Alfa Romeo Forum banner

1 - 20 of 23 Posts

·
Registered
Joined
·
69 Posts
Discussion Starter · #1 ·
Hi,

Running a 75 TS engine in a spider. It runs really well until you go over a bump then feels like it is going to cut out and 'kangaroos' all over the place. it always has done it since its had the engine from the 90's. The in tank pump is running as is the main fuel pump, new dizzy caps and rotor arms and spark plugs.

Ive tried tapping the fuel pump, main relays and AFM to simulate a bump but it runs perfectly.

Don't know if anyone has any ideas as to what it may be?

Thanks
 

·
Registered
Joined
·
1,839 Posts
It could be lots of things but I would be looking for something connected between the engine and the bodywork. The engine will bounce a bit on its mountings and could for example disturb a ground strap. Or, assuming you have the concertina hose from the air intake to the manifold I would take that off and carefully check for leaks. They often split and the split opens up as the engine moves, giving the symptoms you describe.
 

·
Registered
Joined
·
69 Posts
Discussion Starter · #3 ·
Thanks for your reply.

Have checked all the grounding on the car and found nothing untoward. The car definitely has no air leaks, checked everything is tight and recently had the manifold off the replace the hoses between the intake and the engine.

I'm now thinking maybe its something high tension electrical. Is there any way to test the coils and HT leads?

Its doing it worse than ever since I have changed the intake hoses, put new rotor arms and dizzy caps on and replaced the plugs.

Any other ideas. The car is quite unbearable to drive.

Thanks
 

·
Registered
Joined
·
1,839 Posts
Is there any pattern to the engine speed when it happens - at high revs or low revs?

The reason I ask is that there has been another thread on the VVT, the variable valve timing cam advance system. The way to test it is to apply power to the terminals when the engine is idling. If the VVT works then the engine goes very lumpy and sounds like it is going to stall.
I am wondering if there is a dodgy wire that stretches/rubs when you hit a bump and the VVT kicks in when it shouldn't? Obviously this is only a problem at low revs.

You could try disconnecting the VVT and testing the car. The engine will run OK , you will just lose some top end power.

The car will run OK even if the intank pump cuts out, but you would hear the main pump straining a bit when the tank is low so I don't think your problems lies there.
I don't know if the intank pump would be sufficient on its own if the main pump cut out. If it were my car I would start the engine and disconnect the main pump to find out, but I don't know if it would cause any damage so you might not want to try that!

I'm trying to think of anything else that would be disturbed and cause the problems when you go over a bump. My money would be on a stretched or semi-loose electrical connection but that could be in the engine bay or back with the ECU, or the ignition switch etc.
Given that it is a converted car the wiring for the ECU may be suspect as the ECU would have been changed.

Or, how about the crank sensor, which is mounted so that it is reading the gap in the teeth of the crank pulley? That has to be at a very close tolerance gap to the pulley. If it is a little loose in the bracket that could shift I guess. Its worth giving that a clean up anyway. There is mention of it in another thread here somewhere.

Good luck, it must be very frustrating!
 

·
Registered
Joined
·
69 Posts
Discussion Starter · #5 ·
Is there any pattern to the engine speed when it happens - at high revs or low revs?

The reason I ask is that there has been another thread on the VVT, the variable valve timing cam advance system. The way to test it is to apply power to the terminals when the engine is idling. If the VVT works then the engine goes very lumpy and sounds like it is going to stall.
I am wondering if there is a dodgy wire that stretches/rubs when you hit a bump and the VVT kicks in when it shouldn't? Obviously this is only a problem at low revs.

You could try disconnecting the VVT and testing the car. The engine will run OK , you will just lose some top end power.

The car will run OK even if the intank pump cuts out, but you would hear the main pump straining a bit when the tank is low so I don't think your problems lies there.
I don't know if the intank pump would be sufficient on its own if the main pump cut out. If it were my car I would start the engine and disconnect the main pump to find out, but I don't know if it would cause any damage so you might not want to try that!

I'm trying to think of anything else that would be disturbed and cause the problems when you go over a bump. My money would be on a stretched or semi-loose electrical connection but that could be in the engine bay or back with the ECU, or the ignition switch etc.
Given that it is a converted car the wiring for the ECU may be suspect as the ECU would have been changed.

