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post #1 of 6 (permalink) Old 02-16-2017, 11:13 PM Thread Starter
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Cold start pulsating

Hi all,

So this has been happening since Monday. I live in NW Ohio, temps have been in the 30's in the morning lately. I changed the factory fill on Sunday and Monday I went to leave for work and when I put the car in gear and accelerated it was pulsating. RPM's would bounce a few hundred rmp's as I drove. Was really strange, so I stopped and put it in park and turned it off. Started it back up, ran perfect. Next morning same thing, except this time I just gave it some more gas and it fixed itself. Now the past 2 days it does but it's hardly noticeable and only for maybe 5 seconds and then it's good. I don't think it's a transmission problem. No check engine lights or anything. Everything else is just peachy. I've got 2,050 miles on the odo.

Also, another quirk I've noticed is my blower for the HVAC will continue to run even after I've turned everything off. I have to turn it on and off about 3 times before the blower motor finally quits running altogether. It's a small thing but really frustrating because it shouldn't do it all.
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post #2 of 6 (permalink) Old 02-16-2017, 11:23 PM
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Check the relay for the HVAC blower
It may be sticking

Same for the IAC???
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post #3 of 6 (permalink) Old 02-17-2017, 07:29 AM
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Filled up at a different gas station Wednesday night, yesterday morning, engine was really pulsing when I first stated it, only 5K miles on it now, but it cleared up in 30 seconds and was good the rest of the day. Figured I got a little bit of water in the gas that would settle over night. Naturally the fuel input is at the very bottom of the tank.

Last fall, went up north in our motorhome, got gas up there with a lot of rain, that was dumb, put some in both the front and rear tanks, also dumb. When we took off, didn't get very far, engine stalled in no-mans land. Fortunately could pull to the side of the road, had a tool box, and clear gas filters, added an electric fuel pump, and a flash light. Could crawl under, disconnected the fuel line, had my wife switch on the fuel pump until I got clear gas. We made it home okay, but then the rear tank, this I could put in a container. Got out about three gallons of water.

Relay contacts are only used by the radiator fan, blower motor uses a PWM power MOSFET transistor, wow, sure love the speed on this thing.
To me, this sounds like another lack of power on reset problem, BCM will go crazy without a proper microcontroller reset. Sure was the problem with my thermostat heater, but with component tolerances and a ton of computers in this thing, not sure what would go wrong. With my old Cruze, was the radio first, but then the ECU, car wouldn't even start 40 miles from home. But removed the key, opened the door, second time doing this it started. In this thing was the ignition relay, darn thing switches everything on. In my Elantra, was a loose negative battery cable, been perfect ever since. But did check both ign 1 and 2 relays, have precision test equipment for this, they were good.

Never had computer problems before when we didn't have computers, slide rule worked perfectly and nobody could hack it. Never had computer car problems before when before they added computers. Motorola came out with the first processor in around 1970, was a one bit unit, claimed a lot easier to write software than designing hardware. First ones used a separate port for the instruction codes, another for the data. But with a 4 or 8 bit marketing got involved, cost 2 cents extra for a pin, oh my God this is adding 16 cents to the cost!

So multiplexing was used for both ports, just invented the crash, been this way every since. In the 80's, cost 16 cents for a byte, again marketing, only used a two digit year date code, looked what this caused in Y2K. Been told a million times to use a 89 cent microcontroller by marketing, sure, but you only gave me a 4 mm square to put this in. As we know today, hardware cost next to nothing, but watch out for that software that has to be updated every five minutes. $$$$$! Ha, getting carried away again.

Radios use to be radios, now they are computers, When a real blower motor switch was used with resistors, didn't have these kinds of problems, sure do today.

Another little problem was putting in high impedance CMOS technology with less than a volt noise immunity into a vehicle loaded with motors and solenoids that have the Tesla effect, generate extremely high voltage that can mess up this logic. Layout was more of an art than a science, just invented EMI. Took them long enough to get rid of those spark plug wires, another battle between engineers and bean counters, 40KV!
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post #4 of 6 (permalink) Old 02-17-2017, 07:32 AM
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Oh, 150,000 tech jobs were suppose to be created when all this stuff started, yet another problem, have a guy good on replacing a muffler trying to solve these.
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post #5 of 6 (permalink) Old 02-17-2017, 09:40 AM
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Originally Posted by Throt View Post
Hi all,

So this has been happening since Monday. I live in NW Ohio, temps have been in the 30's in the morning lately. I changed the factory fill on Sunday and Monday I went to leave for work and when I put the car in gear and accelerated it was pulsating. RPM's would bounce a few hundred rmp's as I drove. Was really strange, so I stopped and put it in park and turned it off. Started it back up, ran perfect. Next morning same thing, except this time I just gave it some more gas and it fixed itself. Now the past 2 days it does but it's hardly noticeable and only for maybe 5 seconds and then it's good. I don't think it's a transmission problem. No check engine lights or anything. Everything else is just peachy. I've got 2,050 miles on the odo.

Also, another quirk I've noticed is my blower for the HVAC will continue to run even after I've turned everything off. I have to turn it on and off about 3 times before the blower motor finally quits running altogether. It's a small thing but really frustrating because it shouldn't do it all.
With 2,500 miles on the ol' girl, you don't deserve to start your day with "frustrating." IMO, solution is simple: dealer's problem, not yours. Go frustrate him. I wouldn't even get out so much as a toothpick from the toolbox to try and figure it out.

Part of that bottom line on those window sticker prices we paid for is the OEM's 5/60k, 10/100k warranty. Go get your money's worth, young man. There's always the "disconnect-negative-battery-cable-for-15-minutes-reconnect" approach. Everything resets back to factory specs. Not a big deal, except you have to reprogram your radio presets and user menu stuff on the dash.

As an afterthought, if I owned an OBD tool, I "might" go as far as plugging it in to see what code(s), if any, were thrown. Otherwise, it's "phone/appointment time" for me with a trip to the service dept for free coffee. Truth be known, it's really not "free" since we paid for that, too. It just wasn't listed in the MSRP. LOL

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Last edited by OkieRich; 02-17-2017 at 09:51 AM.
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post #6 of 6 (permalink) Old 02-17-2017, 01:53 PM
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With this new stuff, well I guess 1985 isn't new anymore, had to buy one of these.



Fuel Pressure tester, hooked up to the injector manifold, besides testing pressure, has the side valve you can press to get fuel out into a container. To do this, need to have the fuel pump operating. On the Elantra, open that under hood fuse box cover tells you where the fuel pump relay is. Can pull that relay, learn where the contact terminal are and press in a couple of 1/8" terminals, use a clip lead or a starter test to switch on the pump. Run it until you get clean gas.

Sure a problem up here, did a net search, 3,500 gas stations have water in their tanks, law says underground, have a high water table here. Tossing in a couple cans of Heet may help, had to do this with my kid driving back from Milwaukee, got water at a Mobil station, engine was hesitating like crazy. Least we got home, but took a week to clear up. With other kids, stalled, had to grab this tester, drive to where they were, and pump out that water. Not a problem in Death Valley.

Didn't get very much yesterday, this morning, Elly was very happy, could tell the way she was singing.
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