Help with engine Theory & what keeps an engine running?

[Burt4x4]

SO here's the deal:
I drive my K5 for the first time on a road trip w/ the new 454 in my 72. About 55 miles each way to work.
Now my 454 has Edelbrock MPFI so it is 100% computer controled.
On the way back home (much hotter than the am trip) my engine died while goin about 60-65...just died like I turned the key off.
Pulled over,tried to start and it barley turend over so I kicked in the dual batt. switch to combine the batss and it cranked over just fine but no start, poped hood, wiggled coil wires, fuel pressure was still present, tried to start again and it STARTED!
Drive for anoter 20min and it BAM, dies agin the same way, I do the same thing and it starts agin??
10-15min later BAM dies again..flat dead no start...wait...Varrooom it starts!
I make it home.

OK so I'm thinking my starter batt (controlls allthe + connections) is droping voltage of shorts out or does something to make the MPFI trip a silly or something that can be reset by turning off the power...wait...power up and fire in the hole?
I belive the Edel. MPFI has a minimum voltage requirement, so it may be that the primmary batt kills or lowers the voltage enough to shut down the MPFI computer.
Anyway I'm gonna start by replacing the main batt, it is 6yrs old and sat fer a year. It starts my cold 454 fine but add heat and it has no power...
Thougths, Ideas???
I am drinkin beer thinkin about theory so let me know your thoughts if you have time.
Burt

 

[4xcrazy]

my 1/2 ton pick-up did this the other day, found a loose battery cable.


something so simple...

 

[Ryan B.]

Hm, weird.
How did you ground the ecm? my tpi harness had a dedicated ground for the whole harness, and i ran that through the firewall and bolted it to the rearmost intake manifold bolts. that way its seeing engine ground like it should, with a ground cable going to the frame and to the battery.
If i were you, i'd pack the digital voltmeter in your truck that way you can probe a few different points, maybe even get the leads with clips and leave it hooked to your ecm power (and tape it up so it cant short out and blow your computer) so you can see if its dropping voltage after you drive for a while and it heats up like you suspected.

Another thing, is heat increases resistance in wires. If you're using an old wire that feeds your fuseblock, and then thats where you ran the new wires from the fuseblock to your ecm, maybe the old wire from the battery to the fuseblock has a bad connection or the wire is brittle so when it heats up the resistance increases... the voltage drop becomes greater, then your computer doesn't see enough voltage and shuts it down like you were saying? i donno.. that sucks man. i hope you get it figured out.
How about checking the coil 12v wire making sure thats not loose, and ignition related stuff too?

 

[FWP]

Start with the 3 simple things- Fuel, spark, and compression. I'm guessing spark is missing. try this. Immediately after it dies, try to start it, and check for spark. My guess, there won't be any spark. Back track from there. Bad pickup coil in the distibuter, no power to ECM, Faulty ignition coil, etc etc. HTH and gives you some ideas.

 

[jekquistk5]

sounds like somethings shorting or your altenator isn't working if you have a weak battery after it dies.

 

[Burt4x4]

Cool Thanks Fellas
The ECM is powerd by a new fusebox I put in so the wires are new.Ground for the harness is to the lower part of driver's side head, the front of the head is grounded to batt #2. I do need to add a block to frame strap, I have a head to fender well ground strap on the pass side plus primary batt ground to same head.
My hand held computer for the MPFI displays voltage and in the am I was @ 14.** and on the way home in the heat I was down to 13.4 & 6.
That primary batt can only start my engine when it's cold, everytime I try to start at operating temp I have to combine the batts. I too belive I am losing all spark....were exactly??? duno. I have a new batt on order so I'm gonna start there along with a physical of my wireing job

 

[Mad-Dog]

The hot start problem has me puzzled, something (starter motor) is drawing entirely too much current when it gets hot,
1 battery should start it all the time even when it's at operating temp.

This thread has BAD GROUND and/or STARTER written all over it but you say ya got the bases covered so i dunno....

You got 2 different problems and need to isolate and fix them individually,
maybe once ya fix the starting problem the FI problem will cure itself.

 

[rjfguitar]

Sounds like you are having about as much luck as me trying to gear up for the fest. Yours dies and mine only starts when it wants too. Hope you get it worked out, I'm not good with wiring or I'd throw something in, but it probably wouldn't be right.

 

[dremu]

I think the two problems are one; yep, it sounds like no fire, but if the voltage at the FI unit is too low, I betcha it just cuts out, so you get no fire. Nothing wrong with the dizzie, pickup, coil, etc ... just the computer thinks the truck is being shut down, or goes into a safety mode or something.

Fix the battery and/or grounding first, see if it's happy.

And BTW, congrats on getting the thing running. That's a hell of a truck!

-- A

 

[rjfguitar]

I do know that Detroit ECM's shut off at 10volts. Don't know if the Edel. ECM's are the same or not.

 

[LongIslander26]

Battery?

Sounds like you have a dead cell with an intermittent short in the battery. You've got voltage but no amperage, and sometimes the battery will work fine (Usually when you're testing it) but get out on the road and that's when trouble starts. Remember, MPFI engines won't stay running if you disconnect the battery like it would with a carburetor.

 

[dyeager535]

Do you lose all power to the vehicle, or does it just shut off while the (seperate) various gauges, radio, lights etc still work?

If it's a battery issue, you should see it in the volt gauge when it occurs.

Can you real-time monitor the voltage the ECM is seeing while you are driving? If the injection is wired up similar to the stock fuse panel, then you should be able to eliminate all of that if the fuse panel stuff keeps working when the problem occurs.

I don't know what GM systems require to keep operating, but I know the injector constants are modified based on the voltage the ECM sees, on the high end to something like 25V lol, so you know voltage variations are goingt to be accounted for. If you've got 12V (as the ECM sees it) and it IS a voltage problem, you would see the drop that kills it. If it won't restart until you wiggle wires/switch batteries, then the condition that caused it to die, if voltage, should still be present, so having to monitor it while driving, unless you have a passenger and want to, shouldn't be necessary.

If it's as consistent now as it was when you were driving it, then it should be pretty easy to narrow down.

 

[chevy_muscle]

I think you're on the right track. Replace that 6-yr old battery and make sure your new battery has solid connections when hooked up.

Let us know how it behaves after that.