nbanwart

Long story short, I had a running car, changed out the MAP sensor and hosing, put in a new rack and pinion, put a new oil pan gasket on, did NOT try to start the car, and went on a vacation for 2 weeks to come back to a car that is not spraying fuel through either injector. I believe I have fuel pressure, as gas squirts out the fitting if I loosen the fuel line connector a full turn, however I do not believe the ecm is sending a signal to the injectors as no change in voltage is read when cranking the engine. Any ideas what this could be? Something to do with the new map sensors perhaps? I have no clue as to what the problem is, and would greatly appreciate your input!

skirkland1980

iTrader: (2)

Are you getting spark? I know you're not spraying fuel but that would tell you if the ecm is getting a signal from the distributor.

nbanwart

Be right back with the answer...

nbanwart

Huh. No spark whatsoever...

skirkland1980

iTrader: (2)

Do you hear the fuel pump prime with key on engine off. Check all the fuses. If the fuses are good get a schematic and check power and ground to the ecm. If you have a spare distributor you could try one.

nbanwart

I can hear the fuel pump, and all the fuses are good. Assuming the ecm has power, is there anyway to check the distributer to see if its outputting without putting a new one in?

tzim350HO

Your coil gets a reference from the ICM Igniton Control Module in the distributor. If it does not send a signal to the coil it will not fire. One of the easier things to check before blaming the computer.

tzim350HO

By the way double check your work! Could have pinched a wire somewhere while working on the oil pan. Check all plug in's around the area where you were working on the MAP.

nbanwart

How would you check this though? If it did not send a signal, would this also cause the fuel issue? Sorry for my ignorance, just uneducated with this distributor and fuel injection system.

And already did, I was trying to be painfully meticulous so something like this wouldn't happen

82tarecaro

iTrader: (4)

Did you check for any codes in the computer? If you had an ICM failure it might throw a code. There would also be no reference signal to fire the injectors with a bad ICM.

Dominic Sorresso

You mentioned MAP hose! What about the weather pack connector? Is it seated properly?

82tarecaro

iTrader: (4)

It should still start with the MAP disconnected. It sounds more like a spark/ICM issue, and due to that there is no reference signal to the computer to pulse the injectors.

Dominic Sorresso

The MAP sensor is bolted on a bracket hanging on the firewall. I think I remember that the fuel pump relay is also located there. Check the wiring on both. I was modifying my Xfire and installing a ZF6 trans in the car. While on my back under the car, I looked up and saw bare wire plugging into the MAP and the pump relay. More importantly, its a fire hazard.

kauboy

No change in voltage? Hmmmmm....Where are you testing for voltage? The ECM toggles the ground to the injectors.
No spark no injector pulse probably means no signal from pickup coil to module or no signal from module to ECM, provided that there is power and ground to ECM, ignition module etc..

nbanwart

Well bought a new ICM today because it sounded like that was the problem...the new ICM dd not make a difference whatsoever. Would a bad coil cause both of these symptoms? Are there any fuses not in the fuse box inline with the ecm I should perhaps check?

Additionally, when I jump the AB terminals to attempt to pull codes from the engine nothing happens at all. I'm assuming this means the ecm is not getting any power?

Dominic Sorresso

What about the oil pressure sending unit by the distributor. Cuts off fuel if no oil pressure.

nbanwart

Dash is showing oil pressure (up to 40lbs or so) when cranking...if for some reason that was the problem, it wouldn't explain the no spark though, would it? I don't know though, after the first 2 seconds of fuel pumping, I can't hear the pump anymore.

Dominic Sorresso

Oil pressure sensor for fuel cutoff and gauge sensor are two different sensors IIRC.
The fuel pump will automatically cycle on for 2 sec. then shutoff to prime the TBIs. Question is whether it will come back on based on oil pressure.

kauboy

Might have a fusible link at the starter.

nbanwart

I don't think my car has 2 oil pressure senders, because it has the 3 pronged oil pressure unit that goes to the ecm. But either way there should be enough pressure to fire the injectors a couple times at the least, or so one would think, or at least that makes sense to me.


Couldn't find one at the starter unfortunately. If everybody keeps pitching in ideas i'll have to eventually figure it out

82tarecaro

iTrader: (4)

Did you check the fuse for the ECM? It should be a 10 amp fuse in the fuse block. I know you said you checked all fuses but it might be worth swapping it out. Also, IIRC - I think there is a separate wire at the battery feeding the ECM. I am checking my shop manual.

82tarecaro

iTrader: (4)

There is a fusible link at the battery that feeds the ecm. It is also tied into the oil pressure switch. Make sure that fusible link is OK. You could also test for power at the orange wire at the fuel pump relay, as it is tied into the same power circuit as the ecm.

kauboy

OK. let's start over. Do you have a vette or F body and what year?

nbanwart

Haven't seen a fuse like that, so maybe that's it. I'll check on it and get back to you guys.

It is a 84 Vette.

