Alfa Romeo Forums banner

1 - 20 of 38 Posts

·
Registered
Joined
·
2,513 Posts
Discussion Starter #1 (Edited)
:confused:How in the world would a fuel injected car diesel after the ignition key being turned off??? Wondering if this would lead to the other question of why my rev limit keeps kicking on too soon. I know on carbed engines this occurs from alot of heat in the cylinders and compression, burning fuel entering through the carbs, but never, ever heard a electronic fuel injected car diesel before! Unless, the fuel injectors are begining to leak, I know the pressure to them takes a little while to die off, Hmm...
 

·
But Mad North-Northwest
Joined
·
10,063 Posts
There's only two ways I can think of for a Motronic to run-on after shut off: a fried ignition switch or leaky injectors (probably also coupled with carbon build-up in the cylinder causing hot spots).

If it's just the engine running and not the accessories as well than it's likely your injectors are dirty and not closing fully. That could also explain your problems at high RPM.
 

·
Registered
Joined
·
2,513 Posts
Discussion Starter #3 (Edited)
There's only two ways I can think of for a Motronic to run-on after shut off: a fried ignition switch or leaky injectors (probably also coupled with carbon build-up in the cylinder causing hot spots).

If it's just the engine running and not the accessories as well than it's likely your injectors are dirty and not closing fully. That could also explain your problems at high RPM.
My pistons are clean, **** near bare aluminum clean. The problem at high rpm are more comparable to a rev limit problem and a lean running condition problem. I can accelerate faster at half throttle, faster than say full throttle, I've talked to papajam over this one and he agreed it seemed as though I had a lean problem, but the dieseling, does seem as you say...I'm very confused about where to go from here with dealing with this car...too many problems at once I suppose.
You nailed it right with the accessories not running as that would've indicated a bad ignition switch causing power to run those, but no, everything else shut off as they should've. We have the same ideas about the injectors, I would imagine the only true way to test this is from removal and testing of the injectors.
 

·
Registered
Joined
·
2,984 Posts
if you are going lean that can melt things. there mght be somthing that started to melt and changed shape and now it stays hot. and if it is dieseling my guess it is knocking all over the place. if the ECU has a knock sender it must be maxed out.

I would start with a meter and check the voltage on shutdown. if all look good then pull the injectors out keeping them attached to the gas line and turn the key and hold open the flap to start the gas pump.(If not the flap then hot wire the pump) check for any leaks.

look at the plugs are any parts missing or any new parts welded to them?
also check the timming with a timming light. if the trigger wheel is off your timming could be way off. if all that checks out you might put on a gas PSI sender and check that the PSI if good under load when it starts to run bad.
 

·
Trained (ex)Professional, , 1953-2018 RIP,
Joined
·
16,232 Posts
Along the same lines as Stan's suggestion, I'd also use a noid light to check for injector pulse after shutdown.
 

·
Registered
Joined
·
520 Posts
maybe that damned aftermarket ignition bugged up your ECU. (u dont mention how this is the tip of the iceberg of stuff youve been dealing with lately).

Get a motronic ECU and see if it fixes it. if not send it back. 500$ isnt bad for a lesson on how much smarter Bosch is than you.

are you going to sell it on ebay? hows that auction going?
 

·
But Mad North-Northwest
Joined
·
10,063 Posts
Both easy enough to check and probably worth doing, but I can't see how it would possibly happen. Injector and plug triggering are directly controlled by the Motronic ECU. When you cut the key, no power to the ECU hence no trigger. Unless (and I'm just thinking crazy out loud here) someone bypassed the Motronic relay or something goofy like that so the ECU was always seeing power, but then it wouldn't have just started happening.

Interesting problem indeed, and Mongo dunno.

I'm still just thinking clogged injectors. That could cause them to leak when closed and not spray enough fuel when open (possibly explaining the lean behavior at high RPMs).

[Edit: Whoa, if this is not stock Motronic then Mongo really dunno. Depends exactly what was done to the ignition system]
 

·
Registered
Joined
·
2,513 Posts
Discussion Starter #11
Both easy enough to check and probably worth doing, but I can't see how it would possibly happen. Injector and plug triggering are directly controlled by the Motronic ECU. When you cut the key, no power to the ECU hence no trigger. Unless (and I'm just thinking crazy out loud here) someone bypassed the Motronic relay or something goofy like that so the ECU was always seeing power, but then it wouldn't have just started happening.

Interesting problem indeed, and Mongo dunno.