Or, how about the crank sensor, which is mounted so that it is reading the gap in the teeth of the crank pulley? That has to be at a very close tolerance gap to the pulley. If it is a little loose in the bracket that could shift I guess. Its worth giving that a clean up anyway. There is mention of it in another thread here somewhere.

Good luck, it must be very frustrating!

Hi,

Thanks for your reply.

The problem is definitely worse at lower revs but if the bump is big enough it will still do it anyway. Just noticed the last few times it has been started it completely stalls. And if you blip the throttle quickly it goes to stall but just about recovers by revving up before settling back down to idle.

The fuel pump in tank is definitely good as it's new, the main pump runs fine even if you give it a knock it doesn't cut out.


The crank position sensor is definitely in tight and is now clean.

I can't find the plug to disconnect the VVT. Looked for arcing from the plug leads in the dark and can't see anything.

Don't know if you have any more ideas now it's nearly stalling when first started?

Thanks
 

·
Registered
Joined
·
69 Posts
Discussion Starter · #7 ·
Hi All,

Thanks for your replies. Sorry I haven't been on for a while, hectic with work. I've checked all the grounds and cleaned them up. Realised why the problem had suddenly got worse and tracked that down to one lead swapped round one position on one of the distributors so the problem is now back to before I changed the distributor caps. The problem is now confined to between 1500 and 2000 rpm. Still have to disconnect the VVT to see if it solves the issue. Will post back when I have done that.
 

·
Registered
Joined
·
69 Posts
Discussion Starter · #8 ·
Have finally got around to disconnecting the VVT it makes no difference at all with it connected or disconnected and you can hear the relay click in. I also tested it by hooking up 12v to the terminals and the car nearly stalled at idle.

Really am out of ideas. You can guarantee it will happen between approximately 1500 and 2000 rpm and it gets worse when you have been driving for a few hours.

Any ideas?
 

·
Registered
Joined
·
4,116 Posts
that means the VVT is working correctly.

Have you tried pulling/wiggling plug leads, coil wires etc when the engine is ticking over, to try replicate the symptoms? (use something well insulated, so you don't get knocked off your feet!)

Sticky AFM flap? recently a guy's spider would buck crazily unless he accelerated real slow and then it would smooth out in higher revs, also idled perfect.......we found the flap was sticking at a certain range........different problem, I know, but an easy check and worth lubricating in any case.
 

·
Registered
Joined
·
69 Posts
Discussion Starter · #10 ·
that means the VVT is working correctly.

Have you tried pulling/wiggling plug leads, coil wires etc when the engine is ticking over, to try replicate the symptoms? (use something well insulated, so you don't get knocked off your feet!)

Sticky AFM flap? recently a guy's spider would buck crazily unless he accelerated real slow and then it would smooth out in higher revs, also idled perfect.......we found the flap was sticking at a certain range........different problem, I know, but an easy check and worth lubricating in any case.
Hi,
Thanks for your reply.
Have tried wiggling all the wires I can find. Have had it running on separate coils and it is still the same so I don't think that is the problem. All the electrical connections seem tight.

Will check the flap on the AFM. I feel if I trace all the wires back I am not going to find the problem as it only does it in that rev range.

Thanks
 

·
Registered
Joined
·
4,116 Posts
oh and this thread had a twofold problem with his twinspark conversion, one was high idle, but the other was bucking @ 3500 rpm.......he got the idle fixed, but the cure for the bucking (last post) turned out to be the ecu.....any chance you could borrow an ecu anywhere to test?

Twin spark bucking at 3500 rpms - Alfa Romeo Bulletin Board & Forums

edit: oh and I read that the motronic coolant sensor (not the water temp. gauge sensor) can fail and send the ecu odd signals and make it run crazy....on my spider it looks just like an injector, but is blue.
 

·
Registered
Joined
·
69 Posts
Discussion Starter · #12 ·
Hi,

Sorry for taking ages to reply. I have been trying to fault find on the car. Have taken the coolant temperature sensor plug off and one of the wires was so far back in the plug it couldn't have been making contact with sensor itself.

