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Old 05-23-2020, 12:35 PM   #1
Jon Boy
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Default Need help troubleshooting intermittent hesitation and hard starting

I'm trying to sell my 2001 SC2, but I'm having some random issues with it that I'm having problems troubleshooting.

Two or three times in the last year, I've had trouble starting it. I run an errand, get back in my car, and suddenly it won't start. It'll crank just fine, and there's power to everything, but it won't actually catch. Eventually it starts again after several minutes, and then it runs fine after that. The weird thing is that it happened once about a month ago, and the last time it happened before that was about a year ago, so it's not a frequent thing.

The last time it happened, I depressed the schrader valve on the fuel rail, and it sprayed fuel, so at least it's getting some fuel pressure. And when it happened last year, I rented a fuel pressure gauge from AutoZone, and everything tested within spec. So my guess is that it's not a fuel problem, though I'm not sure what kind of ignition problem would be so intermittent.

I've also had a few random problems with hesitation while driving. A few times I've been driving and then suddenly it hesitates several times in a row like it's about to stall, but it doesn't. Then it keeps driving fine again. And like the no-start problem, it happened once in the last month or two and a couple other times about a year ago, with several months of problem-free driving in between.

I've checked for codes and haven't seen anything that looks relevant in the entire time it's been having issues. I've had a P0410 that I'm still trying to resolve, and I briefly had an O2 sensor code (now I forget which one) that went away when I replaced the upstream sensor.

I feel like I don't have much to go on here, so any help would be greatly appreciated.
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Old 05-24-2020, 12:40 AM   #2
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Default Re: Need help troubleshooting intermittent hesitation and hard starting

An intermittent crankshaft position sensor will cause starting problems especially when hot.
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Old 05-24-2020, 12:37 PM   #3
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Default Re: Need help troubleshooting intermittent hesitation and hard starting

Although not likely, the PCM is a possible culprit. The symptoms you describe sound exactly what I had with a bad PCM.

Do all the simpler/cheaper stuff first, maybe even throw a CKP sensor at it, but if nothing else helps (or the problems become less "intermittent") then I will advise you on some checks you can try regarding the PCM.

Do you have an electrical multimeter and experienced with using it?
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Old 05-24-2020, 12:48 PM   #4
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Default Re: Need help troubleshooting intermittent hesitation and hard starting

As a mechanic, I saw a case wherein a bad engine coolant temperature sensor would cause a no-start condition. The wiring to that sensor could cause the same problems due to corrosion or bad contact at the sensor. It's an inexpensive fix to replace the sensor or clean or change it's plug.

You mentioned changing the O2 sensor. If it was an aftermarket part, it's quite possible that it has failed again.

Also a failing MAP sensor could cause both symptoms that you mention. And it's not especially expensive to replace. And this part could

AND, a sticking EGR valve could cause both situations as well. If sticking open, it could cause a no-start due to leaning out the mixture. And if intermittently sticking, it could cause a stumble while driving, especially after a deceleration and reapplication of the accelerator.

That crankshaft position sensor is a viable candidate for replacement as well. And don't discount a failing ignition module mounted under the coils.

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Old 05-24-2020, 01:59 PM   #5
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Default Re: Need help troubleshooting intermittent hesitation and hard starting

Some great suggestions here but with this erratic random problem, perhaps some basic troubleshooting may help.

A recent Vue member posted of severe issues with many symptoms, none related to each other. His original (drastic) thoughts were either ecm or bcm failure as a person unfamiliar with diagnosing and troubleshooting. His repair shop seemed to replace things with no permanent answer. His final reply was............a severely corroded battery ground cable he suggested to replace by his shop that ignored him. The battery positive cable was replaced but didn't fix the problem. He ordered a factory battery ground cable and had a relative install it. Fixed all his problems.

While checking fuel pressure with fuel spraying out the fuel test port, this doesn't guarantee the fuel pump is operating all the time. Mileage? Fuel pumps can fail anytime or become intermittent. A fuel pressure connected while driving may show an intermittent pump failure at the moment hiccups occur.

The ignition system may be intermittently cutting out if wiring is compromised. Did you go over ignition system wiring to examine it for wear and tear, damage? Cracked insulation, dry rot and weathering can break wires inside insulation with evidence showing on insulation. Wiring harnesses, when new, are flexible and mold themselves to cable runs. flexibility hardens over the years with damage occurring whether visible or not.
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Old 05-25-2020, 12:32 PM   #6
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Default Re: Need help troubleshooting intermittent hesitation and hard starting

I wondered about the CKP sensor, though the only times it hasn't started have been in the spring. It ran fine all last summer, so if it's a heat-related thing, you'd think I would've had a lot more problems when it really started to get hot last year.

