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Jerry Newton
Jerry Newton, Chevy Technician
Category: Chevy
Satisfied Customers: 4508
Experience:  ASE Master Technician, L1, Master GM Technician. Over 20 years of bumper to bumper GM experience.
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Chevy 350 eng van: Gm ckp pulse from sensor when

Customer Question

Gm ckp pulse from sensor when installed....sensor operates fine outside inserting it in the hole causes it to magnetically turn on...reluctor wheel visible thru hole and does turn with crankshaft...multiple ckp sensors operate same....what is wrong?
Submitted: 2 years ago.
Category: Chevy
Customer: replied 2 years ago.
All other sensors cmp output verified....coil and ign module replaced and checked....distributor cap rotor checked ok...if u fake the signal by quickly running metal infront of ckp sensor and giving computer pulses, comouter actually fires a plug...
Expert:  Jerry Newton replied 2 years ago.
Have you verified that there is no activity on that wire, using a lab scope or other means?
Expert:  Jerry Newton replied 2 years ago.
Wiring issues are common on this circuit, the wiring is susceptible to damage if it's not routed past the exhaust manifold correctly, and wires also break inside the insulation at the connector itself, and can result in a situation where "it works when I hold it in my hand, but when I attach it to the engine, it stops working." What you're describing doesn't make logical sense, so I immediately think of a wiring issue or a wire that's broken inside the insulation, very common problems. I would go so far as to replace the pigtail connector that goes to the CKP sensor.
Customer: replied 2 years ago.
Made a external circuit on a ckp sensor with a battery and test light....again, sensor works outside car....insert and install in ckp hole and crank flashing....test light on solid....not even conne ted to car....reluctor wheel in engine has no effect on sensor....
Customer: replied 2 years ago.
Looks like engine needs taken apart....???
Customer: replied 2 years ago.
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Expert:  Jerry Newton replied 2 years ago.
It's just not even logical to take the engine apart. The reluctor is there and it's moving, what will be gained from disassembling the engine? It seems much more likely that the electrical circuit is going open when you plug it in. I would absolutely eliminate that possibility first before disassembling anything. That connector has been plugged into that sensor for many, many miles, and experienced many stresses. It's completely feasible that when it's flexed in exactly that direction, the circuit opens, but when you unplug it and flex it in your hand, it makes the connection again inside the insulation. If this were in my shop, I'd make that wiring go away and eliminate that as a possibility before taking anything else apart. Don't overthink it, there's nothing inside the engine that can be causing this, if the reluctor is there and moving.
Customer: replied 2 years ago.
I dont claim to hav the answer here, but we kept fooling around with the local circuit we built till we got the sensor to recognize the took taking the sensor out of the holder and reorienting it at a 45 degree angle...this was the only sensor we did this with as the other two behaved the pulsing. This reorientation caused the test light to flash on cranking...then we removed the local circuit lines and plugged in the harness....viola! Measurement of the output signal of the ckp sensor still bugs me tho....the output at the sensor is about .4v. The input is a healthy 11.5v and the computer ground is good....why is the sensor output so low?
Expert:  Jerry Newton replied 2 years ago.
A 45 degree angle.... do you have the timing cover removed? How are you getting the sensor at a 45 degree angle to the reluctor? I want to make sure I have this straight. You have a sensor in hand, with completely new separate circuits for purposes of bench testing, and you can't get it to generate a signal unless you hold it at 45 degrees?
Customer: replied 2 years ago.
Nothing is removed....we took the sensor out of the retainer clip and rotated it....90 deg did nothing ...45 got it to operate....local circuit first, then it did run the car...we stopped at that goin to measure the clearance between the sensor tip and reluctor wing next...with impression material or putty...will inform....never seen anything like this
Customer: replied 2 years ago.
Second issue.....shouldnt the output pulse be at or near 5v on this device?
Expert:  Jerry Newton replied 2 years ago.
That's a good question, I have been trying to find a waveform specific to these engines, and haven't come up with one yet. I'll have to look at my Verus and see if they have a sample waveform.... I can't say I've ever paid attention to the voltage on the waveform, if it's there, the computer sees it and the engine runs. What is the back story on this truck? Was the front cover removed or some other engine work done to it? It couldn't have just started doing this one day for no apparent reason.
