coltonstewart

My engine runs like crap, wont idle. 3.0 92 pickup. Ive run through nearly every troubleshooting possible.. Im doing ECM tests out of the FSM - http://htftp.offroadsz.com/marinhake...E/102engin.pdf

The directions say "Dicsonnect the connectors from the engine control module (ECM)." so really its not the ECM you are testing, its the electronics and the wiring for the whole truck. I have run across some typos before so i just wanted to clear this up, and ask if this is the correct way to perform these tests. Maybe i misinterpreted something who knows..

My problem is that at one step it says to disconnect the VAFM and then measure the resistance between THA and E2, which is supposed to = 2-3 Kohms. Well, if you look at the wiring diagram ( http://www.snjschmidt.com/wiring/Eng...rol_3vze_2.jpg ) of THA to the VAFM, THA makes no contact with any other sensors or splices..... so logically THA - E2 should = infinity with the VAFM disconnected. This is what mine reads. I dont know if this is a problem or not.. CAN ANYONE EXPLAIN HOW THERE SHOULD BE 2- 3 K?

My other issue is that VTA - E2 w/ throttle valve open should = 3.1 - 12 k omhs, and mine = 1.3 k. However when i measure the resistance directly at the TPS, VTA - E2 w/ throttle valve open = 4.3 k ohms (which is within spec). This is another wire that only goes directly to the sensor.

Maybe my wiring is bad? Maybe im missing something? Help guys i know yall know some s#!+

coltonstewart

Also, my Voltage value for VTA - E2 (throttle valve open) = 2.5mV and it should be = 0.3 - 0.5 V. Yet again another wire that isnt spliced just goes straight to the TPS

wyoming9

iTrader: (1)

First 2.5 mV is the same as .025V

All the schematics your using are for the 1992 Pick Up??

If your checking the ECU some tests your checking the harness side others your checking the ECU side

With the AFM disconnected your measuring the harness side of THA to E2 not the AFM side

You have ruled out head gaskets ??

Just what do you mean idles like crap ?? That can mean many different things .

Starts spits and sputters and quits

starts then just quits

starts idles up to 3000 rpm and stays there

idle cycles from 950 rpm to 2500 rpm for no real reason

At any time did the CEL come on and what were the codes if any??

What other steps did you take ??

Is this a case of rodents chewing wires or the ECU getting soaked with water

rustypigeon

For the first issue, that is an error in the FSM. They have the "condition" flip flopped for values VC-E2 and THA-E2. It should read as follows...

Terminals / Condition / Resistance (kohm)
VC-E2 (E21 ) / Volume Air Flow Meter connector disconneted / 3.9-9.0
THA-E2 (E21) / Intake air temperature 20C (68F) / 2-3

For the second issue, I would check it again. You should never be showing more resistance when you have less resistance in series, which is basically what you posted. Did you have the ECM connector disconnected from the ECM during that test? (as it should be with all resistance tests)

I would check it again at the TPS. With the throttle plate fully closed, it should read .47k-6.1k at VTA-E2 (E21). Then move the throttle plate fully open and watch the resistance smoothy rise to a peak of 3.1k-12.1k when the throttle plate is fully open. Do the same at the ECM connector with it disconnected from the ECM. Have a helper move the throttle plate while you watch the resistance values. The values you get at the TPS should be very close to the values at the ECM connector, the only difference being the very slight resistance of the wiring between the two.

rustypigeon

VTA-E2 should be 3.2v-4.9v with the throttle open. It should be .3v-.8v with the throttle closed. Are you really only getting 0.0025 volts? Many multimeters will show that tiny reading when the leads are not connected to anything at all.

coltonstewart

You were right about the 2.5mV reading being an error, upon rechecking i found the value to be .5V, within spec.

When i rechecked the VTA - E2 /w TV open, I still get 1.3K ohms. and 550 ohms /w TV closed. Whats worse is when I watch the resistance change while slowly opening the throttle valve, it smoothly goes up from 550 ohms to 1.6k at about 3/4 open, and then graduates back down to 1.3k at full open throttle. When I do this test straight from the TPS, I get good readings from 550 ohms smooth all the way to 4K at full throttle. This is some wierd stuff right?!

Thanks for the info about the FSM error. VC - E2 /w VAFM disconnected = 5.6k ohms so this is within spec (3.9 - 9.0k). The Air temp sensor not lookin so good though: at 55 degrees (F), THA - E2 is about 1.55 K ohms. Which according to the FSM bit on VAFM specs ( http://htftp.offroadsz.com/marinhake...92volumeai.pdf ) would be telling the ECM that the temp is about 100 degrees...

Im going to open the lid to that VAFM today so i can finish all my specs checks. Im wondering if that VTA wire is shorting on something, but I know its not shorted to E2 or to ground or any of the other pins on the VAFM and TPS cables. Also i checked for continuity between the ECU and the TPS and VAFM and everything seems solid.

Basically its running rich, sounds like its firing half the cylinders, wont idle without throttle, and now and then it backfires or predetonates into the intake. It isnt throwing any trouble codes.(although it did have a knock sensor issue that I fixed with a new sensor and dedicated leads to ECU and shielding to ground. but i dont see how this could affect anything else leaving the old ground/shielding (E1) clipped and electrical taped at the knock sensor harness connector)

coltonstewart

Sorry to resurrect a dead thread but for posterity I thought I would add (despite the embarrassment) that the reason for these symptoms was caused by me forgetting to install o-rings on the ceramic fuel injector seats. Yeah..