Perplexing 5.7GSI PEFS Fuel Problem Wont start - good fuel pressure & clean injectors

nunnink23

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Update from today:

I checked power at the ecm, and I have proper voltage. Checked the three ground wires from the ecm, which merge into one, and they are good. Checked all my other grounds, less than .3 ohms. All good.

Another thing I've noticed is the traditional beep beep when you turn the key is absent on the first key in of the day. The even stranger part is that after sitting overnight, it will ALWAYS roar to life for about 2 seconds after cranking. Then it dies with absolutely no chance of getting a sneeze out of it again for 24 hours, unless supplementing fuel.

At this point I think it's my ecm. I'm nervous since that's two times in three years. I am sending it to OBD ii diagnostics in CA. He seems very knowledgeable, and he will test my ECM, and if it's bad, fix it or replace it. I really don't want to spend 2700 on an mefi 4 with a messy harness.

If the ECM checks out, I'm going to pull the harness out and peel off all the tape, then check every last wire. I also ordered a new ignition module, and while I'm at it, a new coil.

This thing better purr like a kitten when it's done! Just finished an engine refresh over the winter... New oil pump, gaskets, water pumps, valves lapped, stem seals, etc. everything else was within spec so I didn't touch it.
 

Tail_Gunner

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I dont have to much time right now but its not your ecm, check the voltage to the tbi injector's it should be 12 volts. The tbi injector power is not a 5volt rail.and your diag tool would have read check sum error.

https://www.obd2allinone.com/mefiecms.asp...for reference pricing
 
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nunnink23

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I dont have to much time right now but its not your ecm, check the voltage to the tbi injector's it should be 12 volts. The tbi injector power is not a 5volt rail.and your diag tool would have read check sum error.

https://www.obd2allinone.com/mefiecms.asp...for reference pricing

Damn, I already sent the ECM out. I don't remember if the injectors have constant power to one side, or if it pulses?

I know the ECM connects it to ground to get them to fire. If there is constant voltage I can check it while the Ecm is out.

He is just checking the ECM for now. Assuming it passes tests, which I guess it will, then I'm back to the drawing board. Hopefully it's the ignition module or coil then.
 

Tail_Gunner

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Yes the power does pulse in ms and it 12volts... the ecm tells the injector to fire by shorting the 12 volts to ground..In other words since your injectors are firing the ecm is directing traffic so to speak it Gorunds the circut.....now if there is not 12v present then you you wont get full duty cycle at the injector. Read the schematics starting on 35 you have a delco est i assume...merc or volvo the operation of mefi is constant just a few components are different (DIST)

I would think a analogue meter would be so slow it should show average voltage...Maybe Bruce will pop in there should be some way to short that circut manualy and determine the true voltage.....I for one have know ideal circuts and me dont get along at all But you should be able to put the hot lead on the injector plug and ground to the block for a voltage reading...Take heed here wait for a pro to do this.

I can tell you your ecm is just a eprom very basic and if it can read map sensors tps senors and it's working..that is ive never heard of a eprom only working @ 50% but who know's....have your cleaned and checked all your grounds that is what complete's the circut. Have you measured the ohm resistance to your injectors it should be 1 to 1.4 take little for granted.
 
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nunnink23

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Yes the power does pulse in ms and it 12volts... the ecm tells the injector to fire by shorting the 12 volts to ground..In other words since your injectors are firing the ecm is directing traffic so to speak it Gorunds the circut.....now if there is not 12v present then you you wont get full duty cycle at the injector. Read the schematics starting on 35 you have a delco est i assume...merc or volvo the operation of mefi is constant just a few components are different (DIST)

I would think a analogue meter would be so slow it should show average voltage...Maybe Bruce will pop in there should be some way to short that circut manualy and determine the true voltage.....I for one have know ideal circuts and me dont get along at all But you should be able to put the hot lead on the injector plug and ground to the block for a voltage reading...Take heed here wait for a pro to do this.

I can tell you your ecm is just a eprom very basic and if it can read map sensors tps senors and it's working..that is ive never heard of a eprom only working @ 50% but who know's....have your cleaned and checked all your grounds that is what complete's the circut. Have you measured the ohm resistance to your injectors it should be 1 to 1.4 take little for granted.


Thanks for all your help so far. I have check grounds. .5 ohms at all ground locations.

I did not measure the resistance from the injectors to the ECM, nor have I read the actual injectors resistance, although they have now been flow tested by two companies.

Once I hear back about my ECM, it will at least keep me from spending the money on that. In the meantime I have a new Sierra ignition module and coil on the way this afternoon, which I will have on when the ECM returns.

