what fixed YOUR hot no start ?

E28 technical advice asked and given! Troubleshooting, modifications and more.
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Sh00bs
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what fixed YOUR hot no start ?

Post by Sh00bs »

yeah yeah another no start when hot post.

YES i've read the other threads but they all sort of seem to just fizzle out without really saying what the issue was, except the DME.

on my '84 528e, it cold starts amazing. you look at the key and she fires up, it'll idle all day long holding perfect temp. blows cold ac, heat comes and goes in waves... might have air bubble, idk.
it will NOT hot start to save it's life. ive replaced the O2 sensor, cap and rotor, plug wires (plugs too), coil,
just did a new thermo sensor (2 prong), i guess im going to do those two bellhousing sensors next then the DME if it's not them?

it has a brand new battery and cranks super fast. it's a shame bc it cold starts so well and runs fantastic. im going crazy trying to figure this out.

so what fixed Your hot no start issue on your e28 ?

also in today's day - 2023, what ecu repair would you send your dme to ?

thanks!
Aldo525
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Re: what fixed YOUR hot no start ?

Post by Aldo525 »

Maybe one of this: (Haynes)

Image

Some fuel issue, pressure regulator????
Sh00bs
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Re: what fixed YOUR hot no start ?

Post by Sh00bs »

so i have a brand new air filter, new fuel filter, new inline pump and in tank pump.

my regulator isnt broke (no fuel in vac line) but i suppose that doesnt mean that it's not bad. again, if it was bad would it cold start perfect ?
1st 5er
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Re: what fixed YOUR hot no start ?

Post by 1st 5er »

CTS bad or possibly unplugged.
Mike W.
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Re: what fixed YOUR hot no start ?

Post by Mike W. »

A 535 not an eta, but mine had a very difficult to start when warm, condition when I got it. It would restart if it was right away, but if I went into a store for a few minutes it was hard to start. Easy clue was the odor of gas when it did start. My injectors were leaking and it was flooded. When cold, the extra gas wasn't a problem because it was cold. If I started it back up right away, it didn't have time to leak enough, but give it a few and it was trouble.

Long shot, but easy to test with the sniff test.
Last edited by Mike W. on Mar 23, 2023 4:49 PM, edited 1 time in total.
tn535i
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Re: what fixed YOUR hot no start ?

Post by tn535i »

My car was behaving badly hot and even random stumbling at times once running. Cold starts were great but there was still occasional stumble as it warmed up. I suspected the cold start injector so I disconnected that fuel line and plugged it. Problem solved.

If the CSI leaks the longer it sets the more fuel gets into the intake making a hot/warm start more and more rich. I needed to crack the throttle quite a bit on warm/hot starts so it could clear itself out faster. If I didn't apply some throttle it may not start and I feared it might foul the plugs.

Since I was into it for the first time in a long time I realized I also had new plugs, cap and rotor to put on it so I did. Cold starts are not as quick now but otherwise it's been running like a champ ever since.

My old 535 gets very little attention these days and this problem had been getting worse and worse for at least a year or more as I was just lazy about it as long as it would go. When I do work on the M30 I still appreciate how simple these systems are to troubleshoot and fix. But the Haynes stuff above is probably not worth quoting.

I also had some fuel smell but that turned out to be no more than a weeping connection on the rail which I tightened.
Sh00bs
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Re: what fixed YOUR hot no start ?

Post by Sh00bs »

1st 5er wrote: Mar 23, 2023 10:26 AM CTS bad or possibly unplugged.
CTS is cold start .... solinoid ?

if i didnt mention it, i bypassed my Cold start valve as mine was stuck open and it clearly does Not need the CSV for cold starts at all. fires right up, ildes perfect.
i also left out i had my fuel injectors cleaned out and tested. that was my main issue when i first got the car with it not running.

with that being said im leaning towards DME, which is odd... but im not sure what else to check
Aldo525
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Re: what fixed YOUR hot no start ?

Post by Aldo525 »

CTS is cold start .... solinoid ?

if i didnt mention it, i bypassed my Cold start valve as mine was stuck open and it clearly does Not need the CSV for cold starts at all. fires right up, ildes perfect.
i also left out i had my fuel injectors cleaned out and tested. that was my main issue when i first got the car with it not running.

with that being said im leaning towards DME, which is odd... but im not sure what else to check
[/quote]

CTS: Coolant Temp Sensor....this sensor gives the temp data and signal to the DME. Maybe bad readings when engine is hot. #13 in the picture, OEM 13621357414

Image
Aldo525
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Re: what fixed YOUR hot no start ?

