After the rollover my '91 did this. At the time I was working for a company developing a medical instrument so we had all kinds of scopes and digital analyzers. Real high end stuff and the folks who knew how to operate it.

I'd already gone down the path of 'replace this, replace that' using a friendly local bone yard. No help there.

So we hooked up a digital HP scope and watched the lines. Sure enough the computer would just shut down for no apparent reason.

Symptoms just like you describe, a big lurch, tach to zero, flash the cel, but no codes would get trapped by the computer.

We never did find the cause and it was still doing it when I got rid of the truck.
Only good news is that it's not a show stopper, it'd lurch and keep right on running. Never did quit.


Only suggestion I can offer is to try beefing up the ground straps.

If you ever find it, be sure to post it here, I'm still curious.

 

[QUOTE=MonsterMaxx;50359626]

So we hooked up a digital HP scope and watched the lines. Sure enough the computer would just shut down for no apparent reason.

Symptoms just like you describe, a big lurch, tach to zero, flash the cel, but no codes would get trapped by the computer.

QUOTE]

Thought if the CEL flashes, it should store a code. But if the ECU drops power momentarily, it would not store that... makes sense.

Btw, in case I ever need to do it, I've a very good Tektronix scope I use for other purposes. How hard is it to get at the ECU leads?

 

Could it be the efi relay going bad?

 

*hears crickets*

Well, I am going to pull the ISR mod off tonight and put the stock intake back on.

 

Wow sounds just like my sypmtoms. We found the ECU was burned or had some noticable charring. We had it repaired. Ran it, it ran fine then jerked again. We pulled ECU to find charring again. We have ordered another used ECU and resent the original for repair.

What did your scope show? Was it a power issue into the ECU that died or was it internal power?

JJ

 

FROM MY POINT OF VIEW IT SOUNDS LIKE YOUVE ALMOSRT FOUND YOUR PROB....
IF IT WAS MINE...
1.)i'D CHECK ALL FUSES AND RELAYS...
2.)SEE WHAT KIND OF SHAPE MY WIRING IS IN GOING TO THE ECU
3.)FIND A DONOR ECU FROM THE JUNKYARD
A.)Get a new/rebuilt one if the donor fixed the prob

From what your saying, the ECU is definatly losing power...SO.... that should give you a area of focus.

 

sounds to me like you have a current carrying wire leaving the ECU that is exposed and touching ground. OR you have somethign that lost a ground and is trying to find ground through a wire/trace in the ecu, thus pulling a LOT of current through nad burning up the traces...

Tracing down such a beast is going to be one of the biggest pains in the ass I think one will EVER encouter in a vehicel....

 

1. All good. And checked with a digital multimeter and my FSM.

2. Suspect, as the Engine Wire is pretty brittle, and make have broken some wire(s) when I yanked the motor. I have e-mailed my Parts guy to see how much a new Engine Wire will cost.

3. I have a spare ECU. I am also looking for the connectors to make a MegaSquirt adapter.

 

SPare ECU is from a 92/93.

will this work for my 91???

 

Update 1/11/2007

Scott, a buddy of mine who is also a Toyota Master Tech suggested that I do a few different things this evening.
He told me to check the vacuum at idle, as well as to check that each cylinder is firing.

Vacuum is 14.5in HG at idle

I pulled the spark plug wires one by one.
That coil puts out a serious jolt!
ANyhow, pulling the plug on number 3 cylinder didn't make a difference in engine speed.

I think that may be my culprit.
IIRC that was the problem cylinder before, and I had actually disconnected the injector plug so it wasn't spraying fuel. THat might have damaged the wiring.

I am going to try to dig into it tomorrow afternoon.

 

1/14/07

Checked the spark plug on number 3 cylinder
It was not fouled, and looked to be in great shape.
IT didn't smell of gas or exhaust.
So the cylinder wasn't getting fuel.
Pulled the intake apart, and tested all teh fuel injectors
Inj 1,2,4,5,6 all read 13.9-14.1 ohms

Inj 3 read open.
Replaced it this evening, and buttoned it back up.

Drives much nicer now.

 

Mine stumbled randomly when the alternator was gone (I think it was the voltage reg specifically) but it was obviously the alternator because it would drive fine then the lights would fade, engine stumbled, then back as if nothing had happened. Did the alternator, no probs since. I can't see one plug dropping your revs to zip... but I'm no mechanic either.

 

hahahaahah Im glad im not the only who has been popped by the coil!! LOL I got nailed at least a half dozen times too...lol

congrads on getting the stumble worked out!

 

Sorry I didnt read the whole thread so if you tried this already sorry. I got my AFM off ebay, it waslike 40 shipped so if thats what you need watch ebay. Mine got rusted shut, was in water over the hood and when I got out I never dried it and rusted the flapper shut, was running richer then a duramax with a bullydog system on it lol.

 

my truck is doing the exact same thing....i cant figure it out either any suggestions

 

look up 4 posts and you will se his answer to what his problem was

 

Well my stumble is back. I had thought a new ECU would do it, but NOPE!

I get a random jerk / stumble very rarely. I ran butane around all the vacuum lines and intakes to check for a vacuum leak...nothing. All wiring looks good. I've kinda stopped looking for it, but it does not instill confidence.

JJ

 

A new wiring harness from the dealer is pretty expensive.
Shannon at Champion Toyota in Houston is supposed to be a good contact to order dealer parts at a significant savings. Sorry, you'll have to google the dealer for a website or phone #.

 

i should know better than to play in a graveyard, but read through and remember this problem on a few different cars, lost my damn shirt on the first one, warranty diag too... car would cut out randomly, but never quite stall.. check eng light comes on for a second, then light goes out, car catches itself, and drives completely fine besides that. no DTC's either. anyway, found intermittent power loss to ECU, ended up using an oscilloscope on very high frequency across the battery terminals, and took about 2 minutes of staring without blinking to catch one tiny little spike as the engine cut out, voltage would shoot up, and as it did the car would cut off. the voltage regulator in the alternator was going bad, started to push out 16+ volts, and the ECU was shutting itself off to prevent damage. and FYI, my fancy dancy digital volt meter never showed the voltage spike, but showed the drop to 0 every time.. hope it helps someone