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1996 454 Crusader XL TBI Stalling Issue

390Express

Regular Contributor
I have a 1996 Trojan Express. The port motor runs fine, the starboard motor ran fine, until it developed the following issue at the end of last year:

Turn key to ready, fuel pump kicks on, start the motor, motor starts, runs fine, then shuts off in about 10-15 seconds. Starts back up immediately, but always shuts back off. Last year the timing was jumping around, and I knew the distributor was on its way out. Boat has a new distributor, new coil, and has fuel pressure and injectors fire as its stalling.

The wires at the helm have been eliminated from the potential problem source, via swapping the wiring harness at the helm. Tried swapping ECU's, no difference.

Any other ideas as to what it could be, in terms of a sensor or wire stopping ignition from the ECU? I removed and cleaned all ground cables. I haven't been inside the main fuse panel to clean those connections or to mess with the relay. That said, I don't think that's the source of the problem, as the fuel pump and TBI continue to fire as the motor is shutting down.
 
if you are confident in you assessment of the fuel system, the ignition systems is all that remains....was the new distributor 'complete'?

Have you verified spark still occurs?

have you checked the ECU for any stored codes?
 
if you are confident in you assessment of the fuel system, the ignition systems is all that remains....was the new distributor 'complete'?

Have you verified spark still occurs?

have you checked the ECU for any stored codes?

Thanks for the reply Mako.

I have not checked the ECU for stored fault codes, (I don't have a scanner/reader) but I did swap the ECU with the port motor. The port motor runs flawlessly with the starboard ECU, and the starboard motor has the same issue with the Port ECU. The motors are both standard rotation motors, the ECUs are interchangeable.

The new distributor was a brand new A/C Delco, factory distributor, with new module, cap and rotor. The motor starts and runs perfect for the 10-20 seconds that it stays running. It has spark upon startup, but for some reason the ignition (but not the ECU) seems to be shutting down just moments after starting. I know for sure that it has fuel, I'm wondering two things:

1) is there a sensor on the motor that would cut spark, but not cut fuel pump/fuel pressure or TBI injector pulse?

2) is the coolant temp sensor like an automotive sensor, that could potentially be flooding the motor? It's my understanding that faulty automotive coolant temp sensors read -44 degrees when they go bad, and flood the motor out and stall it. I'm wondering if I'm dealing with the same issue.
 
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for #1, I'd say very possible - you'll have to go thru the MEFI1 (or 2) manual to be sure. Most of the early MEFI computers don't monitor the oil pressure for controlling the fuel pump - they use a dedicated switch & circuitry...that said there was a lot of configuration changes and not all of the engine marinizers made them at the same time....

For #2, yes, the ECT sensor drives the operating point on the a/f map....they don't always fail to the cold limit. some will fail where they are not longer 'accurate' but still within the high and low limit thus never setting a code - that's where a scanner helps a bunch.

FWIW, there have been a few posts here over the years where there were harness issues with the EST wiring....and then there's the 'undocumented choke' in the coil harness....
 
Seems like I read recently the oil pressure switch serves as a safety switch in event oil pressure don’t build after the motor starts, opens causing shutdown. You might look at it.
 
FWIW, there have been a few posts here over the years where there were harness issues with the EST wiring....and then there's the 'undocumented choke' in the coil harness....

Can you provide more insight here? I did a forum search for my issue, but most of the "fixes" in the threads were simple things, like a new fuel filter.

Am I correct in the following:
ECT (engine coolant temp) sensor - could flood or lean out the motor
Oil Sensor - could cut fuel, not spark
Knock sensor - could retard timing, not cut spark

Does the TBI Crusader have:
ESP (Electric Spark Controller, and if so, where is it at? Could it intermittently cut spark after startup?)
Data Link Conn. (and if so where at, and could it cause the issue?)

I plan on going through and cleaning and testing the relays and their connections today. I can swap the ECT or just buy a new one. Is the ECT the same as an automotive 1996 3/4 Ton truck (like most other parts)? For the $18 I'll just go buy one. Better than monkeying with the good motor.
 
Seems like I read recently the oil pressure switch serves as a safety switch in event oil pressure don’t build after the motor starts, opens causing shutdown. You might look at it.

If I understand correctly, the oil pressure switch cuts power to the fuel pump, not spark. I have fuel pressure while it's stalling.
 
Correct! I pulled the old MEFI-1/2 service manual and the fuel pump relay is controlled by the ECU, via an oil pressure switch.

There is also diagnostic chart A-3 that is recommended for you to start at....I think you are already at the halfway point there as you've eliminated any fuel issues.

Could also be the main relay contacts failing - either replace it or jump it and see what happens.

If you search the www, you will find many downloadable copies without any signup or join requirement....
 
