wizard124 wrote:I am starting to think I may have a bad Ignition Control Module.
The car never had the "engine just dies but starts up awhile later syndrome" I've been reading about. But it would do an occasional, brief engine miss/performance loss hiccup.
Thoughts?
Hiccups. The wires in the distributor can make hiccups when you get on it. The AFM potentiometer can cause hiccups at steady state RPMs at the revs the engine cruises at. The Temp sensor in the T can cause hiccups when you hit a bump, if the connection is bad. Distributor caps and wires can cause stumbling if the wires cross, or if the engine is damp. I have seen good caps go bad during rebuilds because they got cracked. You can get erosion of the wire from the coil to the cap inside the insulation which can severely limit spark delivery. Remember, all the injection timing and spark comes from the distributor pickup.
However, your problem seems to be either a restriction of air, a restriction of fuel, or a restriction of exhaust. I suppose you could be running super rich, but that doesn't seem to fit the symptoms. I assume there isn't a rag in the intake or a sticking flappy on the AFM. Your cam timing would have to be WAY out to make your car run like that. If you had a big hole in your intake trunk, your car would idle fine, but die when you got on it, if the flappy couldn't draw air and open.
If this was my car, I would have already replaced the fuel filter and cut the cat off of the downpipe. Not in that order though. I would also probably have pulled the top off the intake and removed the valve covers to look at where the cams are when the timing marks are all lined up. However, I think you are following a good path, to do the simple stuff first.
She is still running bad. These are the driving symptoms. If I throttle too quickly she bogs down. If I go easy, I can nurse it to about 3500 rpm but no higher.
To recap:
Fuel system. The pressure regulator tests good according to the Fiat manual. 35psi in the rail after cranking. Pump pressure maxes at about 38 psi with sufficient flow. New injectors substituted today; no change to running condition. Confirmed voltage at each injector plug and observed fluctuation during starter engagement.
Ignition system. Coil resistances within spec. Magnetic pickup specs good; wires not frayed. Swapped out Ignition Control Module; no change to running condition. Centrifugal and vacuum advance both check out. Spark at each wire. Twisting distributor doesn't clear the miss.
Engine. Compression at each cylinder maxes out at 170-174 psi. Cam alignment as close as possible. 17 inches of vacuum at idle (this may be low???) and nears zero when engine hits its rough rpm. Inspected snorkel, no cracks. I've pinched off the air line from the AAR, pinched off the fuel return line, pinched off the brake booster line, pinched off the CSV fuel line; nothing clears the miss.
AFM. plate moves freely. I cleaned the sliding contacts. Throttle plate. I checked the resistances and they are in spec. I hear the idle contacts when the throttle plate closes.
So, is the consensus my Cat or exhaust is plugged? That Cat was replaced about 18 months ago (maybe 3000 miles), That is why I am hesitant to look here. I suppose the older muffler components could have failed internally and plugged.
On a positive note, my rebuilt transmission shifts like a charm
Why don't you check your exhaust?????????????????? Don't look for consensus, you are the one with car in front of you.
Drill 1/8" hole, , stick vacuum/pressure gauge w nipple over hole, rev engine, see what pressure is. Takes me less than a minute. Then you KNOW. No broken bolts, no roaring exhaust. Take one minutes, and test your exhaust. Then you can move on the other things.
And like some others posted, this is hard to understand, so sitting still, hand on throttle, you open throttle wide open, and car won't rev?? And vacuum goes to zero??
PLUGGED CONVERTER
A partially plugged converter will create a restriction in the exhaust system. This, in turn, will cause an increase in exhaust backpressure that can strangle engine performance, particularly at highway speeds. The engine may start and idle normally, but lack high speed power. Fuel economy may also be down.
At first, you may suspect low fuel pressure or a plugged fuel filter (which can cause similar symptoms). A simple fuel pressure check with a gauge will tell you if idle pressure is within specifications, and a flow test will tell you if the fuel pump is capable of delivering enough fuel volume to meet the engine’s demands. You may also replace the fuel filter in an effort to cure your customer’s problem. But when the problem persists, it’s obviously not fuel-related. More likely, it’s an exhaust restriction.
An exhaust restriction created by a partially plugged converter can also backup heat in the engine, causing the engine to run hot and possibly overheat. If this is the case, you may suspect a cooling system problem. A low coolant level, coolant leak (internal or external), stuck thermostat, defective cooling fan, clogged radiator, kinked radiator hose or bad water pump can all make an engine run hot and overheat. So if you’ve checked all of these things and found no problem, you may be scratching your head wondering what’s going on?
The fact is, many technicians don’t consider the converter as a possible cause of engine performance problems or overheating until they’ve exhausted all the other possibilities. So maybe a better diagnostic approach would be to check the converter first when an engine is exhibiting symptoms that may be due to a converter restriction.
One of the quickest and easiest tests to perform is to check intake vacuum with a vacuum gauge. Find a place to connect a vacuum gauge to the intake manifold, and start the engine. Intake vacuum should usually be 18 to 22 inches of mercury (Hg) and remain steady at idle. If the vacuum reading is low and continues to drop, the converter may be causing a restriction.
