Engine seized after injector failure
 

Last weekend, the engine of a racecar I own with some friends seized during a race. There was a sequence of events that could have caused the problem but I have some doubts about what really happened and would be really glad if you could offer your point of view.

The events were as follows:

- Engine running strong for 30 laps when driver complains about a couple of slight hesitations of the engine. Driver complains about loss of power and decides to pit. Driver completed about 2 laps since the first complaints of engine hesitations.

- A cylinder is not working even though there is spark. Turns out to be an electrical problem with the injector. A repaired injector cable makes the engine run smoothly again.

- Car goes back to the track and 6 laps later the engine seizes while braking at the end of the straight.

We haven't done a full autopsy yet but a quick look showed significant vertical scoring in the cylinders. The cylinder that had previously had the injector failure was not the one with the worst scoring.

Is it possible that the injector failure caused the engine to seize shortly after? I'm not able to find a reasonable explanation to connect both events...

I doubt that the injection problem was involved in the seizing of the engine. The pistons basically locked up in the cylinders. Usually it’s due to overheating. Pistons expand and friction goes up, expanding the pistons even more until they seize.

That's exactly my thinking. I have a hard time to see how the injector problem could cause an overheating.

Is it possible that the electrical problem in the injector caused a lean mixture in that cylinder?

just speculation
if the injector does not fire there is not fuel, if no fuel then no combustion thus no heat.

engine seizure would be oil related I would think.

will it turn over after it cooled.

remove the plugs and see if it will turn over. see if it will turn backwards.
one possibility although very slight is too much fuel and it hydro locking

Did the injectors stick open, or just quit working? If they stuck open, that would have flooded the cylinders and gotten in the oil.

OP says there is scoring in other cylinders too. It’s hard to imagine how a single bad injector would cause that. Sounds like something else was also going on. Engine/oil temp and oill pressure were OK?

You would be surprised how quickly a stuck open injector can fill up the crankcase. It dilutes the oil and it loses its lubricating properties

I don't think the injector caused this. I have seen cylinder damage due to fuel wash. It takes a TON of liquid fuel and crank revolutions to wash out the cylinder enough to score it.

This requires a faulty ignition, not injector.

A stuck open injector will usually only cause failure by flooding the cylinder and hydrolocking the cylinder. This will bend a rod, in extreme cases.

What is the "injector cable?"

Was this engine recently rebuilt?

I would also think that it's oil related. Will check again if it turns now that is cold.


The electrical signal was not arriving cleanly to the injector. I believe that if no voltage is applied to the injector it remains closed. Is this right?


The driver did not report any abnormal temperature or pressure but it is possible that he may have missed it while racing other cars. We are pretty new to racing and quite overwhelmed by traffic!


We drained the oil and it was totally clean. No metallic particles caught in the magnet or fuel odour.


The electrical cable running the wires to the injector (EFI).


Yes, it had been rebuilt 30-40 hours before the failure but most of the electrical system had not been renewed :(

Race motor:
Type of ignition system?
Type of injection system?
Oiling system stock?
Outside air temp?
Since the seizure occurred during heavy braking, it follows that the engine was at peak power just prior to the braking event, causing maximum heat. It might be possible that upon lifting on the throttle and reducing engine rpms the resultant cooling air reduction over the cylinders caused them to overheat and finally seize. Braking could have unported the oil feed, but that’s not likely in a dry sump system. It would on the seem surface, you are running the internal temperature at the limits of the cooling systems ability to remove the heat from inside the engine and the intermittent injector operation caused a lean condition adding heat to the entire system, ironically the cylinder showing the least amount of scoring was the one with the malfunctioning injector. The possibility that the intermittent operation of that cylinder is what allowed it to add heat to the system via detonation. Detonation produces a tremendous amount of heat in a very short time, and this could have overwhelmed the cooling system and the subsequent seizure.
I did stay in a Holiday Inn Express once....

Can you post pictures? Did you send out an oil sample for analysis?

The fuel injectors get constant power. The ecu sends a ground pulse to fire the injector. I had a mega squirt ecu injector drivergo bad and it dumped fuel into the passenger side bank. That’s about like turning a water hose on inside the cylinder. It filled up my exhaust and dumped into the sump. Definitely not ideal. Especially at high RPMS. It’s also hard on the rods. This condition can also cause hydro lock

Lean mixture at high revs? I have seen this in snowmobiles and motorcycles. The pistons melt and streak the bores.

Yeah, that much fuel would still be in the crankcase and be very obvious. I think this has more to do with heat/lack of lubrication than fuel.

A dead cylinder is an air pump into the exhaust, which gets a lot hotter......

Id say it was an oil problem. You didnt mention what kind of engine?

I don't have pictures at the moment but will take some as we disassemble the engine in the following weeks. I'm planning to send an oil sample for analysis.


Does this mean that if the injectors see no voltage the stay open?


That's a possibility I envisage. If the injector worked only intermitently maybe it caused a lean mixture...


That's also my feeling but the fact that the injector failure and the engine seize happened one right after the other makes wonder if there is a connection between the events.


But if there is a dead cylinder, do the piston and cylinder walls get hotter in a way that could cause the engine to seize?

It's a 944 NA engine. I realise that this is off-topic in this forum but since this is the best forum I know about technical questions, I decided to post here to leverage the general engine knowledge available in this forum.

If a cylinder runs lean it can overheat and detonate, both of which can cause all sorts of serious issues. Seriously overheating a cylinder or severe detonation can cause mechanical failures that would seize a motor. I just can't see either happening without obvious evidence in the oil and obvious damage visible in the plug.

A "stuck wide open" injector can not dump anywhere close to enough fuel to hydrolock a cylinder while it is running at speed. That would take gallons a minute. It would also be pretty obvious because the exhaust would probably be like a flame thrower. http://forums.pelicanparts.com/suppo...amingdevil.gif
An inoperable injector won't do immediate damage either. Hell, in 86 our team finished Daytona on five cylinders with no serious problems.

It isn't a normal situation but my guess is that you have two separate failures. There isn't an advantage (other than curiosity) guessing early why things failed. You're going to have to open it up and do an autopsy.

Sadly, I have sold my share of the car and it is unlikely that I will be able to see the internals of the seized engine.

Thanks for your help and apologies for not being able to post pictures of the damage!