Correct! I pulled the old MEFI-1/2 service manual and the fuel pump relay is controlled by the ECU, via an oil pressure switch.

There is also diagnostic chart A-3 that is recommended for you to start at....I think you are already at the halfway point there as you've eliminated any fuel issues.

Could also be the main relay contacts failing - either replace it or jump it and see what happens.

If you search the www, you will find many downloadable copies without any signup or join requirement....


Thanks Mako

Update:
Opened up the breaker box. All breakers have 13.8v on both sides of the breaker, before start up, while running, and during the stalling issue.

Boat has power to the coil, and spark as its stalling.

Not sure where to look next. I’m guessing I’ll have to put a scanner on it and see what it’s saying?
 
maybe a test light - with an old 1156 bulb - would be of benefit, here...… there may be a bad connection where the current is limited but the voltage never sags (for long enough that a DVM sees it???

may not hurt to pop the ECU harness connectors and apply some NYOGEL to the socket sides.....
 
maybe a test light - with an old 1156 bulb - would be of benefit, here...… there may be a bad connection where the current is limited but the voltage never sags (for long enough that a DVM sees it???

may not hurt to pop the ECU harness connectors and apply some NYOGEL to the socket sides.....

My voltage meter is pretty sweet. It's a Matco test light with a volts meter incorporated. I had a multi-meter as well, but the light is my go-to.

I don't understand how I can have fuel and spark, but still have a stall situation?

The scanner did pull a code for a faulty Engine Coolant Temp sensor. I'm hoping the sensor was messing up the air/fuel mixture and flooding the motor or just wigging out the ECU. The sensor was reading -39 degrees, when the ambient air temp (and likely the coolant temp) was around 85.
 
Technology is neat - how much current is required to turn the light on?

I don't see how you have the stall with fuel & spark either....something has to be dropping out.

that big of an offset will definitely fatten up the A/F ratio....the ECT is just a thermistor and the MEFI manual provides the resistance vs temp graph (sampled though)...assuming you are going to replace it, there's two approaches you could use until the new part arrives - just unplug the ECT - the ECU will use a nominal default value so the engine should run though not optimally....the other is to lookup the resistance for the nominal operating temp (160deg F) and use a fixed resistor....just food for thought....
 
Technology is neat - how much current is required to turn the light on?

I don't see how you have the stall with fuel & spark either....something has to be dropping out.

that big of an offset will definitely fatten up the A/F ratio....the ECT is just a thermistor and the MEFI manual provides the resistance vs temp graph (sampled though)...assuming you are going to replace it, there's two approaches you could use until the new part arrives - just unplug the ECT - the ECU will use a nominal default value so the engine should run though not optimally....the other is to lookup the resistance for the nominal operating temp (160deg F) and use a fixed resistor....just food for thought....

Thankfully, parts are pretty easy to come by around here. I paid a box store premium, but it's better than waiting 2-6 days from the interwebs.

Put on the new ECT, no change. Runs for 10-30 seconds, then stalls. Changed the top fuel filter just for the hell of it, took apart the antisiphon valve just to rule it out, and change the filter in the 110a Racor as well, no change.

If it was a loss of power to the ECU, you'd think you'd lose power at the coil/distributor. I'm truly at a loss at this point.

I do have a scanner at this point. It's not just a code reader, it's an active monitor. Is there a place to look up nominal values for the data it's capable of putting out?

Some are easy to understand (Coolant Temp, no knock sensor, no retard for knock, no power safe mode, throttle position sensor), others, not so much:

Injector pulse, baud rate, intake pressure, fuel flow, etc.
 
Also Nyogelled the ecu connections, which look perfect, as do the engine grounds. 9 pin looks good as well, put some dielectric grease inside it.
 
around here, one of the big box parts houses will give you 25% off, but only if you order on-line then pick it up...

I know the MEFI-3 manual gives you 'nominal values' don't remember if the earlier ones do or not....I would doubt there's any variation on the common parameters.

I'd never make an assumption about power distribution without verifying the content of the factory diagrams.....too many variations....

won't be able to check the video for a couple more hours.....
 
I watched the video a few times...can see the throttle body but don't understand what else is going on - maybe due to lack of audio.....???

if the flashes were from a timing light, they seemed a bit erratic….
 
I watched the video a few times...can see the throttle body but don't understand what else is going on - maybe due to lack of audio.....???

if the flashes were from a timing light, they seemed a bit erratic….

Flashes were from a timing light, with the pickup on the coil wire. I noticed that as well, and asked the mechanic about it. It was his opinion that as the motor was stalling it was stuck on a trigger spot, providing the longer pulse. It looks a lot more controlled when it's hooked up to the #1 cyl.

