I need help i have a LT1 corvette motor in a mastercraft wakeboard boat factory converted by Indmar. It will not run under a load it fires right up every time and i can get rpms out of it if i run the throttle up very slowly if you rev it like normal it dies if you dont let off the throttle. In gear in the water(load) no matter how easy you run the throttle i cant get over 1000 rpms.

I have changed the iac, map and the tps. then i bought a scanner program and everything looks good to me Except the fact that the BPW is barley going up its 2ms and does not go up when the engine tries to rev, as it dies it goes to only 4.5 or so. this is with no real load on the engine. things that are different are It is an Indmar LT1 it is basically 90% LT1 the thing they changer are

1 The fuel pump is external(Fuel psi stays around 38 psi if i remember and stays solid when it dies)
2 They took the opti spark off and replaced it with Cadillac north-star and added 2 crank sensors(It still has spark as the engine dies)
3 it has marine exhaust risers with NO O2 sensors

The way i understand it the bpw is controlled by engine load. On my software i cant figure out witch value is engine load

Am i missing something
Thanks in advance

 

What ECM does the engine have? What is BPW?

 

Have you talked to Indmar?

 

https://www.indmar.com/engines/service-advantages/

 

bpw = base pulse width

ECU Not exactly sure it uses MEFI-1 programing wich is Marine Electroic Fuel Injection

INDMAR- I got some info from them this past summer just for troubleshooting and getting my computer hooked up but not for this problem

 

Have you checked fuel system ? Pressure, filters and for contamination. MAP sensor would indicate load. Service manual? Some may have scanner data descriptions and values. High resistance in secondary ignition, typically rust on coil towers, causes multiple problems with Northstar DIS.

 

Yeah the fuel PSI 38PSI and stays solid even when it dies. I have replaced all filters and cleaned the tank. MAP sensor is new. i had all the coils off and replaced 1 that had corrosion on it and tested the other 3 with a meter. The ignition module i took to autozone but they didn't have the right cable to test it. As the engine dies it still has spark on all 8 cylinders

 

Welcome to the Corvette Forum Quintin Cima!

I bought a MAP sensor a few months back from RockAuto and it was defective from the get-go. Don't always assume that "new" parts always work.... One out of 4 new in the box O2 sensors were bad from RockAuto and they gave me a big hassle and would not replace it... or the AC Delco MAP sensor.

I had an engine that would happily start and not rev over 1000 rpm unless you raised the RPM's s-l-o-w-l-y. It was a blocked catalytic converter. Check to be sure that your exhaust has no blockages in its path.
If you do have any rust or corrosion on the Coil Towers try using some DeOxIt on the tops, it removes the corrosion and gives you a good contact surface. DeOxIt is something that belongs in every C4 Tool Box as I find dozens of uses for it on my C4. It might be useful in the marine environment as it stops corrosion and ensures a good connection.

While in College I lived on a 36' Boat in Ft. Myers Florida. It came with a Chrysler 318 that was thirsty and drank over 12 gallons an hour at 12 knots. I pulled the 318 out and installed the first diesel engine I ever worked on, an 85 hp Perkins 4-236. (Four cylinders 236 cubic inches) I then took the same boat and brought it up the east coast to the Washington DC area on less than $300 of diesel. I was able to burn 1.3 gallons an hour at 12 knots. Sure made boating more fun.

Hello Kevova,
I had two of the Northstar engines in two Cadillacs I had. Both of mine developed head gasket issues, one at the dealership while they were testing it. They called me and told me to have my STS hauled off to a junkyard due to head gasket failure. It wasn't bad until they had it in their possession and were working on it. I never had any issues with the DIS on those engines. In the end I wish I had kept the STS and just rebuilt the engine myself. The Cadillac people said it was "not cost effective" to fix the head gaskets on a $60 k car. The big issue was the studs pulling out of the aluminum block, sounds like the same problem we had with air cooled VW's. On "high performance" (its all relative) air cooled engines they tend to want to go "apart" so we always installed "Case Savers" which was essentially installing Heli-Coils in every hole in the block. On a couple high compression engines I actually thru bolted the entire case using long sections of threaded rods.

