Builds Boost and then Nose Dives

[91Bird305]

Have a strange issue and some clues that might spark why it's happening (maybe?).

First off, no I don't have a PL but I am getting one (mainly for reasons like this).

What happens is this, I will get into the boost, usually anywhere after 10lbs but it can be anywhere from 10-15lbs and the car acts like it cuts out. Car lifts, builds boost fine, then it acts like everything just cuts out and the SES light flashes real fast when it happens and then nothing, car drives fine.

What do you think? Possibly short somewhere when the car lifts? Or something else? I just find it odd that it feels like the whole car shuts off for a second and the SES light blips when it happens.

I don't have any codes though. So it makes me wonder if it blips because the car loses power for a second when it happens.

I am going to trace my battery cables to make sure there isn't an issue there, and yes they're tightened down on the battery.

Just find it odd that it's completely random boost after a certain amount. Like something is sliding and cutting the power and then sliding forward when the car nose dives.

Your thoughts are appreciated, as always. If you have questions, just yell and I can find them out.

 

[Blazer406]

I'd suspect one of these:

1.) Ignition module/coilpack
2.) spark plug gap too big...
3.) battery cable shorting out under boost.... usually under the pass header....

HTH

 

[Clark6]

I'd suspect one of these:

1.) Ignition module/coilpack
2.) spark plug gap too big...
3.) battery cable shorting out under boost.... usually under the pass header....

HTH

I could be wrong but i vote for #1.

 

[91Bird305]

The ignition module is brand new.

Anyway to check the coil pack?

 

[Blazer406]

The ignition module is brand new.

Anyway to check the coil pack?

All ignition modules are not created equal.....

Is yours a new AC Delco?

Non-AC Delco modules usually will not test on a Caspers ignition module tester.... that ought to tell you something...

Even AC Delco...isn't a gurantee that it will work properly.... but your chances of success is probably 10 fold...

 

[Rafs-T-Type]

All ignition modules are not created equal.....

Is yours a new AC Delco?

Non-AC Delco modules usually will not test on a Caspers ignition module tester.... that ought to tell you something...

Even AC Delco...isn't a gurantee that it will work properly.... but your chances of success is probably 10 fold...

i had a no-start condition and thought it might be the ignition mod so i replaced it...that didnt work so tried other stuff...sure enough it was a faulty new ignition mod...i was pissed --o yeah...it was ac delco

 

[91Bird305]

Any way to check other then replacing it?

 

[Clark6]

The ignition module is brand new.

Anyway to check the coil pack?

swap one off a friends car, 10 minute job to swap the whole thing.

I got one new off a early 90's cutlass that was new(borg warner) .. worked fine.
bought one used with the module and coil pack on off an 87 Riviera for $20 off ebay for both. worked perfect, ran a 10.75.
I was trying to chase other problems so i have them as a spare.
Any way just to rule it out....


You can check the resistance between each towers with an ohm meter should be 11k-13k ohms between ea. If this helps could be weak coils though then that test wouldnt work i dont think...

 

[91Bird305]

Cool thanks. I don't know anyone with a spare ignition module but we do have a multimeter so I will use that.

 

[Rodney87GN]

I just find it odd that it feels like the whole car shuts off for a second and the SES light blips when it happens.

I don't have any codes though. So it makes me wonder if it blips because the car loses power for a second when it happens.

IMHO, I think you're on the right track about the ECM losing power. Did you check the orange ECM wire by the battery? With the car idling jiggle the wire around and see if you can duplicate the problem.

If there's a break somewhere in that wire, the smallest vibration can undo the connection and cause those blips....same thing happened to me.

Just a thought...

 

[Blazer406]

IMHO, I think you're on the right track about the ECM losing power. Did you check the orange ECM wire by the battery? With the car idling jiggle the wire around and see if you can duplicate the problem.

If there's a break somewhere in that wire, the smallest vibration can undo the connection and cause those blips....same thing happened to me.

Just a thought...

That is why I posted # 3 in my first post above.......... cause it happened to me..... took forever to figure out. I had a broken drivers side engine mount.... and it let the engine rock over during hard acceleration.... enough so the battery cable going to the starter.....contacted the bottom of the hot header...and eventually shorted killing all power.....on the sudden loss of power...engine would rock back the other way...and unshort itself...... all this would only take about 2-3 frames on my DS which was shooting 18 frames per second..... so it was nearly instantly it happened and was over...

I've seen this happen to several cars.

Keep us posted...