You are correct though, my multi meter couldn't keep up with the injector pulse. If it still doesn't pulse enough fuel after all this, then the problem has to be wiring. If so I will pull the harness and check all the leads related to the injector circuit.
 

nunnink23

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Just heard back from obd II diagnostics. My ECM is good. Still doesn't explain the erratic codes, but it does turn up an interesting find. I have an MEFI 4B computer. The wiring harness has an intermediate conversion harness. I was always wondering why it needed that extra harness.

I guess my next step is to check all the wires in the conversion harness, and then check all the wires in the main harness.

Does anyone know how to verify that I am receiving 12v at the injector leads? Tailgunner, as you said there must be some way to verify this, because a voltmeter won't read fast enough.
 

bruceb58

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Your injectors are supplied 12V on one side and the ECM grounds out the other side. One side of the injectors should read 12V once the relay is engaged. I would probably bypass that relay as a test.
 

nunnink23

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Your injectors are supplied 12V on one side and the ECM grounds out the other side. One side of the injectors should read 12V once the relay is engaged. I would probably bypass that relay as a test.

Which relays? Not the two in front of the TBI right? I thought those were for the fuel pumps. If I am missing a relay, how should I bypass it to check the voltage?

I wasn't aware of any relay for the injectors. I thought it was basically a wire coming out of the back of the ignition module/coil (don't remember which one), which pulses 12v to the injectors and ECM each time it pulses spark. Then the ECM receives that voltage and recognizes the input as RPM's and connects the injectors to ground.

That would mean the injectors would not have constant 12V at the hot side, but rather a pulse of 12V right?
 

nunnink23

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I just looked at the circuit diagram and found out that yours may not be this way. Looks like the ECM supplies the 12V now and the second relay isn't even used.

http://boatinfo.no/lib/volvo/manuals/ef_wiring.html#/12


I thought the coil provided the power? I am not sure which way the electricity flows in that diagram, but I thought it was from the coil (purple wire), which then is spliced into two pink/white wires, one of which goes to the ECM, and the other to both injectors. This is what I thought was the hot side. The other part of the pink wire going to the ECM is something else, im not sure what it does.

Then I thought the other two wires that come off the injectors and lead to the ECM function as grounds when the ECM connects it to ground.

Do I have this backwards? Does current flow from the ECM through those two tan wires to the injectors? And then ground at the coil?
 

bruceb58

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The pink/white to the injectors and the purple wire to the coil are +12V when you turn your ignition on. They are a constant 12V.
 

Tail_Gunner

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Know you may understand why i do not like circutry...It certainly appears (coil) to be a power source not a ground point just take a reading from the node. Pull your relays also they corrode or least mind corrode quite a bit.
 

nunnink23

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So can I take a multi meter and measure between the pink wire and engine block ground? A multi meter won't complete the circuit and cause the injector to fire right?
 

Tail_Gunner

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So can I take a multi meter and measure between the pink wire and engine block ground? A multi meter won't complete the circuit and cause the injector to fire right?


Yes should be the answer the coil does not fluctuate the ecm does the switching or pulsing. I dont see how the injector could fire but i would take a read from the coil and the injector plug for continuity it sounds like your chasing a bad ground some place,,cross your finger's.
 

bruceb58

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Know you may understand why i do not like circutry...It certainly appears (coil) to be a power source not a ground point just take a reading from the node. Pull your relays also they corrode or least mind corrode quite a bit.

That purple wire going to the coil is the 12V INPUT going into the coil. The coil is NOT the power source.
 

bruceb58

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So can I take a multi meter and measure between the pink wire and engine block ground? A multi meter won't complete the circuit and cause the injector to fire right?
Yes. You should definitely do that. Should be solid 12V at all times.
 

nunnink23

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That purple wire going to the coil is the 12V INPUT going into the coil. The coil is NOT the power source.


Ah, so the pink wire coming out of J2 is power then? And this wire is spliced with the purple wire to the coil? So this means that J2 powers both the coil, and the injectors from that pink wire? And then the grey wire on the coil connector is part of the ignition switch? So I will check for power to the coil, and from the coil (pink wire). Then I will check for resistance from the injector grounds to the harness adapter, and then from the harness adapter to the ECM.

The guys at OBD II diagnostics thinks the problem will be located in the MEFI III to MEFI IV adapter harness.

If it turns out to be wiring, then I guess it was due to the harness being disturbed during the engine rebuild process.
 

bruceb58

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To me its strange that the ECM supplies the power to both of these but that is what it shows in the schematic. In earlier years it was supplied by the relay next to the fuel pump relay.

The fact that you were able to put some fuel into the intake and have it run indicates the coil is getting powered. Would still be interesting to see what that voltage is. Pulling off the connector is probably not the best way to test it though since it isn't being loaded. I would pull one of the connectors off the injectors and test the voltage there. That way the coil is still putting a load on the circuit
 
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