Help !!!!! with 1994 TBI

Hey guy's I been a correct craft owner for 12 years never a moment's worth of trouble so I guess It's about time. I have a 1994 tbi 351 It will start and run about 3 min and then shut down like you you pulled the kill switch. Let it rest about 20 min and it will start up run about 3 min and shut down again. Fuel pressure is 13 psi (perminantly mounted a guage to monitor). Discount inboard sent me a protech ignition pack still has same problem. What is next computer ? crank sensor ? electrical short ? Should I convert back to a carb/distributer due to the limited supply of TBI parts ? Thanks for your help.

Kevin

what about the fuel pump relays? read alot about guys having to replace them recently.

did he replace the coil pack and not the module? should have tried the module first, if it was a coil pack it would just misfire and not take out the spark all together. When it happens verify the spark is being lost by pulling a plug or wire and looking for the spark.

the coil pack isn't going to go out all at once it will misfire a while before it quits completely and it's extremely rare that two would go out at the same time but it is a motorola design and sucks, that's why they don't make them anymore.

Tim I believe it would or at least go to limp mode but it's not really getting enough time to heat up the oil to thin it out and lower the reading with it occuring in about 3 mins after start up

You guys are fantastic !!! David you've done an excellent job explaining the troubleshooting process and relaying my problem to the rest of the forum. I am leaning towards the faulty key switch due to the fact that I have replaced the coil pack and computer to no avail. This evening, I noticed that the key switch seemed to operate intermittently in the "on" position. When the key is turned to the on position, the fuel pumps should give the engine an initial burst of fuel. However, I found while trying to start the motor several times, that the fuel pumps were not engaging. If I drag the starter, the engine starts and runs at 1200rpms, just like normal. This verifies that the crank position sensor and fuel pump/relays are opreational. So again, I am leaning towards the key switch. What do you think? Stay tuned - will bypa$$ the key switch tomorrow. Thanks again for all your help. I will post when I find out more.

Hey guy's still have not had time to trouble shoot the key switch ( two in dipers + work means it's dark and I'm out of time). I have found a place that may be able to rebuild the ProTech coil pack and ECM. They repair ignition systems and ECM's for merc,omc and mercruiser. They said you have to send them your units to know for sure. The company is CDI- Rapair 256-772-3829 they are located in Madison Alabama.

Kevin

Kevin:

I think you and they will find that the units are not rebuildable. Even the ECM components and board are encapsulated in epoxy.

Just thought I would jump in: See my thread "GT-40 Engine Cuts Out"

Replace the freaking relays, dude. 12.00 each from ski dim. My motor cut in and out. I'd fiddle with the relays, pulled them in and out, it worked then it didn't. Checked fuel pressure, cleaned the screens, etc, etc, etc...I got the new relays: Not one problem since.

That it goes whack when it is hot tells me it is electrical related.

Read the threads on this site and others. An you will see Nautiques have relay problems. Buy 5 and keep them on-board.

To the rest of the forum: way to jump in and help this dude!

KevMan38: If you comb this forum for other people who have had the same problem, you will come up with a list of 50 things you can check. I have done it, and I will say this: 99% of the cut out problems are electrical. Mostly connections, too.

well, I replaced the fuel pump relay still no power to the pumps. I've been over every connection, every ground, combed every wire with in reason looking for a bad spot or short nothing stands out.I can only find one relay. Some are saying that there are two.I still can't find my @#$#@#$$#@#$$#@#$##@# shop manual. Can you tell I'm getting frustrated !!! .When the ignition switch is in the on position I should see 12 volts to the pumps It's not there. New relay and still not there. I don't know the exact pins on the relay to meter... I suspect it would not matter as I have checked all pens to ground.... 0 volts. What am I missing, another relay ? I'm stuck. Still when the switch is held in the start pos the motor runs at 1200 rpm's @ 13 psi upon start up. This tells me cps/fuel pumps/relays are functioning ,but why not in the on /run position ? did I mention I can't find my @#$#@#$#@ manual. If ther are two fuel pump relays on a 1994 pro boss TBI motor I can only find one in the rear by the ignition coil pack. Where is number two ?

Kevin

79 is right. The fuel pumps run a maximum of 5 secs once the key is turned on. The control module (ECM) then shuts the pumps off if no rpm signal received. (the oil pressure switch is not involved). Once the ECM gets a 300 rpm signal from the interupter (trigger) then the fuel pumps relay is pulled in.

I think there are two relays: one for both pumps and one for the ECM (again, I think but might be wrong on this...cannot remember clearly).

The ECM outputs four control functions:
Injectors
Fuel Pump relay
Idle air control
ignition timing

If the ECM is getting bad input from several sources, then it is probably killing one of the outputs listed above. I am still suspecting fuel pumps. However, I believe the ignition timing is also control by the knock sensor. Try disconnecting the single wire from the knock sensor (located in one of the block drains). This will still allow the engine to run, but take a potential faulty sensor out of the equation.

FWIW: ECM inputs are:

Manifold Absolute Pressure (MAP)
Engine speed (RPM)
Throttle Position (TPS)
Water temp
Crankshaft Position
Intake air temp
Barometric Pressure
Battery Voltage
ProTec

Note the ProTec part of the above. The signal is via the green/purple wire (terminal C). make sure this wire has a good clean connection at the disconnect plug.

In my automotive experiences, a faulty crank position sensor is the number one reason for an EFI engine to simply shut down. Although i have been lucky and never had a fuel pump failure, I would suspect the fuel pump failure to also cause a shut down scenario. Unfortunately, the PCM TBI system does not simply have a CPS to replace as it is part of the interupter/trigger/distributor. Also, once the engine shuts down, you should be able to cycle the ignition switch and hear the fuel pumps run for several seconds. If you do not, then focus on the pumps and related electricial components.

And, do not forget about that 15 amp breaker! I suggest you simply bypa$$ the breaker during testing. (the 15 amp breaker with the red wire feeds the pumps and ECM via the 60 amp breaker). Or, you can check the breaker by looking for 12 volts (key on or off) at terminal #30 of the ECM (check after engine shut down...ie hot).

Terminal #87 (yellow wire) of the fuel pump relay is the 12 volt (+) terminal. The injectors get power via the fuel pump plug terminal #87 (red wire) not the relay terminal. So, check the connection at the fuel pump because even if the pumps run, the injector power circuit could be cutting out. The ECM just completes the injector circuits to ground.

I know this post is a little disjointed, but I was typing as I was thinking and reading. Hope it helps.

Here's to the fat lady singing loud and long.

Well did my drive way test.......and I'm sick ! Started fine ran 5 min blah blah blah same story. New ignition switch , fuel pump relay ,jumped 12.5 breaker, tried new ECM and pro tech coil pack. The only thing consistent is heat. I'll look at all the pins and connections again for 12 volts to the pumps and ECM.It has to show it's self. Did I mention that I hate intermittent electrical issues.

Kevin

David, thanks for you help.I may call on you again if thats ok.

Status?

Well, great news. I hope you have it nailed this time for sure. A good lesson/reminder to all of us that wiring can/does fail. Problems within the wiring (not connectors) are the hardest to find.