Perplexing Car Problem

Going back to your original post - 'the car was being driven and suddenly died'. After the starter is released the engine runs backwards for a couple of revs. All engine functions have been checked and appear normal?

My theory is a build-up of pressure in the exhaust system due to a blocked exhaust pipe, this would push the cylinders backwards when the starter torque stopped.

This has happened to me twice in 50+ years of driving. Once when kids rammed a potato up the end of the exhaust pipe and the second time when I tried to do a three point turn in a narrow lane. The exhaust pipe went into the bank at the side of the lane and a plug of clay blocked the exhaust. Both times it took a while to work out why the engine wouldn't start. Some 5 cylinder Audis have a Lamda sensor which means they have a catalytic converter and this might have got blocked?

Get someone to put their hand over the end of the pipe while the engine is turned and check there is good pressure against the hand. The exhaust pipe may be blocked enough to stop the engine from firing up properly, but still allow some gas to escape. You should be able to feel this on your palm, ie the pressure will slowly reduce after the engine stops turning.

lol

seen that happen too

" U turn on narrow road rams mud up exhaust "

however when it occured the engine would start and run for 4 - 6 seconds before spluttering to a stop

:)

ps . also seen exhaust crushed or partially crushed by big speed humps and the car will not run with full power or may not rev above an idle.

( and of course those naughty potatoes are known to quietly crawl inside the exhaust pipe when you're not looking too )

Nope, he pulled the cat and checked to make sure no pressure was building. We also disconnected the coil so no spark and cranked the engine, it does not even begin to go backwards with no spark.

Another simple test is put your hand over the exhaust as you crank it over. If you feel it suck, you have valve timing problems.

"Hey, your car SUCKS!"

Such tests assume that there are no exhaust leaks to work!!!

Done, and nope it blows it doesn't suck, until it starts going backwards, then it sucks. So my friends car sucks and blows.

It has to be a timing problem, either spark or valves.....or both!!

In reply to the reply to me and others. If this Audi 5 clyinder car has an Hall effect distributor advanced ignition system it has; a, engine timing marks on the flywheel b, a camshaft driven distributor so valve timing is synched to ignition timing unless something goes wrong but valve timing slip will mean ignition timing slip too c, No ballast resistor in circuit d, No computer, just an ignition module. Frank, Is the car equiped with K jetronic or L jetronic injection?

I will ask my friend about the type of injection. You are correct the distributor is driven off of the cam shaft. It does have a hall sensor in the distributor. The computer is somehow involved in this, since my friend can change the timing through a computer setting and we can verify the timing shifts correctly with this change with a timing gun.

I posed this question for people to ponder but somehow I think my post got lost or didn't post or something.

Do you think a working properly timed 4 cycle engine could be run backwards for a short time given that fuel is delivered from the exhaust side and the engine is cranked over backwards. Why or why not?

Is it possible? I suppose if everything backwards you could. I have read the previous post and all I can add to this is that the valve/ignition timing has got to be off. The only other thing I could think that possibly would be the problem is a twisted crank.

If you observe the engine cranking and see when it fires do you see the engine actually stop and reverse direction while holding the key in the start position? If not then the battery and starter are not the problem. You have a timing problem plain and simple. If it does reverse direction while holding the key in the start position, have the battery and starter checked.

i did once have a petrol engine on a forklift that ran backwards for about 5 seconds due to distributor being loose ( about 20 degrees out ) and the battery being half flat , not enough juice to crank over all the way , fired and ran backwards but i think the OP issue is totally different

Frank, no not in any normal circumstance. If the cylinders were flooded with fuel which was pumped in to the exhaust system and the timing was sufficiently out it is not impossible to imagine it may be able to suck it back in and run on it, but highly improbable. I am at a loss to know how your friend is changing the timing with a computer, this car is not equipped with one. Most pro timing lights can be made to retard the flash which than can be used to display the advance of the spark by aligning the retarded flash with the TDc mark on the flywheel or crank pulley. This isn't changing the timing, just retarding the strobe flash by a measured interval. Richard.

I'm all out of ideas frank. I really do want to know what it turned out to be when it's resolved though. Keep us posted.

I don't think that the engine timing has been fully checked in a proper manner.

Something like the following needs to be done:-

1) Remove engine top cover to expose camshaft/valve train.

2) Revolve engine (plugs removed) till both valves are closed on the Nr.1 cylinder and the piston is at TDC. This is the firing stroke. (if one valve is depressed, this is the exhaust stroke, turn farther!)

3) Check the position of the rotor, it should be at the position in the cap where the spark plug of cylinder 1 is connected.