Customer: replied 2 years ago.
I use the car for hamfests exclusively which are ham radio flea markets.....its a 97 and has 150k sits for long durations then makes huge trips on wknds....had it since 99...came from georgia (im in cleveland) with about major engine problems, but have had multiple ckp sensor replacements that were successful and relatively uneventful....
I drove from cleveland to cincinnati on saturday which is about 350 miles....then to monroe michigan on sunday....another 400....we wer sitting outside the gate of the hamfest with the air on for about a half hr, car overheat or peculiar started to balk and stall....would restart and run for seconds then hobbled into the flea market and i was able to get it parked....i then ignored it for the next 5 hrs hoping it mite started one last time and quit like the key was turned off....3 or 4 guys with tools and code readers then flocked to the car and we dug out cap, rotor, cam sensor, ign module, coil, ckp sensor...and replaced with parts bought in spark/start conditon persisted....150.mile tow to my body shop...we changed computer unit next, then started scoping the signal lines of the sensors and came up with the story i started does run now but im not comfortable with the fix....your diagnosis of the wiring to the ckp makes most sense for the problem but we hav something entirely different going on here and ive never seen anything like it in 35 yrs....the ckp sensor removed from the car at the time of the problem was not physically damaged in any way but i have yet to find it in the car because i didnt look hard enuf...i strongly suspect it was a good part tho....something in the engine changed causing a shift in the relative position of the reluctor and sensor...i dont know if it was the engine case or crankshaft or reluctor wheel, but something physically changed which woukd cause multiple ckp sensors not to operate when installed correctly in the provided mounting thats possible is beyond me, but im just making a statement based on the factual evidence....Ill let you know what happens as we go going to buy several ckp sensors of diff brands and do some research on that as well...
Expert:  Jerry Newton replied 2 years ago.
I can tell you that CKP sensor is not that common. If you've replaced a number of them, it's extraordinarily unlikely that they've all been faulty. What I really suspect is that there's something wrong with your timing cover. It's plastic, and I do recall running across a similar condition years ago that ended up being a timing cover failure. This has seemingly been a persistent problem for you, so it is completely possible that someone made a repair years ago that is haunting you now. Namely, if that timing cover has been off for any reason, it should have been replaced. If someone didn't install it correctly, if it's got broken locator pins and is skewed from where it should be, you're going to open that CKP air gap up and find yourself with an engine that intermittently runs. I would have replaced the wiring on this already, just because of the number of wiring issues I've seen on these circuits. If you are 100% convinced that the wiring is not at fault (in my eyes, that means I've at least replaced the pigtail connector and visually checked the rest of the harness for opens or shorts), I would be getting that timing cover replaced. You may remove it and find exactly what I'm talking about: broken locator pins. But you can't see that unless you remove it. In the interim, I like your thinking, use some clay or whatever to measure the air gap. Do some custom modification to the timing cover to decrease that air gap, such as taking some material off the plastic mounting boss, and see if that solves the issue. If so, you will want to replace that cover. This is going to be a wiring issue or a timing cover issue. Nothing else makes any sense.
Customer: replied 2 years ago.
Our shop is primarily body work, although we can replace engines and even occasionally rebuild down to piston rod bearings, but its not an everyday occurance so all these screwy engine problems are usually first time for me...everytime....So u r telling me that the hole that the ckp sensor pokes thru is in a chunk of plastic? Its gotta be cracked....and moving around....just a
Expert:  Jerry Newton replied 2 years ago.
Yes, the timing cover is a chunk of plastic. And it's supposed to be replaced any time that it's removed. AND, if you replace the timing cover, you're supposed to relearn the crank angle using a scan tool. It's likely that none of these things occurred correctly, but even if that stuff is OK, I have still had my butt kicked by a cracked timing cover, which was allowing the sensor to walk around, intermittently either dropping to zero or going up to 15,000rpm on the scan tool, due to the gap rapidly changing. That was a weird one, but you're in weird territory and it's worth mentioning. If this were in my shop, I'd be replacing the wiring pigtail, and probably be looking to replace the timing cover as well.