Crank sensor? Has it already been determined there is no spark at the spark plugs when this problem is occurring?
Is the symptom still that it starts ok during cranking, then immediately dies when the key is returned from “start” to “on”? If so, that doesn’t seem like the typical symptom of a faulty crank sensor. The engine computer knows when the starter motor is working (i.e. the key is in “start” and the engine is cranking), vs when the engine is running (after the cranking phase). In some cases the ignition circuitry boosts the spark voltage during cranking compared to just running. Perhaps the problem is in that cranking vs running circuit logic.
One time my ancient carburetor truck had the same symptom. The spark circuity’s power came from a different point during cranking vs running, involved a ballast resistor, and the fault was in the latter. I could visibly see a spark at a spark plug during cranking, but the spark would stop once the key was returned to “on”.
I think it has probably already been mentioned, but this problem could also be caused by an aftermarket “security system”. If there are signs something like that has ever been installed in this vehicle, be very suspicious that’s where the problem actually is.
Okay, so the guy’s an experienced mechanic and you’ve happily dealt with him for years
another possibility . . . he might be getting slightly set in his ways by assuming that certain problems always generate a fault code
It boils down to one thing . . . “the other things” weren’t actually the root cause
I’ll try to be tactful, since you have a pretty good relationship with your mechanic . . . saying the test is the code is a sign the guy might need to hone his diagnostic skills
That’s something that young guy straight out of tech school might say, because he doesn’t yet have any experience
Might be time to crack the books, so to speak
No shame in that
Lots of people get rusty and need a refresher course
Recognizing your deficiencies and working to correct them is important
What made him think it was the mass airflow sensor?
Yes. That is exactly what it is. And it does have spark, it starts and immediately stalls. No sputter, no long crank, fires right up. Dies instantly.
I have brought up crank sensor to him so many times and he is pretty confident it is NOT that.
As far as a security issue, he did suggest that. And he said now theres a “radio” code, but the radio is stock so not sure about that as far as aftermarket installation & security stuff goes…
Is this something testable? Circuit logic? Is that gonna be a really expensive fix? Like new computer expensive?
A code I’m pretty sure. Something about an airflow issue. It was not the air filter, and it was not a vac leak, but he said there was a code. He also gave me the impression it could be a guess, but the car ran after that and so it was a “good guess” but I guess it was not after all. He only charged us for parts, further contributing to my “guess” theory.
There was a code for a faulty battery connection before the airflow code. That’s why he replaced the negative battery cable and connector.
The battery code was gone after that exchange. But then when the problem came back, airflow code showed up. Replaced the Mass airflow and that code disappeared. Now there’s no code.
But apparently codes are not the only thing we should be looking at.
Hes not a “new” mechanic, but I dont disagree that he may be set in his ways. Funny thing is he has 2 guys that work for him too now, younger. One is probably 22 and the other is still in tech school. They’ve all had a whack at throwing ideas at it. Maybe they all need some education.
Security light is NOT on.
He mentioned this, and even used both sets of keys we got with the car. He said chevy could make us one with the vin, but it prob wouldnt matter. Its only $8 to try but its prob not that
Like I said the only time I’ve had a crank sensor problem, it stalled period. Now I did take it in to have the crank checked and they said it was ok. Next day 30 miles out it failed. The shop I towed it to showed me the crack that had obviously been there a while and the guy didn’t see it the day before.
When I have had a MAF sensor issue, it has usually acted exactly like it was starved for fuel. Still ran but just enough to limp home at 10 mph.
My fuel pumps gave me the symptoms you have. Not saying it is not the other issues and never had occasion to have a security system issue, but man fuel pumps do crazy stuff. Crank crank start die. Start, run die. Run just die. Crank crank, pound on the tank with a 5 lb hammer, and start. When my Olds wouldn’t start after sitting for a while, I determined fuel pump and just called the junk yard.
Fuel pump relay could be the problem also. I had that issue in a Golf. The Golf also had two fuel pumps which maybe the Malibu doesn’t but the low pressure pump on the Golf also went stone cold one evening. The relay is a strong suspect as they can get weak, drop out when they get hot and then suddenly start working again later. This kind of thing may not throw a code.
Can a faulty crank position sensor allow a start on crank but give a shutdown on run?
This definitely an electrical issue. Get a large paper clip straighten it out and jump the fuel pump relay leads that go to the pump. Jump it while the key is off as the wire will get really hot, enough to brand you. If it runs now when it didn’t before get a new relay, couple of bucks. If not or if it still happens again it may be the control circuit to the relay or the pump itself is shot. How’s the ignition switch on the column, sloppy loose. Do you or the previous owners drive around with 5 lbs of keys and doodads on the keychain?
Put a voltmeter on the relay control leads. Have someone move, jiggle the key/ ignition switch. If the meter reading is jumping it may be the ignition switch.
If you fix it and the same problem comes back it ain’t been fixed yet.
One other thing. Toyota’s would not run after the battery was disconnected for a time. It would start but you would have to throttle the eng to higher rpm’s to keep it from stalling. It could take about a half hour of driving before the computer would set a proper idle rpm. Is this what’s possibly happening with your car?
Suggest to investigate the radio code further; i.e. until it is fully disproved as the cause. A radio code might imply anti-theft circuitry is the culprit.
Has your shop actually verified there’s a visible spark at a spark plug after they key is returned from “start” to “on”?
I’ve seen this exact scenario on a pick up with throttle body injection. Funny thing is the guy had an identical truck. So I swapped ECUs and problem solved. Best part is that after ECU swap, both trucks ran. Must have been bad ECU connections that got cleaned during swap.
Well…when I was there last time, I made him show me tests on some of the stuff you guys suggested. And out of the blue the car started. Sounds like a good thing, right? Wrong. Cars don’t fix themselves and he said he was in a worse scenario than before with not figuring it out.
Unfortunately everything was coming back OK as far as tests. He turned it off and on a dozen times and it started every time. Rhe next day it didn’t start again… He called a fellow mechanic in to help him troubleshoot, and upon this other guys suggestion, replaced the throttle body and sensor. Well, we have been driving it daily for over a week and so far all is well. Hopefully this issue has been resolved.
He also didn’t charge us at all this time, and apologized profusely for the month+ this took. So I will forgive him, this time.