4) Turn engine in the normal rotation direction, knowing the correct firing order (which I don't for a 5 cylinder!) make sure that the next cylinder that is at TDC is the next one in the firing order. Check that the rotor is at this cylinder's spark plug position.

5) This will happen/should happen for each cylinder one after the other. Check this carefully. Every 144° as the engine being a 4 stroke, must revolve twice for each cylinder, = 720° / 5 = 144° per cylinder........Use a gauge to make sure that each cylinder comes to TDC at about 144° apart and that the cylinder follows the firing order.

If it doesn't follow the order correctly, move the HT leads to the spark plugs to reflect the ascertained firing order.

Believe me, I have had this happen on a 4 cylinder engine. Once the plugs were correctly "leaded", the engine purred!!!

This needs to be done fully.....then you know that it is right or not.....

Something I just stumbled across, It may or may not apply.

CIS was developed by Bosch to replace mechanical fuel injection. While mechanical fuel injection is very efficient in supplying the engine with fuel, it takes horsepower to drive the pump. In some cases there is up to a 15 HP parasitic power loss. CIS does not have this downside, and is rugged and easy to maintain. It does, however, have some inherent drawbacks which must be taken into consideration. Air flow to the engine is restricted by the sensor plate. Excessive lift and duration camshafts and the inertia of the incoming air itself can cause poor throttle response due to the air sensor plate being bounced around. In addition, a phenomena called "charge robbing" can occur. This is caused by excessive exhaust overlap (i.e. the time span that both the exhaust and intake valves are open right before the intake cycle). This allows the exhaust gasses to flow backwards into the combustion chamber diluting the intake charge. For these reasons, camshaft selection should be carefully considered. Aggressive camshafts suitable for earlier model engines may not work well, if at all. Automatic transmissions and air conditioning also influence the type of camshaft used, due to the changing loads they place on the engine

Have you tried draining all of the gas and replacing with new? You may want to try disconnecting the fuel line and pull the gas for a portable can. I am just throwing stuff at ya, hopefully we can hit on something.

I am just about all done. Only one last suggestion; go back to basics.

Remove rocker cover and check the position of all the rockers ( valves ) vis a vis the lead position on the distributor cap. remove the plugs to do this. I think ANDY has detailed the way to do this.

Supply fresh fuel from a gravity fed can ( siphon ) straight into the inlet air stream, full throttle.

Supply spark from a working scrap yard coil, hot wired in.

If the engine fails to run, albeit roughly, it is down to valve timing as many have said.

P.S. beware of the backfire. Use gloves and goggles.

I give up on this. That last stuck valve post is just plain B*****it. Of course a starter motor can overcome the pressure of a closed cylinder ie valves stuck closed. That is what it's there for. And how doeas a valve stick closed on an overhead cam engine? If these people posting don't understand the first principles of an engine then why post?

Because they simply don't understand, that they "don't understand!"

You see it a lot on CR4......I just ignore it....as talking arguing with them is just wasting time and energy.....

It took me a long time to understand that it was not worth wasting my time and my energy.

yup

anything sensible has been said , its now up to the OP to complete diagnosis while " onsite " and then come back with the final verdict so we can add it to our collective diagnostic consciousness.

i hear what you're saying.

there is a phenomenon on this site sometimes where people come in , read a bit and then copy and repaste others posts as their own

do they think they are gonna get offered a job at NASA by doing crap like that ?

How is #116 a good answer? Is it possible to rate your self?

Not as far as I am aware, but I expect if someone really tries, its possible to give yourself a GA....it would also answer how he got the GAs in the first place.

As everyone (sorry, ALMOST everyone) knows, turning an engine over to start it requires that "pumped up" cylinders with both valves closed are required to be overcome......

Take an engine with the plug leads off, you can spin it with the starter motor very easily, even a diesel engine with its far higher compression....

If a valve was broken, the head of the valve would fall in the engine, or the camshaft would need to be damaged or similar. It was a fatuous comment.....

Is the cam driven with a belt, chain or gears?

If it's a belt, one look at it would tell the story. The rubber would be frayed and most likely pieces in the oil pan. If that's the case, the pick-up screen could be clogged with debris. May have to pull the pan also.

In all the engines I have worked on, the toothed rubber belt ones, the belt is always outside of the engine with a cover to keep inquisitive fingers safe, or faces if the belt actually breaks.....rubber and oil don't always agree with each other....

Only chain driven engines lube the chain in some manner....usually inside the engine....