My car has the new brass ECTS, and if I remember right, the pigtail on it looks good too. The previous owner must have had it replaced, because I think it was one of the first things I looked at after I bought the car, and it had already been done.

I just changed the O2 sensor within the last 50 miles, so I'd be really surprised if that's the culprit. Also, is it possible for a bad O2 sensor to cause a crank-but-no-start condition, as well as bucking and surging? I don't think I've ever heard that before.

I don't think I've ever replaced the EGR valve or the MAP sensor, though I have taken the EGR valve off and cleaned it pretty thoroughly. I want to say that I've done it within the last year, though I don't remember exactly when it was.

Is there a way to test the MAP sensor to see if it's within spec? I've got a scanner, so I guess I could hook it up and watch the live data on it to see if it's reading normally.

The car has about 146,000 miles on it. I've had it for nine years and haven't replaced the fuel pump, though I have no idea what the previous owner had done to it. I did replace the fuel filter last year after it started having issues, but it didn't seem to make a difference.

If I have an intermittent fuel pump problem, what's the best way to test for it? Like I said, I got a fuel pressure gauge from AutoZone and tested it last year, and everything was within spec. But if it's flaky, I'm not really sure how to troubleshoot that unless I drove it around a while with the pressure gauge hooked up.

I replaced the ICM and coil packs just a couple of years ago with junkyard parts after I had a P0340 error. I didn't really examine the ICM wiring thoroughly, but I didn't see any obvious problems with it at the time.
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Old 05-25-2020, 01:45 PM   #7
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Default Re: Need help troubleshooting intermittent hesitation and hard starting

The O2 sensor cannot affect startup. Cold engine startup; the pcm ignores O2 sensor until the sensor heats up above 600F when it begins outputting signals. During cold engine running/open loop mode, the pcm is waiting for O2 sensor signals. Every cold engine startup doesn't need the O2 sensor and runs fine with our without it. It's after heating up is when the sensor begins sending signals to the pcm. The pcm then enters closed loop mode and fine tunes air/fuel mixtures for tight emissions control. If the sensor was shorted or open, the engine still starts up and runs.

Map sensor can be measured with a multimeter but you'll need specs (aa1car.com). Using a reader with ignition on engine of, it should display local barometric pressure. Your local weather should have barometric pressure to compare your map sensor to. It gets complicated if you try measuring map sensor output and attempt to correlate output to vacuum equivalent. In general, measuring sensor at ambient atmospheric pressure then creating a vacuum should display varying values. The tiny port monitoring the intake manifold vacuum should be clear of debris. A reader can display coolant operating temperatures if there's doubt about the coolant sensor and its wiring. Expect ambient temps before startup and 185F-195F after warm-up.

A fuel pressure gauge is needed to snake the gauge above the hood for observing fuel pressures while driving. The moment the engine stumbles will be the time to observe if fuel pressure dropped.

A soup can gasket can be used to block of ports underneath the egr valve. Drive normally for a few days to see if the erratic engine behavior returns or not. The blocking gasket prevents exhaust gases from entering the intake manifold during egr valve operation (normal acceleration and cruise conditions).
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Old 05-26-2020, 03:19 PM   #8
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Default Re: Need help troubleshooting intermittent hesitation and hard starting

To me it sounds like a TPS is going bad or you have a flood condition from a leaking fuel injector or more than one.

When it wont start do you have spark? Its the first step.

With engine hot and you shut it off what happens to the fuel pressure?
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Old 05-26-2020, 04:09 PM   #9
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Post Re: Need help troubleshooting intermittent hesitation and hard starting

Just a quick look see if the ECTS has a replacement pigtail connector. IS IT SOLDERED OR CRIMPED? It must be soldered as crimp connectors subjected to heat and moisture
can intermittently fail!!

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Old 06-07-2020, 05:55 PM   #10
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Default Re: Need help troubleshooting intermittent hesitation and hard starting

I finally had a little bit of time yesterday to take a look at a couple of things. The ECTS connector is the original, and it looks fine. I don't see any corrosion on it. I'm not sure how a bad ECTS would cause any of the symptoms I've been having, though.

I got a fuel pressure tester from AutoZone, but the gauge is wonky. It was reading about 1015 psi even when it wasn't hooked up. After I connected it, it was reading about 60, and while the car was running it was about 65. Assuming the gauge is just 1015 psi high across the board, it sounds like it's within spec. I didn't try driving it to see what happened if and when it stumbled, though.

And then it started raining pretty hard, so I wasn't able to take a look at anything else. Guess I'll have to wait until next Saturday.
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