96 was a 5.2 and no crank codes puled with the snapon

Set fuel sync to 2

No codes have been shown sence crank sensor replaced long ago.

Going to buy a new ignition swich and replace for ****s and giggles

 

Ok, so your running OBD II that was OEM'd for a 318 but, since has been flashed to accommodate the larger displacement engine.

Since you have no codes, that means that it's receiving a 5 volt signal at the PCM input- that's all that means. I have had mine run like total junk without throwing any codes due to changing both CPS and CKPS. The timing was so far out of sync that it was backfiring like a mo fo. No codes were pulled. Just because you saw no codes doesn't necessarily mean that it's ok.

 

correct that just leaves me to look at other things also. My buddy printed up some wiring schematics and gave them to me and another buddy is an electrical engineer is coming over tonight to go through the whole wiring harness to look for anything like bad connections splices ect.

 

Good for you. Get the EE on that to rule out possible wiring fault. Check the grounds as well as for high resistance.

Good luck,

CM

 

thanks will post tonight or tomorrow

 

bad news the ee and I put in 7 hours on the truck last night and still are no closer to finding the problem.

For our tests we put two leads into the cab of the truck and drove it to get the condition to repeat itself and watched either a test light or multimeter to deternime if connecion was good or bad.

Both Power to the back side of the pcm connector is good.

Ground to the back side of the pcm connector is good.

Coil is cutting out.

ASD relay is being opened and closed by the pcm. Some times but not all of the time. So this seems to be a by product but not the cause of engine shutdown.

Crank sensor was replaced.

Cam sensor was tested and all is good.

Fuel sync is 2.

No fault codes

Has a remote start that quit working a month ago about when the problem started. Will try to yank it out today.

Some thoughts. The snapon tool when driving said that it was losing sync signal to the pcm. But we only tested to the back side of the connector not through the connector. I dont know how you would aside form sticking a very tiny wire in there and closing the connector. Test light could have blinked soo fast that it seemed to stay lit when testing ASD. need a data loger.

Any thoughts I leave for texas in a week.

 

When power is cut to the ASD relay off that main supply line, all power is cut to the entire EFI system. This includes the coil, injectors, and fuel pump. What type of light were you using to verify your ASD power? By using an LED lamp, it's much easier to spot a drop vs. the old, bulb type. FYI

Regarding testing that connector, never put a thin wire into a connector-ever. He did it correctly by backprobing it and, what comes in on one side has to come out the other. You test it on both sides. This verifies both sides. At any connector, you have a pin on one side to a pin on the other side. So, what comes in must also be seen on the opposite side. You never want to stick anything inside due to it moving around and shorting / sending high power / current to a low power circuit thus frying it. In the case of a connector such as at a PCM, the connection can be tested for resistance by simply removing the connector and testing the pin for high resistance. Should read near zero ohms (remember to account for test lead resistance) Usually, these connections remain intact for a very long time without oxidizing.

Now, what also may be happening is that your having an issue with the power module to the logic module. Did he verify that voltage to the PCM is constant under use?

When you tested the ASD relay, did you or did you not verify the OHM reading first across the pins in both powered and UN-powered? There could be high resistance at the input side of the ASD relay thus causing a voltage drop thus causing the coil to disconnect thus killing power. Check your ASD relay first. Then, once you've verified it is working correctly and to spec, move on to checking the feed TO the ASD. Verify that you've got ~13.58 volts first. Then, check that wire for high resistance. You will have to open up the PDC to do this. Check for cuts, shorts where the harness enters the side of the PDC. It has a habit of chowing into the wires due to the sharp plastic edges.

Once those have been tested good, now, check the feed to the coil from the ASD relay. Check it for high resistance and continuity. While you've got the meter on it, shake the harness along the length up to the splice out where it ties into the cowl. If it drops out, there's your issue.

That's the engine half of that circuit. Now, what you need to verify is the PCM side. There's two sides, power and PCM. There's a line coming from the PCM to the ASD relay. This is how the PCM shuts the ASD relay off. It opens that, it kills power. Trace it out from the PCM connector all the way to the PDC. Remove the connector from the PCM, use a paper clip attached to the probe, then trace it out across the harness to the PDC. Check for high resistance / open.

Did you check grounds at both chassis, ALT and the body grounds for the PCM?

The remote starter must tie into the main feed line. It may be an intermittent connection that's causing the main supply feed to go open. I would crawl under the dash and see what's going on with that. Check the connections there.

 

by using an led test light we conferned that the pcm is always getting power even when the glich happens. With the light tho we did not determine how much power.

all grounds seem good

we tested the asd relay and all seemed good wit it. But will do more checking.

Only happens when driving and after the motor is warm. The warmer it gets the worse it gets.

Can sit in the drive in park or nutral and hold her at 2500 rpm all day long and it wont glich only while driving.

 

You can simply test how much voltage by removing the connector and measuring the voltage. But, there's a tolerance for the voltage and, if it's not enough, it shuts down or, you get erratic behavior due to a low voltage condition. But, if the main supply line / feed to the PCM checks out fine, and the voltage is correct at the starting point, (source) that's not the problem.

I would bring it in and have a DRB III scan tool run on it. Now that you know it's not a drop out in voltage condition to the PCM, you can rule that out and start looking into why the PCM is cutting the ASD relay out.

The PCM will always have power no matter what. This is what keeps the NVRAM active at all times. So, if your not losing power there, you may have an issue either due to a sensor fault that's triggering the shut down command (sporadically) or, you've got a supply/source issue to the ASD relay. Most of the time, it's not a source (B+) issue but, rather a ground fault issue.

Bring it in and run a DRB III full diagnostic, electrical scan for 200.00 bucks. They will go through everything. Did you check your fuel relay too? That's also on the same circuit as the ASD if memory serves me correct. How about fuel pump amperage draw? Did you test for that as well? That's another one that I believe will trigger a shut down command. If it senses high current draw on the pump circuit, it cuts power to prevent fuel pump motor burnout.

Speaking of fuel, how's your fuel pressure? IF the PCM detects a low pressure condition, it will cut power to the ASD relay. What injectors are you running on that 408? Do you have the correct lbs/hr rating? That would also contribute to why it's not running right. If the flow rate is not correct, the PCM will trip a shut down command due to insufficient fuel. Same thing happens when the fuel pump circuit has high resistance, or, the regulator is going out or, the pump motor is going out, all contribute to insufficient fuel. Now, with a low output, you can measure that and find that as well as high resistance in the lines however, if the flow rate at the injectors is rated below what should be in there for that size displacement, the pressure shows fine but, your not getting the proper fuel ratio and, if it's severe enough, it will trip the shut down command.

There was also a motion sensor that will also cause a shutdown on some vehicles. That one I can't recall as it's not that common, but, if my memory serves me correct, the sensor is used to detect a sudden stop motion that triggers the shutdown command at the time of a sudden impact.

One other thing, there's a neutral safety switch. I haven't looked into the schematics to see how this fits into the wiring scheme, but, you may also want to check that one as well. Some use a brake safety switch that also ties into the ignition.

Again, bring it in, run a full scan and they will find your problem quick- unless, it's a ground fault issue in which, they will have to trace it out.

 

fuel pressure was 45-50 a couple of months ago. running 24lbs. injectors . thanks for all the info. Need to keep working on your suggested items. Yeah and my luck I guarantee it will be a ground fault and I will be out 200 and they will say sol. or pay us to dink with it.