ULTM8Z

So what's the significance of run time on electronic spark timing monitoring?

My code 42 came back last weekend, so I've been running an experiment. When I had this in the past, it always seemed that the SES light would come on after about twenty minutes to a half-hour of driving. So I drove the car three times for that amount of time while keeping an eye on the scanner set to display engine run time. Turns out that each time, the SES light came on between 1800 and 1805 seconds (a half-hour). The elapsed time is independent of freeway or street driving.

This isn't a coincidence. What's in the 8D code that would cause it to detect a spark timing monitor errror after exactly a half-hour?

ULTM8Z

Ok, my GM Port Fuel Injection manual has a code 42 troubleshooting test that I just reran.

One of the tests is to disconnect the ECM, turn on the ignition, and check resistance of circuit 423 (white wire to module) to ground (one DVM probe on white wire terminal and the other probe to ground). It's supposed to be less than 500 ohms according to the test. The aftermarket module I have on teh car shows 520. Putting in a GM module, the reading goes down to 352. I had run that GM module in the distant past, but it would give me a no-start from time to time so I took it out. Maybe I need to get another GM unit... A couple of aftermarket ones that I have had resistances of 538 and 830 ohms.

Anyway, does someone have their 7730 ECM handy to check this circuit on their car and see what the value is?


Here's a very basic question: Do I need to run a Vette ECM with a Vette distributor? I'm running a 7730 with an ANHT as the baseline, but is there something peculiar about the Vette ECM that would make a 7730 incompatible with large cap Vette distributor?

DENN_SHAH

iTrader: (1)

my books are saying it should read less than 1000 ohms for both systems. i looked it up for a 90 & 91 vette, 90~92 camaro.
have you tested ckt 424?

strange that it sets like that.
maybe its the module getting hot & breaking down & it just takes it that long to get bad enough to fail the test.

i have had tons of problems with code 42 caused by after market modules.
in some of the classes i took i was told that they left some of the circuitry out to lower the price.
the aftermarket modules can cause all kinds of run problems.
besides code 42, i have seen intermittent misfire, surging, intermittent no starts, low performance, bad fuel mileage, short module life, & pinging, all caused by the after market modules.
once i convinced my boss to stop using the after market ignition parts, almost all of those problems went away. it seemed like maybe 1 out of 3 was good.
also, if i replace the module, i always replace the ignition coil too.

ULTM8Z

Ckt 424 test is simply to connect a light to 424 and to 12V. Light is on when I do that test. If light is on, I'm supposed to disconnect the 4-wire connector at the distributor. When I do that, the light goes out. At which point, the flow chart tells me that the module is bad.

Now, I was under the impression that a bad module would not allow the car to start at all. Is that not the case? Sounds like you're saying that a whole host of driveability problems can be associated with a faulty module. Now I need to go buy yet another module... In which case, I'm getting a GM one.

jwscab

I can definitely relate to using GM modules whenever possible.

Short story, my 87 iroc crapped out one day, after driving for about 45 minutes, then shutting off(parked). few hours later, crank and crank and crank, and nothing. Starting changing parts, including the module. after changing it to an aftermarket, i got it started, but the thing would stall once you put it into drive. When I changed it, I noticed a ton of oxidation on the pickup terminals, and the connector just melted apart. so I cleaned it all up. So after probably a few weeks, I got frustrated and put the original module back in. Ran awesome! So curious what the deal was, I threw the module on my test bench, and compared it to a GM module. timing was all over the place below 600 rpm or so, which means, whenever I would put the car into drive, the rpm would dip, the module timing was all over, and the ecm couldn't counteract, thus stalling. expensive lesson, as I replace alot of sensors, but at least the engine is like 'new'. Also pointed out the fact that the corrosion was the real culprit.

I would guess something like an MSD module would also be OK, but I can't prove it. regular 'replacement' parts should be avoided though.

ULTM8Z

Well, I just ran my sensor tester on all the modules and they all pass.

So it has to be a heat related issue. Though I'm still confused by the consistent timing of the SES light coming on.

jwscab

you could always buy a cheapie temp thermocouple and wire it into the distributor, you can mount it underneath, where the module 'sinks' into the dist. base, then see if the CEL and a specific temp correlate. It might take awhile to build temp to the point where it's faulty, if thats the case, it might be pretty repeatable, and the reason you see it happening at around the same time each test.