Next, increase engine speed to 2,500 rpm and hold steady. The vacuum gauge needle will drop when you first open the throttle, then stabilize. But if the vacuum reading remains low or continues to drop, backpressure is building up in the exhaust system.
Disconnect the converter and recheck the intake vacuum reading. If the reading goes back to normal, you’ve identified an exhaust restriction that needs further diagnosis before you condemn the converter. Though a plugged converter would be the most likely cause of the restriction, it’s also possible the exhaust system may have a collapsed or pinched exhaust pipe, or the muffler may be clogged.
An alternative to measuring intake vacuum is to measure exhaust backpressure. It’s a much more difficult check to make because you have to find a place in the exhaust system to attach a gauge. If the engine has air injection, you can disconnect the check valve from the distribution manifold to hook up a gauge. Or, if you really want to make a lot of extra work for yourself, you can remove the oxygen sensor and take your reading at its hole in the manifold or headpipe. Refer to the backpressure specs for the application. Generally speaking, more than 1 psi of backpressure at idle, or more than 4 psi of backpressure with snap acceleration of the throttle is too much and indicates an exhaust restriction.
If the converter is completely plugged, it should be a no-brainer to diagnose. The engine will start, run for maybe a minute or so, then stall as exhaust backpressure builds up and strangles the flow of exhaust out of the engine.
If you suspect the converter is plugged, disconnect the converter and hold a trouble light up to one end. Then look in the other end. If you can’t see through the honeycomb, the converter is obstructed and needs to be replaced.
But before you replace the converter, keep in mind the possible reasons for it failing in the first place. Converter restrictions are often caused by severe overheating that damages the honeycomb. The underlying cause may be an overly rich fuel mixture or engine misfire (bad spark plug, plug wire or leaky exhaust valve). Any such problems should be diagnosed and repaired before you replace the converter, otherwise the new unit may suffer the same fate.
majicwrench wrote:Why don't you check your exhaust?????????????????? Don't look for consensus, you are the one with car in front of you.
Drill 1/8" hole, , stick vacuum/pressure gauge w nipple over hole, rev engine, see what pressure is. Takes me less than a minute. Then you KNOW. No broken bolts, no roaring exhaust. Take one minutes, and test your exhaust. Then you can move on the other things.
And like some others posted, this is hard to understand, so sitting still, hand on throttle, you open throttle wide open, and car won't rev?? And vacuum goes to zero??
I drilled the hole in front of the Cat.. No excess back pressure.
Very good. Now you know it is not exhaust.
Back to earlier question, if you hold full throttle vacuum falls to zero?? And engine won't rev past what?? Then just ?? dies?? runs rough?? blows up??
Vacuum WILL fall to zero as you snap throttle open, then should built again as engine revs.
I cant hit full throttle. I think it would die. If I go easy, i can hit 3500rpm, the miss and low vacuum go hand in hand.
I have the valve covers off, no obvious signs of damage. At TDC, the #4 cam lobes are opposite the tappets. Not perpendicular to the tappets however. Any visual guidance on this?
I pulled the connector at the ECU. Water temp sensor reads the same at the sensor and at the ECU. AFM readings do the same.
The AFM restistances read 50-100 ohms higher than spec. Temp sensor seems reasonable.
So, I am back to thinking it is the cam timing. The belt is the only thing I changed out that could be giving me this problem. All the FI wiring I have checked has shown no issues.
I think my plan is to disconnect the cooling T and pull the front cover. Start moving one wheel on tooth at a time and look for improvements in idle vacuum and running condition.
You will find that each time TDC comes around, you will see the cam lobes on cyls 1 and 4 alternate as to which ones are opposite the shim buckets.
Turn the engine to TDC #1, you can verify this looking at the cam lobes with the cam covers off as you have noticed.
After you have established that you are in fact on TDC #1, check your marks again.
Also lift the distributor cap and observe where the rotor is pointing. Trace your plug leads and make sure of their routing. I know this seems very basic, but you seem to have exhausted all other possibilities.
It is sometimes good to have a fresh set of eyes looking at things and I am still willing to make the trip.
Let me know.
instead of messing with the cam timing, first CHECK IT to make sue it is correct. and remove the valve covers too and check the lobes to see if they correlate with the cam line up pointers, if the don't then one of the upper wheels have slipped, or shifted, or broken the pin
Success. I am digging life, cruising top down in my Spider Good low end torque and a smooth shifting re-built transmission!
The first task I did this morning was re-set the cam wheels. I retarded just the intake cam by one tooth. This picked up the intake manifold vacuum at idle to 19 inches, when it was 17 inches before. But still no change with the mid-rpm miss. For visual reference (since my pulleys' holes won't align exactly with the marks on the cam housings), both holes are just slightly engine center of the casting marks.
With just about every component changed, or within tolerances. I had this in the back of my mind.
wizard124 wrote:
I pulled the connector at the ECU. Water temp sensor reads the same at the sensor and at the ECU. AFM readings do the same.
The AFM restistances read 50-100 ohms higher than spec. Temp sensor seems reasonable.
So, I decided to swap my AFM with an unknown spare I have.
Instant results. I'll write a post on my AFM diagnostics.
Warren
