Dyno says 113HP, belt gets thrown off, what say ye?

[DrWin]

Hi guys,

I have a few questions I'm hoping for some input on.

So - basically I'm gonna have to do some engine work this winter. I have no idea how far I'm gonna have to delve into the engine before I'm done, and just to have some reference for when it gets back to running order, I decided to have it dyno'ed. After one run the engine threw the belt for the water pump/alternator and boiled off 6 liters of coolant, so we left it at that. I got home safely after putting the belt back on and refilling the coolant.

The reasons I'm going to go into the engine in the first place is that I have had a small coolant leak, that has escalated to a rather more substantial coolant leak. It originates somewhere inside/under/behind the water pump. Also I have had the rather unpleasant surprise of the engine stopping without warning a couple of times, always on level road, going steady at around 80-90km/h, steady throttle, all guages normal until.... ....engine stops. When I restart the car it immediately dies - unless I keep the RPMs at around 3000-4000 for 1 minute or 2. After that I can ease off the gas until we reach normal idle, and the the car starts acting totally normal again. (Until next time the engine dies mid-cruise.)

Are the diverse symptoms somehow related, in the minds of people who know about cars in general and/or DeLoreans in specific?

Water leaking from around water pump somewhere.
Engine threw the belt for the water pump/alternator when dyno'ed
Engine has tendency to mystery-quit when cruising
Dyno says 113HP (tech says that is at the engine)



67159

[WHO1DMC]

My thoughts on the belt. 1. The pulleys are off ever so slightly. 2. The type of belt you're using is expanding do to the speed. As you know our engines don't have a automatic tensioner to take up the slack.

[Bitsyncmaster]

My guess to engine dying would be bad fuel pump. I say that because not much else in the fuel system could cause the stated results you get. I don't think it's ignition related.

[Ron]

The leak and belt sounds like they unrelated to the other problems.
I agree WRT alignment and would check it closely before fixing the leak/pump.

Does it start right up after it dies...without a jump?
Smell rich/lean during the 1-2 minutes before it you can get it to idle?
Run ruff even at the high RPM?

Agree, it doesn't sound like common ignition problem.

A bad pump (as with most electrical problems) usually takes a while to cool off before it starts working again, and, running it right after it quit would keep that from happening. But it sounds like the best bet so far to me too.
...Next time it does it, you might try immediately switching the key off, as soon as it is safe to do so, then checking if it has pressure at the plate before trying to start it.

[FABombjoy]

Interesting data point regarding accessories consuming about 8nm (6ft/lbs).
I'm guessing that explains the sudden increase in torque at 4900 RPM :D

I would think the appearance of the belt remains might help explain the failure mode.

[DrWin]

My thoughts on the belt. 1. The pulleys are off ever so slightly. 2. The type of belt you're using is expanding do to the speed. As you know our engines don't have a automatic tensioner to take up the slack.

Ok, thanks. Ad 1: Is there a way to test that w/o dyno'ing the car and checking to see if it throws off the belt? Visual? Special tool? Ad 2: I'm using the one I got from deloreango for the purpose, what ever they are/were. Could it be that I just haven't tightened the belt enough? I think that is the third obvious thing that could have caused it. Tight enough for normal use, but not tight enough for running the car flat out? (Which I have never done before.)

I have "locating/creating a turnbuckle style alternator tensioner in SS" on my winters to do list. That way I should become able to at least tighten it enough by hand, as a one man job.

[DrWin]

My guess to engine dying would be bad fuel pump. I say that because not much else in the fuel system could cause the stated results you get. I don't think it's ignition related.

Fuel pump sound like a reasonable candidate for causing trouble. It's the old style one, but a brand new one I've installed last winter. I have had one occasion (after spinning out on a closed track) where I was unable to get the fuel pump running again until I had it removed from the car and sucked petrol through it to get it rotating again. Since then it has worked, but IIRC this problem has only existed since then. Maybe spinning the car wildly damaged the pump?