Post by Aldo525 »

Another clue taken from a german forum:

"Swap the main relay....on the side of the fuse box. My e28 & e30's did the same thing. Typical that it sh**s the bed when hot."
Sh00bs
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Re: what fixed YOUR hot no start ?

Post by Sh00bs »

Aldo525 wrote: Mar 24, 2023 7:44 AM CTS is cold start .... solinoid ?

if i didnt mention it, i bypassed my Cold start valve as mine was stuck open and it clearly does Not need the CSV for cold starts at all. fires right up, ildes perfect.
i also left out i had my fuel injectors cleaned out and tested. that was my main issue when i first got the car with it not running.

with that being said im leaning towards DME, which is odd... but im not sure what else to check
CTS: Coolant Temp Sensor....this sensor gives the temp data and signal to the DME. Maybe bad readings when engine is hot. #13 in the picture, OEM 13621357414

Image
[/quote]


i just replaced # 13, i didnt think a coolant temp sensor affected hot starts. pretty cheap, i'll throw money at that

yes i did swap relays already. no luck
1st 5er
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Re: what fixed YOUR hot no start ?

Post by 1st 5er »

Sh00bs wrote: Mar 24, 2023 10:26 AM
Aldo525 wrote: Mar 24, 2023 7:44 AM CTS is cold start .... solinoid ?

if i didnt mention it, i bypassed my Cold start valve as mine was stuck open and it clearly does Not need the CSV for cold starts at all. fires right up, ildes perfect.
i also left out i had my fuel injectors cleaned out and tested. that was my main issue when i first got the car with it not running.

with that being said im leaning towards DME, which is odd... but im not sure what else to check
CTS: Coolant Temp Sensor....this sensor gives the temp data and signal to the DME. Maybe bad readings when engine is hot. #13 in the picture, OEM 13621357414

Image



i just replaced # 13, i didnt think a coolant temp sensor affected hot starts. pretty cheap, i'll throw money at that

yes i did swap relays already. no luck



CTS sends the signal which initiates the fuel/air mixture cycle.
If you're getting a cold reading when hot you'll get a flooding condition.
A no connection to the sensor sends a cold signal, thus my "possibly unplugged" comment.
tn535i
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Re: what fixed YOUR hot no start ?

Post by tn535i »

The CTS has little to do with starting and more to do with how it runs throughout the cold to warm transitions. A new CTS is not a bad idea as they can get out of spec. But hot running would be terrible if the CTS were the real problem, meaning as it warmed up it would get worse and worse. Unplug the CTS when it's warm and see how badly it runs. So I don't think this is it unless it begins to run terrible as it warms up and then will not re-start.
1st 5er
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Re: what fixed YOUR hot no start ?

Post by 1st 5er »

tn535i wrote: Mar 24, 2023 6:05 PM The CTS has little to do with starting and more to do with how it runs throughout the cold to warm transitions. A new CTS is not a bad idea as they can get out of spec. But hot running would be terrible if the CTS were the real problem, meaning as it warmed up it would get worse and worse. Unplug the CTS when it's warm and see how badly it runs. So I don't think this is it unless it begins to run terrible as it warms up and then will not re-start.


I'm no expert, but poor running as it warms sounds like TTS.
Doesn't the TTS have the 3 signals function as coolant warms.

A friends S38 was exhibiting the no-start when hot which he chased for weeks. Finally out on a drive when it happened we started checking sensor connections. When we came to the CTS the plug was laying squarely on top of the sensor. After plugging it in, a few long cranks later we had black smoke upon start-up and an ///M5 back in the chase, thus my comments.
Mike W.
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Re: what fixed YOUR hot no start ?

Post by Mike W. »

1st 5er wrote: Mar 24, 2023 6:34 PM
I'm no expert, but poor running as it warms sounds like TTS.
Doesn't the TTS have the 3 signals function as coolant warms.

