Common Problem: warm/hot engine will not start
 

Hello all.


Year: 1991 Model: 190E 2.6L - Car won't start on warm/hot engine

So you've seen this hot-engine don't start issue posted probably a billionth time already but there's always something new. I've already scoured the forum and net and tried everything suggested swap/replaced parts to no avail.

The engine starts really nice, on one crank, when the engine is cold. After it's been running for awhile or engine reached operating temperature, I turn off the engine and won't start again...not until it had a chance to cool off.

Now, here is a twist...while the engine is still warm/hot, when I removed the cold start valve or injector(CSV), and after a few crank, the car starts fine and it does start again on one-crank on subsequent starts even when the engine still hot just as long the CSV is out.

So it looks like the engine was starving for air - it needed air but it wasn't getting it so it won't start. That doesn't mean the CSV is bad but removing it allowing air to pass through and helping the engine start seems like a clue.

So when engine is hot and won't start, it's either not getting enough air to lean the a/f ratio or too much gas going in.

I've read through numerous forums describing similar hard/no-start on hot/warm engine and replaced every part they mentioned that fixed their problems but my issue still exist.

Parts I've replaced so far:

- crank position sensor(new)
- coolant temperature sensor(the 4-pin, new)
- auxiliary temperature sensor(the 2-pin, new)
- cold start valve(new)
- fuel pressure regulator(fpr), fuel pump and filters and the fuel accumulator are about 5-6 years old - no leaks here
- fuel injectors are about 4-5 years old - no leaks
- EHA no leak (original) - idle control valve (3-4 yrs old) - tested with spare, no change

- OVP works - tried spare but no change

- Ignition coils, plugs, caps, rotors all new

Fuel pump works well even when the pins 1-2 bridge. Fuel pressure is good, no leaks as far as I know.

I also replaced my MAS and ECU with "used" units while the engine is having hot hard-start issue to no avail - I can't tell for sure whether the use parts are in good working order or not but I tried almost anything and I've ran out of ideas.

Again, when cold, engine starts very nicely with one crank and even idles nicely for awhile until it reaches operating temp. I've replaced most, if not all temp-related sensors on engine but no go. I'm probably one bad-part away from the fix but finding which one without throwing more money at it is the last big one.

Has anyone ran into this issue before? hot-start engine fail to start but with cold start valve out, engine starts fine.

Any help or suggestion is appreciated. Car been in garage for over a month now and I'm in the borderline of selling the car to our local JY for scraps.


Please help!


jav

Sure sounds like typical cps problem but you have replaced it.

When did you change plugs/cap/rotor/wires and what brand did you buy?

sure sounds like a typical fuel pump (MAS) relay issue to me. If you were having fuel related issues, you should be having running problems too as the engine heats up. A used relay can easily have the same crappy solder problems that your original one did. Open one up and look for poor solder joints. Google the issue, there are plenty of pictures and threads out there on how to repair it.

Just for clarification, I was on the road when the engine decided to cut-off. It wouldn't start after that. I had towed and it's now sitting in the garage, starts happy when it's cold and idles nicely for awhile. I dare not drive it out until this issue is fixed...don't want to wait hours and hours for engine to cool off.

Parts listed as "new" were bought online not more than a month old. When Bosch is available, I buy it first. Otherwise, what ever comes next. The fuel systems are all Bosch, or at least it had the Bosch name or brand on them.

I also checked resistance or continuity, where appropriate, for all items I bought and compared with the original component and I can say they're almost all identical. In other words, the items I bought to fix the issue didn't do nothing. Therefore, I now have tons of spare parts.

As for the MAS relay, I had one spare where I took off the cover and looked inside and found no corrosion or the like, installed it but no change.

So, what's chocking the engine when engine runs at operating temperature? ICV?, it spins freely with a 9V battery test but perhaps what's controlling it could be defective but what is it?

Still sounds like CPS. Maybe have someone check it again.

Unplug the EHA and drive it like that for a few days and see if the problem is gone. Usually if the car suddenly dies while driving it's fuel related. If car dies while you are coming to a stop or decelerating it might be the EHA, so disconnect that and see if the problem goes away for a few days, then plug it back in and see if the problem returns if it is gone.

Hi tyl604

The new CPS is measured at 873 ohm. The original has 875 ohms. They're almost identical.

My understanding of the CPS is it transfer crank position via magnetic pulse through the cable and into the EZL.

