5.7L TBI (1994)- No Injector Pulse

[CatawbaRinker]

Long story short I had to have a rebuilt engine installed in my boat, original engine is a 1994 5.7L Bravo TBI, serial # OF286058. After installing, my mechanic says he isn't getting fuel in the injectors. He pretty much said that after 10 hours of trying to diagnose it, he's done. However is letting us use his shop to continue trying to diagnose ourselves. I raised the question of just trying to settle up and take elsewhere, but I don't necessarily have the funds for 2 engine pulls/installs. However he is now showing no initiative to get it done and here we are in July and my boat has seen no water.


So far we have replaced ignition control module in the distributor (twice actually), throttle position sensor, distributor cap, rotor, both batteries. It sparks and fires when you add starting fluid. The injectors have power, fuel pressure is at 13 (TBI shouldn't exceed 15), tps sends signal back to ECM. We sent ECM to Bob at OBD Diagnostics who confirmed that ECM is good and sent it back along with his ScannerPro and hookup.

However, when hooking this up to a MEFI-1 scanning tool, we notice upon cranking there are no RPM's on the tach. We have tested ground wire after ground wire as well as all hookups. We have double checked all wires and recently rebuilt the injectors. Grounds are correct and everything elseielse and out of the ECM If you turn the key and ground injectors, they spray gas. Something is not triggering RPM when cranking to tell the ECM to ground the injectors. At this point we are lost. I've gotten so desperate I ponied up $1300 for a new ECM as the tech continued to insist that is what it had to be, even after the diagnostics by OBD.

Any other ideas?

 

[Fun Times]

Since you're not seeing an RPM signal at crank it sounds like possibly the distributor coil pickup that sits on the distributor shaft under the rotor isn't working correctly...The distributor coil pickup is the starting point of the distributor efi pulse-width that gives the injectors, tachometer and many other component the signal to fire/pulse. To replace the inner pick-up coil the distributor needs to be removed from the engine and completely torn down. The pickup coil is item number 8, https://www.mercruiserparts.com/bam/.../31869/1953/40

Also as a test, 'Be sure the gray wire off the back side or tachometer gets disconnected as a shorted out tachometer or the wire heading back to the coil or ECM depending on system design could prevent the system from pulsing properly.

Also there is a diode type device hidden inline of the pink? wire that runs between the ignition coil and distributor and should it become compromised it could keep the engine from starting...The wire harness is item number 17 in the parts link above.

Try starting the engine bypassing the boats wiring harness system so you know if the issue is at the engine or to the boat side...Here's a how to video for a quick general guide,

In the following videos, Skip ahead to get to the parts you'd want to see for the helpful guides for testing and replacement procedure ideas of the distributor plus maybe search online 'How to test gm distributor pickup coil' for way more info.

Then see right around the 10:00 + minute mark to see the distributor tare down steps,

First see the 4:00 minute mark for how he used an LED light to test,

 

[CatawbaRinker]

Fun Times,

Thank you for the response. I've actually replaced the pickup coil twice already as that has been sort of a consensus place to start. We have also tested the wiring harness in between the distributor and the ECM and the distributor to the coil (and then replaced the coil while we were at it.

At this point it really seems to be some sort of wiring issue. I appreciate the info on the gray wire off of the tachometer and the video for bypassing the wiring harness. Gives us some additional direction to test out today!

 

[Fun Times]

CatawbaRinker , Since the engine wiring harness was removed and replaced then usually that could be a weak point for a bad connection, pinched wire, broken eye terminal, wire not connected at all or a wire pin pulled out just slightly of the ECM plug connectors...If you're adding a ground to the negative side of the injector system and getting a injector pulse width of any kind then that ought to mean you're missing a ground someplace especially knowing the ECM is good sending it's signal...It's just not reaching it/the injectors and what else isn't turning on?.

Does the fuel pump turn on at normal first key-up? Plus are there any warning horn sounds at first key-up too?
Or do you get those once you add your own ground wire and get the fuel spray?

Ensure the ground wires at the rear of the engine are all connected...I think there are 2 or 3 grounds that come out of the wiring harness and connect the engine block/bell-housing studs and bolts...Some of the black wires are small/thin and a thicker one too.

Another possibility that may have been over looked being a Bravo drive is the White wire coming off of the 4 prong side of the distributor module as seen in the image below would be a missing or misconnected Mercruiser inline jumper connector wire shunt as that is part of the ignition shift interrupter switch some models use. Make sure the connector is there and maybe try testing the wiring side and plug connector if at all possible....The connector is item # 10, https://www.mercruiserparts.com/bam/.../31869/1953/50

If your tech hasn't yet, Hope you both can get together and try starting the engine at the engine's main wiring harness cannon plug like in the video so you know if the issue is the boat side or engine side.
Let us know what you can of all these thoughts, good luck.

 

[CatawbaRinker]

Fun Times thank you for the valuable information. We didn't get a chance to try the plug start, however the boat does fire when you pour starting fluid into the throttle body. It runs until the starter fluid.

Yesterday we hooked up an additional tachometer thinking and short there might be an issue but still experienced the same problem.

When you turn the key the fuel pump does turn on, engine cranks however there is no RPM. Even on the Scanner Pro hooked to the ECM test plug we have tested that there is no RPM. Obviously the ECM needs to see RPM in order to want to fire.

We have spent quite a bit of time on the 4 wires coming off of the distributor. In regards to the white wire, we were sort of confused as to what this was at first. Upon finding it, we found that the plastic part was actually melted so we thought we found the issue, however it continues to flow voltage through it. I attached a picture of it, is there a specific way to test this? Would this be more of an overall timing issue or could it prevent RPM's?

 

[Fun Times]

Try finding one, Borrowing one from an earlier model Bravo engine around your year model if possible or preferably a white wire design as some are shaped differently as they've had a few different part numbers over the years plus I don't believe they'll interchange or work properly. If it's damaged on the inside too it may not make the correct connections even though your test multimeter may show some continuity while performing an ohms test.

It's what the Alpha stern drives uses to interrupter the ignition system while shifting...It affects the RPM signal as the distributor module communicates with the ECM on out.

https://www.ebay.com/itm/0650P8-NEW...8IAAOSwasBe0zod:sc:USPSFirstClass!92555!US!-1

https://www.ebay.com/itm/Mercruiser...nector-Cap-Jumper-Tool-864337a1-/283370150411