SO that might be a possible cause for the problem. Anyway, I was going to push the wire back in and repair it so I peeled the rubber boot back on the plug and both wires have come out so I wonder if one of you would be kind enough to picture yours to show me which colour wire connects to which terminal if that makes sense or doesn't it matter?

My email is: [email protected]

Thanks
 

·
Registered
Joined
·
4,116 Posts
I would guess it does matter, as those bosch connector plugs are designed to fit on the sensors one way only.
I guess your TS is like the spider CTS (coolant temp. sensor): one black (to main ground) and one brown wire to pin#13 of the ECU.
but like you say which one goes where on the bosch plug connector!

Unfortunately to get to that plug on my spider is a major pita..........hopefully someone here has a part dismantled plenum so they can check for you.
 

·
Registered
Joined
·
69 Posts
Discussion Starter · #14 ·
Yes it is the same as your spider. I tried them both ways around. One way it ran absolutely awfully and stalled so I figured it was the other way and it seems to run fine.

About to take it out and test it. Really hoping this could be the problem!
 

·
Registered
Joined
·
4,116 Posts
here's hoping........the good thing is you actually found a problem.........with these sorts of intermittant problems, anything that you find to be "not quite right" is always a big plus:)
 

·
Registered
Joined
·
69 Posts
Discussion Starter · #16 ·
Unfortunately it is exactly the same :(

Have run it without the coolant temp sensor connected as well and its the same. Have also run without the lambda sensor and it is the same.

The flap on the AFM is completely free moving. Always springs back when you push it back. And if you disconnect that the car wont start so I assume that's ok. The only thing I can think is to check the relays get the switched 12v when driving by running a lead to the multimeter in the car.

Have had someone drive the car whilst holding the ECU to keep it steady on the bumps and it still does it so I'm not convinced its that.

Apart from checking the 12v when driving I'm totally out of ideas!
 

·
Registered
Joined
·
4,116 Posts
You can guarantee it will happen between approximately 1500 and 2000 rpm and it gets worse when you have been driving for a few hours.
so, is it not "bump" related anymore? or only at those revs AND a bump? (wierd!)

battery tight? ie. could the battery hold down be loose and over a bump it jumps, touches the terminal and shorts out for a second?

Ignition switch? when driving can you replicate the problem if you thump the switch;)

Crank sensor: I know you checked it is tight and clean, but can you wiggle the lead when idling (with care!!), and replicate the symptoms?
 

·
Registered
Joined
·
69 Posts
Discussion Starter · #18 ·
It does it in that rev range and over bumps at that rev range. When you get going you could go over any bump and it would be fine.

Bypassed the ignition switch and ran all the engine electrics direct from the battery. The battery is all tight too.

So far I have discounted the fuel pump and relay by running a direct feed to that and it's still the same. Coolant temp sensor discounted. All electrical feeds from the ignition switch and permanent lives taken direct from the battery. Tested the continuity between the pins on the ecu and connectors and that's seems fine. Have cleaned all the earths and they are good.

Wiggled all the wires including the one to the crank sensor and can't replicate it. Don't know where to go with it now!
 

·
Registered
Joined
·
69 Posts
Discussion Starter · #19 ·
Hi All,

Looking at some more stuff today.

I disconnected the crank angle sensor connector. The yellow wire goes to pin 25 of the ecu. One of the black wires goes to pin 23 which I assume is right.

With the ECU disconnected, there is continuity between the two black wires at the connector. I think the other black is a shield.

Is this correct? Its the only possible fault I have found!
 

·
Registered
Joined
·
69 Posts
Discussion Starter · #20 ·
Hi All,

Looking at some more stuff today.

I disconnected the crank angle sensor connector. The yellow wire goes to pin 25 of the ecu. One of the black wires goes to pin 23 which I assume is right.

With the ECU disconnected, there is continuity between the two black wires at the connector. I think the other black is a shield.

Is this correct? Its the only possible fault I have found!
Also, I have a blue and yellow wire going to the fuel pump relay and variator relay. Is this correct as it is not on my wiring diagram.

Thanks
 
1 - 20 of 23 Posts
Top