82tarecaro

iTrader: (4)

OK - might be the same but I was looking in an F body shop manual.

nbanwart

I was looking around the battery area and pulled up (gently) and a wire split in half. I currently have all the same functions on my car as I did before the wire was pulled off, so I wonder if the wire was not internally damaged. Problem is, the wire is stemmed off some sort of plastic connector (no idea what it is), do any of you guys on how to wire this? In the attached picture, it is the now-bare wire.

kauboy

That's your fusible link. If it attaches to that black plastic block in the foreground you found your problem

InfernalVortex

iTrader: (4)

No it does not. It's in a parallel circuit with the fuel pump relay. It's a backup to make sure if your fuel pump relay goes bad you can still get the car running.

nbanwart

Oh...I was looking for a inline fuse, I feel dumb. Could I just replace the fusible link with a inline fuse or does it have to be a fusible link?

kauboy

I'd replace it with the same thing that you're taking out.

nbanwart

Well, replaced the fuse and put everything back together and...nothing. Same problem as before. I checked the voltage on both sides to make sure the fuse was conducting too. Any ideas?

kauboy

Looks like multiple problems. Not very common to have too many things happen at once for no reason. Back to basics i guess.....Recheck your ECM fuse, injector fuses 1 & 2, if good see if check engine light is on with key in run position, jump A b terminals at ALDL to check for codes again.

nbanwart

With the key in the run position there is no check engine light. All of the wires running directly from the battery to the main wiring harness have a confirmed 12v going through them. Where is the ECM fuse? Is it in the fuse panel or elsewhere, as I did not see one in the fuse box in the car.

RBob

iTrader: (1)

At the ECM, the white connector, pins 10 & 15 get battery power through a fusible link. The wires are orange.

Pin 16 gets +12 V via the ignition switch. It runs through a 3A fuse that is likely in the fuse block. It should be labeled "ECM IGN", second row from bottom, center of row.

RBob.

nbanwart

Ok, the ECM IGN is good. Just checked all terminals on the white ecm connector, nothing over .5V with most being at 0V. Is there anything after the fusible link from the battery but before the ecm that would cause there to be no power? I don't think the wire is grounding out somewhere in the bowels of the car the battery is not losing charge.

RBob

iTrader: (1)

There is a splice in the orange wire, likely under the hood. Once it leaves the fusible link as the orange wire it goes to the oil pressure switch (fuel pump relay backup), the fuel pump relay, and to the ECM.

I would check for +12 V at the orange wire in the fuel pump relay socket and the oil pressure switch connector. It may be that the splice is bad, but I'm not sure where it is located.

RBob.

nbanwart

At the orange wire in the fuel pump relay, the wire is reading 12V. Have not checked the oil sender unit's voltage, however, I found this relay with the 3 left and 2 right wires touching each other near the windshield wiper motor and brake booster. I'm cleaning it up as we speak, but do you think this might have something to do with the problem?

RBob

iTrader: (1)

A rhetorical question?

RBob.

nbanwart

No sir! I was wondering if the circuit it was connected too was irrelevant to the ECM or anything like that.

RBob

iTrader: (1)

It appears to be the fuel pump relay connector. It has the correct wire colors and splices for it to be. From the left:

Double reds, A: one goes to oil pressure switch, the other goes to the ECM monitor and to the fuel pump fuse. From the fuse it goes on to the pump.

Blk/Wht, B: ground for the coil

Grn/Wht, C: +12 V from ECM to activate the relay

Red, D: pin G on ALDL connector, allows running of pump by placing +12V on that pin

Orange, E: +12V from the fusible link

Note that this orange wire is the same wire that feeds battery power to the ECM. Although it is via a splice off of that wire.

RBob.

nbanwart

Cleaned up and put insulation around the wires and it did not make a difference. The orange wire that goes to the fusible link has 12v, everything else has 0 which makes sense based on your information. The only place that orange wire goes before the ECM is the oil pressure gauge, right?

RBob

iTrader: (1)

> The only place that orange wire goes before the ECM is the oil pressure gauge, right?

Not exactly. There is a splice in the harness where the orange wire becomes several orange wires. It isn't daisy chained, it is a star configuration.

RBob.

nbanwart

I looked through the wiring very precisely today and could not find the issue. Would it be acceptable to rig the ecm to a ign-on power source? And if yes, how should I go about doing it?

And thanks for your help so far RBob

Dominic Sorresso

That's exactly what my connector looked like when I noticed it working on an oil pan gasket. Don't know how I avoided having a major short and possible fire for all that time. Every once in a while my motor would hiccup. Then I found that.

kauboy

Follow RBob's advice, trace and repair the orange wire and it should be fixed.

Challis0

Guy's i would like to share something Do you hear the fuel pump prime with key on engine off. Check all the fuses. If the fuses are good get a schematic and check power and ground to the ecm. If you have a spare distributor you could try one...........

nbanwart

Well, just for fun I put 12v to the 10 and 15 pins on the ecm...and nothing. No check engine light, or anything of the sort. Does this mean the ecm is completely fried? I thought that the car would throw a code if the computer was done for. Where is the ground on the computer?

RBob

iTrader: (1)

The ECM gets ground via the harness to the engine block. Look for black/white wires in the harness. Such as found on white 12 & 13.



RBob.

kauboy

Wouldn't hurt to check the bulb. I've seen some systems where if the check engine light bulb is removed, it goes into a "limp" mode. It is a possibility the ecm fried and blew the fusible link, but check all your power and ground to the ecm before you condemn it.

nbanwart

I have both power and ground to the ecm unfortunately. If it went into a 'limp' mode, it would probably less severe than total shutdown, wouldn't it? Also, would I need to replace the prom as well, or would it be fine if I took the old one off my current ecm and put it on the new one?