Can you please explain your idea why you think it's the CPS?

Thanks for your interest... keeps me going and not giving up. : )

Hi Ismalley, thanks for your suggestion. I'll give that a try but I will not be driving it out of the garage; it's now unpredictable and it could mean disaster on the road.

Every test I've done was to confirm the engine will start after it reached its operating temperature and that it will start right up without hesitation. When I achieved that goal, only then will I take it out for a test drive.

In the morning, I will let it run without the EHA and let it reach 80+C and see how it will respond.

Thanks for the suggestions... please keep it coming... I need 2, 3, 4th+n brain to get this fixed! : )

I really think you should have a look at your cap and rotor. In my experience with the m103 engine, oe wires last 5 years, oe cap and rotor about 3-4. Plugs regardless every year. Bosch stuff lasts half as long, and the rest fail almost immediately. (Months later).

I had a m103 that had something jacked up with the ignition coil and kept burning up my cap and rotor. Symptoms exactly like what you are having. New (used) coil and the problem is gone.

These engines are just fancy carburetor engines. Don’t overthink it. Let it warm up and when it stalls, and won’t restart, spray some gas in the intake. That will let you know in 2 seconds whether you have a fuel or spark problem

About two years ago the stock Bosch ignition coil died on me - 0 ohms on all posts(prim/sec). I decided to run it with MSD Street Fire CDI and MSD Blaster 2 coil...and yes, it works and it works well for over two years. I thought well, maybe it's the MSD...and I do have another Bosch ignition coil in my parts bin that I know works well before this stuff happens, put it in, but the hot-start problem still exist...so no, it's not the MSD.

The cap and rotor are of Bosch brand and they are new - less than a month old. The one before that was also a Bosch brand about 2 years old - decided to replace anyway, but problem persisted.

I wish what you're saying was that simple of a solution but unfortunately not in my case.

The only things thats not "new" are the MAS, ECU, EHA, or EZL... won't throw money into this if there's no certainty that it will fix my problem. I bought used "MAS" ECU" and "EZL" but none of them resolved the problem either....it could be that they are defective themselves, who knows.

Anyone from the St. Louis, Missouri area who wants to lend me some parts for testing? I'll do the same for you... : )

Or if anyone want to lend me your known MAS, ECU, EHA, or EZL, I'll pay shipping both ways and pay you $$ just for letting me test. hehee...yes, I'm that desperate, and yes, I'll send your original back. DIY pinky promise : )

Parts I've replaced so far:

- crank position sensor(new)
- coolant temperature sensor(the 4-pin, new)
- auxiliary temperature sensor(the 2-pin, new)
- cold start valve(new)
- fuel pressure regulator(fpr), fuel pump and filters and the fuel accumulator are about 5-6 years old - no leaks here
- fuel injectors are about 4-5 years old - no leaks
- EHA no leak (original) - idle control valve (3-4 yrs old) - tested with spare, no change

- OVP works - tried spare but no change

- Ignition coils, plugs, caps, rotors all new

Fuel pump works well even when the pins 1-2 bridge. Fuel pressure is good, no leaks as far as I know.

I had a similar problem with my '88. It was intermittent, but got worse with time. I ran a simple on-the car-test and found that the fuel accumulator had an internal leak, which means it wouldn't hold pressure. Fuel just short circuited back into the hose from the fuel tank. With a new Bosch accumulator, starting behavior retuned to normal.

I documented the test along with a destructive failure analysis of the accumulator that clearly showed the internal diaphragm was cracked. Search for threads started by me and consider running the simple fuel accumulator test even though it's not that old.

Duke

My SL stalls on me , so frustrating and scary in traffic, I had a 91 300E that would do that, replaced tons of parts, still did it, turned out to be the dist rotor was bent a tiny bit, when it heated up it it would bend more and lose proper position killing spark, then bend back when cooled and all OK.

with my SL it is random stalling, didn't know if it was fuel or electrical, finally bought a cig lighter plug in Volt meter, cheap $16, Autohauz AZ has it, found my voltage was going below 12 volts killing power to modules , those can't run on low voltage and car dies, bought new alternator/ voltage regulator, better but still stalling, pretty sure its my ignition switch now causing issue, good luck.

Been there - done that.


Faulty fuel accumulator - one of the more common causes of warm/hot starting issues as per countless threads here over the yrs.