If it is erratic timing (timing shows good on the gun, but it's tough to tell if it's erratic timing causing the stall, or if the timing is erratic because of the stall...), what do you think would be the culprit? The distributor and coil are both new. Ignition module maybe?
 
the mechanic's explanation does sit very well with me.....

It may appear more controlled when it is slowed down ….. video frame rates don't help there....

Is the timing erratic (varying without reason) or intermittent (missing firing events)? I'm guessing more of the latter than the former. As far as causes, the module is between the pickup coil and the ECU so that's a possibility (especially if its an aftermarket one)….the other known issue with the EST setup is the choke in the coil harness. there are few postings on the www about it as it is never mentioned in ANY of the EST tech data I've seen (from GM or DELCO or any of the OEMs). when they fail, it is usually an intermittent that results. It is in the two wire harness from the coil to the module.
 
Thanks Mako, I'll look into the coil harness. Do they make an aftermarket partial harness? All I'm seeing online is a complete harness for $900+. Once I rule out the tank (plan on running the boat off of a 5 gallon jake tank for my dingy first), the next step may be a wiring harness. All of the sensors appear to be in working order, according to the scanner. All that's left really, is the wiring, or possibly swapping the brand new distributor to rule that out.
 
the coil harness was ~ $20 last time i looked....

If you are talking engine harness, I'm sure there are a few sources but I haven't looked lately...guess a lot is driven by what 'partial' means...if the issue is only a wire or two, I'd think it much more economical to fix what you got...
 
Interesting thread. All of us that have struggled with failures that have true mystery causes enjoy reading them. Always something to learn.

If you have not yet taken the advice to download an MEFI diagnostic manual please do so. Tremendously helpful and by gaining a real understanding of how the system works you can come up all sorts of tests to check out your particular problem.

I believe most (all?) of these MEFI systems use a separate source of power for the fuel pump(s) before startup and after startup. I know that you believe you have seen fuel pressure during the shutdown, but the raw symtoms certainly support the possibility that you have pressure until startup and then gradually lose pressure until the engine quits. You get it back right away as you sit there ignition on but not running. Not saying that is what is happening but I would be very sure of your "no fuel supply problem" observation. The fact (if reported correctly) that it always seems to run about the same amount of time before quitting is, in itself, an important clue. I don't know of many (any?) electrical "loose wire" or failing component faults that have that behaviour mode. I suppose some of the flooding possibilities discussed could fit that behavior but usually fooling with the throttle will keep things going for longer than that (if it is getting too much fuel)....or shorter than that if it is losing fuel pressure.

Since the distributor change happened about the same time, if you have not done so you might swap out the distributor and everything associated with the change over to the other engine. An hour spent doing that will eliminate a great number of possibilities.

Good luck.
 
Interesting thread. All of us that have struggled with failures that have true mystery causes enjoy reading them. Always something to learn.

If you have not yet taken the advice to download an MEFI diagnostic manual please do so. Tremendously helpful and by gaining a real understanding of how the system works you can come up all sorts of tests to check out your particular problem.

I believe most (all?) of these MEFI systems use a separate source of power for the fuel pump(s) before startup and after startup. I know that you believe you have seen fuel pressure during the shutdown, but the raw symtoms certainly support the possibility that you have pressure until startup and then gradually lose pressure until the engine quits. You get it back right away as you sit there ignition on but not running. Not saying that is what is happening but I would be very sure of your "no fuel supply problem" observation. The fact (if reported correctly) that it always seems to run about the same amount of time before quitting is, in itself, an important clue. I don't know of many (any?) electrical "loose wire" or failing component faults that have that behaviour mode. I suppose some of the flooding possibilities discussed could fit that behavior but usually fooling with the throttle will keep things going for longer than that (if it is getting too much fuel)....or shorter than that if it is losing fuel pressure.

Since the distributor change happened about the same time, if you have not done so you might swap out the distributor and everything associated with the change over to the other engine. An hour spent doing that will eliminate a great number of possibilities.

Good luck.

Thanks Cabo, truly maddening. I'm going to investigate the wiring harness, and swap the motor to a 5 gallon jake tank that I usually power my dingy off of. Putting fresh marine gas in the jake, coupled with pulling the return line, and feeding that back to the jake, will allow me to visually see any disruption in fuel flow. I did have a fuel pressure gauge on the shrader valve during shutdown, and the pump maintained a proper 12psi. Also worth noting, the ECU doesn't read a low fuel pressure warning (though, I'm not entirely sure how it monitors the same... it has a "fuel flow" read-out, and it looks normal, until the damn thing shuts off). I really thought that I was out of gas, meaning, I had just enough to touch the pickup and get it started, then it would stall, but I've put in another 30 gallons since. I put new fuel level sending units on this year, set them to 2.5" from the bottom of the tank (24" tank, set the gauges to read empty at 21.5"), and the gauge still reads about 1/4 tank, which I believe to be accurate. Again, however, running from the jake will eliminate any fuel level issues.