Best regards,
Chris

 

I have alot of experience with Cadillacs. The possibility of thread pulling including after thread repair with time serts lead to replacement vs repair. Cadillac needed a different alloy and coarse thread head bolts. My experience with fine thread fasteners and aluminum hasn't been good. Thread stripping in the constant. The 4.1-4.9 had aluminum blocks without the thread pulling issues. I had a ETC it was a fun car just couldn't get parts for it. The thing would rev 6300 shifting into second.

Back to the boat. Northstar modules don't have a high failure rate. 93 -97 Northstar at pick and pull best value. New is just too expensive. Grounds and condition of connectors. Condition of crank sensor jumper to ICM. Has boat been in constant service or sitting and waiting.

 

Thanks
Sorry about it being a boat but i have struggled with this all last summer.
As far as i can tell the MAP sensor looks good as far as the values. BUT i am new to the using the real time scanner to watch the engine.

i also pulled the exhaust hoses of and ran it with open manifold and no change.

I could be wrong but i don't think it's the ign. I think the BPW (injector pulse) is way too low for the engine to run under a load but not sure why it wont go up

 

I Have checked all the connections and grounds.Its been sitting for about a year.

 

Hello again, Quintin

Could you post some of the numbers you are seeing from this system? I and I am sure others could offer better help if we could "see" even a screen shot of the information coming from your scanner while it is running before shutting down. What happens when it shuts down? How long does it run and is it consistent?

Also any modifications done by the "conversion folks" to your engine? Do you still have a OBD port on your engine package? Is there any sort of engine protection equipment on this marine Application? Auto shut down if one of the specific sensors does not respond? I ask having installed a system like that on my Boat. A lot of them override normal functions from the control area to protect the engine in a hurry.

Which scanner are you using just out of curiosity? I have the old Actron OBD1, a CR Reader and recently a Snap On MT 2500 from a fellow Corvette Forum Member. The information from the MT-2500 is great, it lets you see what is happening as it happens and on a OBD1 Corvette that is awesome and extremely helpful.

Not to sound dumb but I was wondering if you have changed your fuel filter in a while? You have a positive fuel supply up to shutdown? Does it pop or miss before shutting down? Or is it more like the Key was turned "off" and it immediately shuts down?

I had a Steel fuel supply line corrode closed internally due to the fact it happened to be the low spot in the line and the Ethanol laden gasoline likes to absorb water and start rusting at the low spot. It would flow the right pressure but the supply wasn't there so it would run out of fuel. For get the pressure for a minute and watch the flow, I used a measuring cup and timed the discharge to find my problem... The rubber hose I used in testing bypassing the fuel lines was substantial as it flowed a lot more gasoline and my L98 is happy. Just a thought...

Thanks,
Chris

 

What did the old fuel look like? Filter elements? You could look at injector screens for deposits.

 

I will get the data and try to post it

Indmar Conversion
1 extermanl fuel pump (PSI is 38 steady even when it dies)
2 the opti spark has been removed and replaced with Cadillac north-star ignition, which also added 2 crank sensors
3 No O2 sensors
4 No MAF sensor
5 it uses a MEFI port for data which is Marine Electronic Fuel Injection the scanner is actually my laptop with scanner pro on it

No pop or backfire just the sound of air rushing in,

I cleaned the tank changed the fuel water separator (couldn't really tell how dirty it was) and the high PSI filter also cant tell how dirty it was.The fuel looked good that i pumped out.
i put new plugs in and checked compression around 190 on all 8

i have changed MAP sensor,IAC and TPS

I ran a professional injector cleaner that i borrowed through it NO change
Where are the screens located

 

Screen is at injector inlet, IDK that taking them out to check will show any thing. TPS reading should be .5v to 4.5-5v with smooth transition.

 

1st Snip is idling
2nd one is while it is dying
3rd one show a running test with the top line RPM and the bottom BPW
Ican replay that same run and monitor anything i want and graph it if someone wants to look at something different

 

It appears intake air temperature sensor is disconnected or has failed. I would graph TPS. What does MAP read engine off? Do you have manual or e book?

 

Same run
BLUE is TPS Volts
GREEN is TPS

 

This is engine off
Which one is the intake air temp sensor

 

It does NOT have a MAF and i dont think it has an intake temp sensor. If it does it would have to be in the intake(which i dont remember seeing one) because the flame arrestor clamps directly onto the throttle body