 

[91Bird305]

So I started by checking my positive cable and first trace it to the alternator where I have my hotwire kit. During that tracing process, I noticed my reservoir tank that holds my meth had a small leak where the "low" sensor is located. So I had to take that out. I don't know if I have to replace that sensor or if that will even fix my leak issue.

Anyways, after that I tried tracing it down to the starter but had trouble seeing where it went without removing the headers. So I tried to simulate what might happen when I put load on the car on the street by moving the battery a bit and that's when I heard the car lose power on and off. So I know it is related to the battery (at least I think I found it).

Anyways, so as I am doing that, we decided to test it out and I would start the car while my friend move the battery a bit. Oops, car won't start. Fuel pump won't kick on now.

Started testing the connections with the fuel pump. It is getting power to the pump, but the wire that runs from the ECM / ignition is not sending any power to the pump to tell it to turn on when I have the key in the on position. So I am trying to trace that gremlin now. No idea how that happened.

So that's where I'm at right now. I believe I might have found the issue, but then ran into 2 problems hunting for it. Oh well. I love cars so much.

Anyone have a diagram of the back of the ECM on a 87 GN? I need to find out where that grey wire begins that tells the fuel pump when I have the key in the on position. Maybe I'll make a separate thread for that.

 

[3.8L V-8 eater]

That is why I posted # 3 in my first post above.......... cause it happened to me..... took forever to figure out. I had a broken drivers side engine mount.... and it let the engine rock over during hard acceleration.... enough so the battery cable going to the starter.....contacted the bottom of the hot header...and eventually shorted killing all power.....on the sudden loss of power...engine would rock back the other way...and unshort itself...... all this would only take about 2-3 frames on my DS which was shooting 18 frames per second..... so it was nearly instantly it happened and was over...

I've seen this happen to several cars.

Keep us posted...

Had the exact same thing years ago on my 86' Gn. Battery cable came loose from the clip that holds it to the frame.

 

[Sleeper-6]

Sounds like you found the source your problem, No you just need to find out what it is. When you turn the key on, without starting the car does the "Check engine" light turn on solid? If so, you know that the ECM is getting power.
If not, I would give your battery cablkes a real good check, both power and ground. Check for power at the orange connector near the battery that powers the ECM.
Might as well check the fusebox while you are at it. Cheap and simple first is a good way to troubleshoot things.

 

[91Bird305]

Just a quick FYI about the fuel pump not kicking on from the ECM. You were right. That SES light is not coming on when the key is turned into the ON position and the scanmaster is only showing the version and going blank. I think the power to the ECM is dead. Going to do some more testing and find out where exactly. I have 2 orange wires that come off the ECM and into a connector that looks like comes off the alternator? Have to do some more wire tracing to be sure.

 

[Rodney87GN]

The orange ECM wire mentioned earlier branches off the positive battery cable lug. It's a short piece of 14 gauge red wire that goes into a fusible link and out to an orange wire that goes directly to the ECM. It has a weatherpack connector right after the fusible link so you can disconnect it to reset the ecm.

When I first bought my car that orange wire was taped to the AC condenser hard line to hold it in place...that was the "sweet spot" so as not to disturb the connection to the ecm. Previous owner was having the same problem as you!

 

[91Bird305]

Just a quick update, the ECM wire from the weather pack by the battery to the alternator had a bad connection somewhere in between there. So I reran that wire and the ECM has power again, but the fuel pump still won't prime. Checked the wire from the ECM and it is putting out 12 volts to the pump for like the first 2-3 seconds when the key is turned to the ON position like it should. Ruling out the bad ECM theory. But the wire going to the pump is getting no juice. So instead of trying to find that wire in the engine bay, I am just rerunning the line. Just faster that way right now then trying to retrace everything in the engine bay, back to the pump.

Should have that finished tomorrow. Stopped around 9 to watch the Office and Southland.

Let you know what happens tomorrow.

 

[1quick6]

My fuel pump was doing the exact same thing. It would prime and pump for about 5 seconds before the pump would lose power and kill the car. It ended up being a bad fuel pump relay.

 

[91Bird305]

Mine is doing the exact opposite and not priming. The voltage to the wire that sends the signal for it to prime is 0 at the pump, but 12 volts at the back of the ECM. The relay is working correctly, it just isn't getting any juice before the relay or at the pump.

Instead of winding through dozens of green/white wires to figure out which is which, it just seemed much easier to just rerun my own wire.

 

[1quick6]

Oh, before the relay. I should have had some coffee before replying. haha