ECM so timing should be good but I checked it with the scan tool and it is bouncing all over at idle. Rpm is also bouncing between 575 and 630. Does anyone know where the ECM gets RPM? Cam position sensor?

 

One more note, I checked the duty cycle at the IAC. The computer and the duty cycle gauge read the same. I tried 2 new IACs and they reacted the same. They didn't move when not on the engine but I have to assume the airflow helps push the actuator.

[knotguilty 6]

I replaced the fuel pressure regulator in the cool fuel box and the fuel pressure looks steady now but is still running high around 38 psi. The idle is still rough, sounds a bit like a Harley in the water. Sounds like "potato potato potato". The exhaust still smells really rich and I get a black layer of soot like stuff all over the hull near the exhausts (Sideswipe). Vacuum is still running low 12 inhg. Which may explain the high fuel pressure and rich idle. Compression looks good. I can't explain the low vacuum. I've measured it straight at the intake manifold and still low. I have a 555 ECM so timing should be good but I checked it with the scan tool and it is bouncing all over at idle. Rpm is also bouncing between 575 and 630. Does anyone know where the ECM gets RPM? Cam position sensor?

 

One more note, I checked the duty cycle at the IAC. The computer and the duty cycle gauge read the same. I tried 2 new IACs and they reacted the same. They didn't move when not on the engine but I have to assume the airflow helps push the actuator.

[knotguilty 6]

Video of my vacuum gauge and RPM on the scan tool. https://youtu.be/XqJKj1Keu5g

[Tommywalton1974 175]

this is just what I know from digging around my engine. I've checked it out pretty good. I know there is a crank sensor in the timing chain cover. I haven't see a camshaft sensor. The ignition is mercruiser thunderbolt. I don't know for sure but I'd bet my money on the crank sensor handles the job of rpm to the Ecm.

http://www.boatfix.com/merc/Servmanl/16/16B4R2.PDF Here is info on the ignition if it's helpful.

It is beginning to sound ignition related.

Maybe check out the knock sensor part. I've seen engine run, but like crap, and have knock sensor issues.

Edited August 9, 2016 by Tommywalton1974

[knotguilty 6]

Problem solved! I did a balance check on my new injectors (500 ms and 20 cycles) fuel pressure dropped 9-10psi. I put the old injectors back in and 8 psi drop. 20% more fuel from the new injectors. Looks like China replacement injectors are not the place to save some dough.

 

I left the old injectors in and went out on the boat all day Sunday. She purred like a mountain lion! No black streak on the side of the boat either!

[Tommywalton1974 175]

Problem solved! I did a balance check on my new injectors (500 ms and 20 cycles) fuel pressure dropped 9-10psi. I put the old injectors back in and 8 psi drop. 20% more fuel from the new injectors. Looks like China replacement injectors are not the place to save some dough.

 

I left the old injectors in and went out on the boat all day Sunday. She purred like a mountain lion! No black streak on the side of the boat either!

You gotta be kidding? Ha well dang no go on the China injectors. Lol

[Tommywalton1974 175]

Wait you put the stuck injector back in also? I guess it's not stuck anymore

[knotguilty 6]

The belief now is that the fuel pressure regulator drove the injectors to force open. I cleaned them all with injector cleaner and did a balance test before hitting the lake. All good so far.

[Tommywalton1974 175]

I'll remember all this.