I'm still just thinking clogged injectors. That could cause them to leak when closed and not spray enough fuel when open (possibly explaining the lean behavior at high RPMs).

[Edit: Whoa, if this is not stock Motronic then Mongo really dunno. Depends exactly what was done to the ignition system]
My car is fried!!!!! I need to take the plugs out and check them out, also maybe do a ohm reading on the plug wires to be sure, I can not get past 3K rpm now, once she is on the highway, 2.5K rpm. At work I broke out the acetylne torch and cut a hole in just in front of the cat, so that I could eliminate a clogged cat being the problem. I can now say my car runs poorly and is now too loud. The dieseling only occured once and has not returned, I poured in fuel system cleaner, used sea foam through a vacuum line, etc... so that MIGHT have taken care of that problem, but the only thing after market on my ignition is the MSD coil, that is it, Bosch is every where else (I did order in a Jacobs Electronics Pro Street Kit:D) I am having severe problems and it seems only to get worse by the day and worst from start up to engine warmed up. But even cold start in the morning, It won't get past 4K rpm, so a problem is in there somewhere.
 

·
Premium Member
Joined
·
801 Posts
What you are saying is that with all the new goodies on it, it has run fine in the past but recently developed the 4K ceiling.
You know all the things to check: Air leaks developing as the engine moves as it revs.
Check timing with a light and make sure the advance is working well. Too much advance will cause a rev ceiling.
As far as injecters the cold start could be leaking.
 

·
Registered
Joined
·
2,513 Posts
Discussion Starter #13
What you are saying is that with all the new goodies on it, it has run fine in the past but recently developed the 4K ceiling.
You know all the things to check: Air leaks developing as the engine moves as it revs.
Check timing with a light and make sure the advance is working well. Too much advance will cause a rev ceiling.
As far as injecters the cold start could be leaking.
Thank you, will be checking all of that and more today, calling off work to get her done, also going to make a mod to the thermostat, but am too going to get everything underhood checked out systematically.
 

·
Registered
Joined
·
2,513 Posts
Discussion Starter #14
Crankshaft pulley is wobbling all over the place:( The nut securing it is tight, so either this pulley that I just bought is warped or the crank shaft snout is warped...
 

·
Administrator
Joined
·
16,621 Posts
I beleive your car is 'Motronic' thus should have the crank sensor that reads off the pulley (unless that is something you've modified...).

It is an unfortunately common occurance for the hub of the pulley to crack at the keyway. If that is what happened and a piece of the hub is loose/missing, that'd explain why the pulley wobbles.
 

·
Registered
Joined
·
520 Posts
heh sorry - ya i was just poking fun. im a bosch-purist and work my *** off to find original parts (whereas douglas is the anti-bosch). so is it possible that this could also be something as easy as a small mistake in reinstallation of your ignition? turning the key off shuts down the ignition.

still tho, motronic doesnt have an independant fuel pump (u dont hear anything behind you when you turn the key like a fuel pump priming) so where can it find the fuel to diesel-on? vapor?

if i were you , i would be on the lookout for a salvage S4 to be able to test sensors off of and do some elimination.

what mod to the thermostat u crazy bastard? i just replaced mine and am still having odd heat issues. are u? whats the plan there for ya?
 

·
Registered
Joined
·
520 Posts
It is an unfortunately common occurance for the hub of the pulley to crack at the keyway. If that is what happened and a piece of the hub is loose/missing, that'd explain why the pulley wobbles.
how does this occur. how can it be avoided? is it from belts being too tight?
 

·
Administrator
Joined
·
16,621 Posts
how does this occur. how can it be avoided? is it from belts being too tight?
I suspect it is due to the keyway cut into the pulley's hub. That makes a weak point - and the sharp corners of the cut make it worse.

Have a look at the pictures in replies #18 & #20 in this thread.
 

·
Registered
Joined
·
2,513 Posts
Discussion Starter #20
I beleive your car is 'Motronic' thus should have the crank sensor that reads off the pulley (unless that is something you've modified...).

It is an unfortunately common occurance for the hub of the pulley to crack at the keyway. If that is what happened and a piece of the hub is loose/missing, that'd explain why the pulley wobbles.
I bought this replace the pulley that broke in half along the keyway and chewed up my front seal. I'm wondering if my crank is bent, going to pull the pulley off (wow, say that 3 times real fast) and see if there is any damage to the pulley and use a dial indicator to see if maybe the crank is bent at the snout. The crankshaft sensor is more than likely going to have to be replaced-yet again! Urrrg!
 
1 - 20 of 38 Posts
Top