I have not worked on a gear driven camshaft since around 1960 something......side valve (and the later to OHV conversions of an older style block) engines were sometimes gear driven....the cam was in the side of the engine above and to one side of the crankshaft.

As a side story not implying this is the Volvo's problem... I was driving at my normal 70 mph on an interstate here in US in a Shelby Omni GLH (1984). At that speed the motor died locked up, i pushed in the clutch and drifted to the side. I was an hour into a 6 hour trip with car very loaded with hunting gear, rifles, etc. I popped the hood took a quick look for external obvious stuff and all appeared ok so I assumed something internal had broke since it would not turn over and I was not in the position to do much. Had it towed home, jumped in a back-up and took off for the week. I had lots of family and friends advice but no one hit upon the final problem.

What I found on it was that the alternator bearings locked up solid. That car had the multi ribbed serpentine belt to drive the accessories and that alternator being frozen was enough to stop the motor turning 2200 rpms and then prevent the starter motor from turning the engine. I am still amazed how the alternator and belt connection created that much static grip to prevent the engine from turning. It was a 10.5/1 compression motor stepped up by Shelby. What I realized was I could have cut the accessory belt on the roadside and driven to a parts place and been back on the road after a quick alternator/belt replacement. If I only knew what to look for.

Because a little knowledge is a dangerous thing.

As stated above somewhere, the reason for the engine to run backwards is the last final spark from turning the engine off lighting the fuel in a cylinder and forcing the piston down. If that piston has not reached TDC, it can push the piston back down before it reaches TDC, Especially if you remember that you no longer have the starter motor for directional control.

A 5 cylinder engine has its firing pulses evenly divided by 720 degrees. That could help to bring the reverse running sequence into play.

I have seen a few cars that exhibited these symptoms, and they have all been healthy engines that did not have sufficient spark energy to start them while cranking, but did when the engine was returned to the run position. Fords with the first series of electronic ignition systems would refuse to start till the key was released. These were defective control modules. You say you changed the ignition modules already, so I would have to presume that two different parts would not fail in exactly the same way.

Substitute another ignition coil. Cheap and easy. Use any coil to test. As long as the primary voltage is correct, it should tell you something. The rotor, or cap could diminish the spark, but it should do it in start as well as in run. Try jumping the positive side of the coil to the battery. Another cheap test. Have you checked primary voltage at the coil positive while cranking?

Remember, compression is a result of valve timing and piston location being correct. That is an absolute. Happy hunting.

I'm sorry, I missed the line where you stated that you replaced the coil. For that reason, I would look at what is different when in start than when in run. Jump the coil positive to the battery. Use good jumpers and another battery to keep coil primary voltage high. Hell if I was that stuck, I would park a running car next to the dead player. Pull the spark plugs out of the good car, and run an extra long plug wire from the running car's coil to the patient's distributer. Connect both car's negative battery terminals with a jumper cable. (This jumper can be only 12-14 gauge wire, as it is only needed as a ground reference for the coil.) Get the Audi cranking over well, and then hit the starter on the "running" car. The distributer on the Audi should time the spark pulses pretty close, and send a quality spark to your Audi. Again, this test is only going to cost the price of a long coil wire. Good luck.

Still have not solved the problem, the next thing that we are going to check is the power going to the coil. As some have stated even when the spark looks healthy with the plugs out, it may not be healthy enough.

Anyhow here are some pictures of all the valve timing marks and the new coil and ignition module. In the picture with the chain there are two dots that align, they aren't easy to see with the oil on it. We did also check the distributor timing but I don't' have pictures, but I can assure you we checked it. As you can see my friend made an angle gauge aligned to the timing mark to confirm some of the other timings.

Nice pictures. Well done. Have you substituted a coil wire?

Were the position of both valves on cylinder 1 checked when the motor was at TDC as shown in the third picture?

A motor is at TDC twice for each completion of the 4 stroke cycle......

I have mentioned this check twice, one that must be made for each cylinder, in the turning/firing order, using a screwdriver to check the physical piston position at each cylinder, though you have never stated exactly whether it was carried out as I said....or not!

Sorry, but there is simply no good way to "jump over" this procedure......and be certain that it is correct....

All of the pictures were taken at the same time (with in a minute or so) with the motor at the same position, I simply can't take one picture that shows everything at once.

Yes a rod was placed in each cylinder to determine TDC, this is in the first comment I made to my post, but it was done.

You can also see the back side of the intake valves where the lifters press them, with the intake manifold removed so we can see when the valve its self moves. The owner of the car also turned the engine with a wrench and confirmed by pressure and listening when each valve opens and closes to make sure they were correct, this is the main reason for the angle marks.