Could a drop in voltage from the alternator have caused the pump to stop? Or would it just keep running on the voltage supplied directly from the battery?

[DrWin]

The leak and belt sounds like they unrelated to the other problems.
I agree WRT alignment and would check it closely before fixing the leak/pump.

Does it start right up after it dies...without a jump?
Smell rich/lean during the 1-2 minutes before it you can get it to idle?
Run ruff even at the high RPM?

Agree, it doesn't sound like common ignition problem.

A bad pump (as with most electrical problems) usually takes a while to cool off before it starts working again, and, running it right after it quit would keep that from happening. But it sounds like the best bet so far to me too.
...Next time it does it, you might try immediately switching the key off, as soon as it is safe to do so, then checking if it has pressure at the plate before trying to start it.

WRT alignment? That is alignment of the pulleys for the water pump / alternator, right?

Yeah, It starts instantly and dies immediately unless I keep it at 3-4000 rpms.

I haven't noticed a difference in smell when doing it.

No, I think my engine runs ruff at low rpms, but runs smoother and smoother the faster I'm going. Kind of like the engine always sounds like its close to stuttering and sputtering out at idle / manoeuvring speeds, but the fast it goes, the less engine noise I get and the less vibration.

Please elaborate a little, "check pressure at the plate", what plate where?

[DrWin]

Interesting data point regarding accessories consuming about 8nm (6ft/lbs).
I'm guessing that explains the sudden increase in torque at 4900 RPM :D

I would think the appearance of the belt remains might help explain the failure mode.

Good point, I think I'll pull that off and have a closer look.

[DrWin]

My guess to engine dying would be bad fuel pump. I say that because not much else in the fuel system could cause the stated results you get. I don't think it's ignition related.

The A/C compressor cycling on couldn't possibly draw enough power to strangle the fuel pump, could it?

[Ron]

WRT alignment? That is alignment of the pulleys for the water pump / alternator, right?Yes.


Yeah, It starts instantly and dies immediately unless I keep it at 3-4000 rpms.It starting instantly indicates the charging system-battery is probably OK.


No, I think my engine runs ruff at low rpms, but runs smoother and smoother the faster I'm going. Kind of like the engine always sounds like its close to stuttering and sputtering out at idle / manoeuvring speeds, but the fast it goes, the less engine noise I get and the less vibration.Sounds like cylinder(s) not firing/missing. You might try pulling plug wires one at a time while it is idling and listen for any that do not change the sound of the engine.
A good test to perform while it is forcing you to hold it at high idle to keep it running too.


Please elaborate a little, "check pressure at the plate", what plate where?The air metering plate (where the air cleaner/breather leads to)....If it dies and you immediately switch it off, no resistance when you press down on the plate would indicate a a loss of fuel pressure (bad filter, pump, restriction, etc).

[Bitsyncmaster]

The A/C compressor cycling on couldn't possibly draw enough power to strangle the fuel pump, could it?

Would not think so. But with the AC on your cooling fans are running which are a high current draw. Just do a voltage test at the fuel pump with the AC on to test that condition.

[DrWin]

Yes.

It starting instantly indicates the charging system-battery is probably OK.

Sounds like cylinder(s) not firing/missing. You might try pulling plug wires one at a time while it is idling and listen for any that do not change the sound of the engine.
A good test to perform while it is forcing you to hold it at high idle to keep it running too.

The air metering plate (where the air cleaner/breather leads to)....If it dies and you immediately switch it off, no resistance when you press down on the plate would indicate a a loss of fuel pressure (bad filter, pump, restriction, etc).

Roger. I'll have to look for that, both the pressure at the plate and the non-firing cylinders.

[DrWin]

Would not think so. But with the AC on your cooling fans are running which are a high current draw. Just do a voltage test at the fuel pump with the AC on to test that condition.

Right, that should be easy to test. Thanks. :)