A friends S38 was exhibiting the no-start when hot which he chased for weeks. Finally out on a drive when it happened we started checking sensor connections. When we came to the CTS the plug was laying squarely on top of the sensor. After plugging it in, a few long cranks later we had black smoke upon start-up and an ///M5 back in the chase, thus my comments.
Thermo Time Switch only affects the cold start valve and only has the potential to do so while cranking. It's emphatically a cold start device.

The coolant temp sensor does affect running at all temps.
1st 5er
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Re: what fixed YOUR hot no start ?

Post by 1st 5er »

Mike W. wrote: Mar 24, 2023 6:51 PM
1st 5er wrote: Mar 24, 2023 6:34 PM
I'm no expert, but poor running as it warms sounds like TTS.
Doesn't the TTS have the 3 signals function as coolant warms.

A friends S38 was exhibiting the no-start when hot which he chased for weeks. Finally out on a drive when it happened we started checking sensor connections. When we came to the CTS the plug was laying squarely on top of the sensor. After plugging it in, a few long cranks later we had black smoke upon start-up and an ///M5 back in the chase, thus my comments.
Thermo Time Switch only affects the cold start valve and only has the potential to do so while cranking. It's emphatically a cold start device.

The coolant temp sensor does affect running at all temps.
Now I know.

Gracias!!!
LeiseyJr
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Re: what fixed YOUR hot no start ?

Post by LeiseyJr »

A new main fuel pump, the check valve inside was bad.

It would start just would take about 5 seconds or so when hot, but not hot. 30-90min hotish restart.
Blue Shadow
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Re: what fixed YOUR hot no start ?

Post by Blue Shadow »

CTS let's the ecu know how much fuel to use based on temperature.

I had an M30 that started great cold but the idle would start going up as the engine warmed to eventually idle at about 1200. It would not hot start. There was a bad connection at the CTS, cleaning it fixed the problem.

But these cars were 'repaired' by BMW if one complained about a rough idle back in the day. The solution was to install a resistor in the CTS circuit, usually in the boot of the connector to tell the car it was a bit colder than it really was, a bit more fuel but not much, just enough to cure the rough idle. If this resistor install has failed open the CTS is not talking to the ECU and in the M30 would have great cold start, high warm idle and difficult or impossible hot start.
Sh00bs
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Re: what fixed YOUR hot no start ?

Post by Sh00bs »

talking to some friends, they said they had the same issue's and a crankshaft position sensor fixed it. so i ordered one of those.... i havent tested the ohms when cold (or hot)
we'll see. it's wild. it runs so great when cold, and will run for what seems life forever after firing up. perfect temp, happy as ever. the second you turn it off and try to restart, just cranks.... cranks cranks cranks :( so weird.
Sh00bs
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Re: what fixed YOUR hot no start ?

Post by Sh00bs »

WELP.

replaced the CPS - crank position sensor. it was the LOWER of the two on the bellhousing. no more hotstart issues!

it would run forever when starting cold, fully warmed up, longest i ran it was about an hour and a half.... if you shut it off, INSTANTLY it would Not start back up.
CPS replaced, boom good to go! thanks all for the insight. hopefully this thread will help someone else in the future
Mike W.
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Re: what fixed YOUR hot no start ?

Post by Mike W. »

That makes sense. One of them, the reference sensor I guess, is only used on start up. Literally you can unplug it once it's running and it will continue to run, because once it's running the speed sensor is counting the teeth on the flywheel to fire the ignition and pulse the injectors.

Long story I won't bore you with how I found that out.
1st 5er
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Re: what fixed YOUR hot no start ?

Post by 1st 5er »

Sh00bs wrote: Apr 04, 2023 6:48 AM WELP.

replaced the CPS - crank position sensor. it was the LOWER of the two on the bellhousing. no more hotstart issues!

it would run forever when starting cold, fully warmed up, longest i ran it was about an hour and a half.... if you shut it off, INSTANTLY it would Not start back up.
CPS replaced, boom good to go! thanks all for the insight. hopefully this thread will help someone else in the future
Thanks for posting the solution.
So many here and abroad, other forums, don't report the fix.
tn535i
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Re: what fixed YOUR hot no start ?

Post by tn535i »

I am late to check back. Good catch and good you report back. Now that I hear it this makes perfect sense.

I had a component that would fail on another vehicle when hot. Ok if it was running but no restart. I had to poor cold water on it to get the car to start again a few times until I got the replacement.
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