This was not mentioned in your previous post, which is why I mentioned it again.

Nor have you stated categorically that each cylinder was tested, in the firing order, to see that not only was that cylinder at TDC on a firing stroke, but that both the valves for that cylinder were both closed and the distributor rotor was at the correct position for that plug lead in the distributor......

If for example the rotor has been replaced and the new one has the "tooth" in the wrong place (or the tooth is damaged or missing!), this will be the only way to discover this fact that I know of.......

I will be interested to hear about the final fix whatever it is........

As unlikely as it may seem that three guys who work on cars who have each changed timing belts and distributors on multiple cars without issue, we did actually correctly check all the timing stuff as one of the first things we did in trying to figure this out.

Categorically, yes, yes and yes.

Cylinder at TDC, both valves closed, distributor in the correct position for that cylinder, done for all five before I ever even posted the question to the forum.

More seriously tho, I do appreciate the comments, some suggestions are things that we haven't tried yet but did think of and it helps to know we aren't alone in our thinking.

As I said if I read this question myself from someone else and didn't see and test this engine in person, I would say check your timing, check your timing, check your timing.

All I can say is we checked the timing, but I know unless you did it yourself you probably don't trust we did it correctly, because from reading any forum post, I wouldn't either.

OK

I know it must be a little frustrating to have given symptoms and all the checking and rechecking that you (they) have done and to have people tell you to check the very thing you said had been checked multiple times. I think your timing is fine, and all the mechanicals are all fine. That leaves electrical and fuel. As for the fuel, I don't recall if you mentioned what type of fuel injection system you have, so what is the fuel system? Another way to tell if the plugs are firing is to slip an in-line spark tester (Harbor Freight carries them) and crank the motor. My guess is this will turn out to be fine, but worth ruling it out.

It is precisely because you have said before that the people working on this car are experienced that i have not elucidated fully the reasons behind my suggestions in earlier posts. I expected they/you would see the reasons for my suggestions.

Lay the plug outside the plug hole and crank over the engine.

If you get a belch of flame the ignition timing and the fuel injection timing are O.K. This means the plug is not firing under compression. If there is no flame the fuel injection timing or air:fuel mix is wrong.

This test is easy and i thought you would have seen the rationale and at least tried it.

If the plugs are not firing under pressure...

How about you try it first?

Jim

Don't want to make obvious comments but one can clearly see from the cam pictures that the firing order is 12453 yet the protractor fitted to tha crank pulley is marked 153... Have you got your plug leads back to front too?

Not sure of the crank configuration so in general terms - haven't you forgotten that the camshaft moves at half the rate of the crankshaft, and that with 5 cylinders (is it) in 720 deg, that the firing spacing is around 144 deg, so that the "first pass" over the "2" is not a fire position.

That is normal.

One needs to check the firing order at TDC with both valves closed on that cylinder.....what other cylinders are doing, with one valve open or not at TDC, can be safely ignored.....

I am reliably assured from the OP that this has been checked and the cam is correctly timed to TDC for each cylinder in turn (correct firing order) as is the rotor arm position for each cylinder in turn.....

I had a look around on the internet and surprisingly found only one firing order for 5 cylinder engines, is there more than one?

not actual anymore.

Trevor and Frank, please disregard my last Post. It was the sort of C**p I normally accuse others on this thread of talking. Trevor is correct; the firing order looks good. Richard

Hello. i became quite frustrated early in this thread due to the OP's failure to identify the vehicle .A major basic in diagnostics is to properly identify the vehicle.My experience with gasoline fueled engines cyclying backwards has been due to incorrect spark timing.Timing specs vary according to year,make,model,cid or cc,turbocharged or not etc.I have had part stores sell me the wrong ignition module and / or computer which caused a lot of wasted diagnostic time in thinking it must be something else.I have also had body repair shops change identifying decals along with body parts which also contributed to wasted time.I have also had people identify parts using the wrong terms (describe an idle stabilizer or impedance transformer as a computer).So i am reluctant to give more of my time when simply poking around in the dark.

Frank,

Is this engine equipped with a magnetic pick-up on the flywheel or crankshaft?

I'm thinking that the distributer has a hall sensor but the ignition module needs to reference the crankshaft position too. When there is a mag pick-up on a flywheel, some times the metal shards from normal cranking over the years sticks to the magnet and scrambles the signal from the pick-up. Check the manual and see if it has a crank trigger.

The problem was solved, I made a separate post with what it turned out to be

http://cr4.globalspec.com/thread/73164/