The jake and the coil harness are my next targets at this point. I'll definitely keep you posted to let you know what I find. I do have a damn quadrajet on the shelf. As a last resort I could try running it off of a carb, and ruling out EFI issues. I may need a simple fuel pressure regulator ran inline, but it would be easy enough to install a 1' piece of 3/8 rubber and a cheap regulator just to run a quick test.
 
The ECU does not know the fuel pressure (pressure is controlled by the pump and a pressure regulator). It only knows what it should be, and it knows what signals it sent to the fuel injector(s). But it does not know if the injector actually fired and if fuel under pressure was there. So the fuel flow readout is a calculation that is useful in normal times but in your case perhaps not meaningful. But if you saw pressure at the schrader valve and the engine actually started, I too would assume all is well with regard to fuel. You now suspect you have upstream fuel source problems, but that would be shown by a drop in the fuel pressure before engine shutdown. That did not happen so likely you are chasing your tail on messing with a jake, etc. With good fuel pressure, fuel starvation could only occur if the injector quit working. I don't have a theory on why that would happen 10-15 seconds after startup.

Before trying a Quadrajet, I would recommend swapping out (a portion at a time) everything with the other engine and find out which one makes the problem move. (Swap the distributor, swap the coil, swap the throttle body, fuel pump, etc.) You really have messed with it too long and just need a brute force approach, which you can do since you have a known good engine next to it. If you move everything and still can't find the problem then I suppose the wiring theory may be right, but that is not the place to start.

Oh, and get that diagnostic manual.

Good luck.
 
I suppose I could try swapping the throttle body. Boat has a new IAC, MAP sensor, and distributor. Throttle position sensor seems to be working fine. I have a new coil that I plugged in, but didn't end up mounting because it didn't fix the problem.

I tried swapping the ECU, ignition relay and starter relay, obviously no change. I suppose I could swap the MAP sensor, and distributor from a known working source, to rule those out. Injectors spray nicely, even as its stalling (you can see in the video if you watch it while it's stalling, that the injectors spray as it's stalling), but a TBI swap is fairly simple.

I have the diagnostic manual. I'm going to run through it, again, this evening... I'm going to look into the harness from the coil to distributor to see if it's something that's fairly easy to swap side to side. Maybe play with the male pins, per the thread that Mako posted earlier.
 
Swapped the coil to distributor, two wire harness, ignition module, fuel pump relay, and MAP sensor today. I considered swapping the throttle body, or at least the upper half, but I really don't see the advantage. The fuel pressure reads fine, the injectors spray fine, and there's no vacuum leaks. Perviously swapped the ignition relay, & starter relay. IAC and throttle position sensor are operating fine via visual inspection and scanner readout.

Ran the boat off of the dingy tank. No real difference, but it was nice to see fuel pumping as the motor stalled and after. Return line was flowing fine; nice steady stream, no disruption in fuel, brand new marine gas, still stalled... Confirmed that both motors are operating fine off of the same fuel pressure (12psi)

The only real noteworthy item left on the ignition side is the distributor. It's brand damn new, AC delco distributor, cap and rotor, but stranger things have happened than getting a bad electronic device out of the box. Still weird that the coil and module have voltage and spark as its stalling.
 
Pickup coil in the distributor is the data source the ECU uses to determine the engine's operating state....and, sadly, DOA parts with the ST system aren't as rare as they should be...so Cabo's swap suggestion is really timely....
 
Pickup coil in the distributor is the data source the ECU uses to determine the engine's operating state....and, sadly, DOA parts with the ST system aren't as rare as they should be...so Cabo's swap suggestion is really timely....

Real time data stream is fine. Everything looks normal, until it stalls. The issue presents as more of a fuel delivery issue, despite all evidence to the contrary (fuel pressure is good, fuel pump continues to run while stalling, injectors continue to fire as its stalling), so I'm going to try swapping out TBI uppers prior to swapping the distributor. It's about a 30-40min. swap to do both TBIs. This will eliminate the fuel pressure regulator and injectors as potential problems. If that doesn't fix it, I'm going to swap distributors (another 30-40 min. swap). That's really all there is left, besides the wiring harness. After those two potential problems sources are ruled out, I will have literally done every other damn thing I could do, other than internal engine components, and tracing issues at the harness. (recently pulled the 9 pin, and added Nygel... only other electrical component(s) that I could possibly swap are the breakers, but voltage checked out fine from one side of the breaker to the other while it was stalling)
 
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