81' 124 engine flounders after 5 minutes

[xaplax101]

hi there.......recently bought an 81 124 spider fuel injection.......set the valves and cleaned the engine bay......car starts and runs perfectly for about 5 minutes.......once the engine warms up it still idles as if all were well but the engine sputters and the power goes to zero and car stops driving.......it will still idle.....if I let it cool down for a few minutes it runs like a champ again for a few minutes and the cycle repeats......any ideas?
thanks
ted

[RRoller123]

Could be the coolant temperature sensor, located in the "T" at the front of the engine. Check connections. Take a reading at connection #13 back on the ECU, under the dash, passenger side. With the engine cold, and about 68-F outdoor temperature, the sensor should read between 2000 and 3000 ohms, measured terminal 13 on ECU to ground. With the engine and coolant fully warmed up (doesn't need to be actually running), the same reading should be between 250 and 400 ohms. In the Winter (very cold outdoors, and the engine cold), the reading will be between 7000 and 12000 ohms.

[76was124]

.......once the engine warms up it still idles as if all were well but the engine sputters and the power goes to zero and car stops driving.......it will still idle.....

Not sure I understand the above and what causes it to stall? Do you mean under load (driving)? Or just raising the idle?

Assumed you reset the timing, checked compression etc.

You could also check that the aav (auxillay air valve) is closing after warm up by pinching off the hose after it warms up. It pinching off causes a noticeable idle change, then its not closing correctly. Also I have seen cases where the aav housing leaks at the seams all the time, so improper idle is set when cold to compensate.

How did the car behave before the valve job?

[Odoyle]

Possible it could be a bad magnetic pickup, had the exact same symptoms and solved it with new pickup. Test the resistance across the magnetic pickup when engine is cold. When the engine quits, recheck the resistance, in my case resistance was increasing when engine heated up, which it should not.

[GeorgeT]

First you need to get the Bosch Fuel Injection Troubleshooting Guide (available online). As mentioned before check the Coolant Temperature Sensor, then check the Ignition Control Module and then check the injectors for power (if there is no power to the injectors after running a while the Dual Relay may be failing, ask me how I know).

[rridge]

If you have no reason to suspect fuel or spark, rule out the ignition first. It is the simpler system and some would argue the less reliable one. Also, F.I. is triggered by the signal it gets from the ignition.

When the engine stops be prepared to test it right then. A failing ignition module will cool off in five minutes and the symptom may disappear. It's not a tough test. Either you have a fat spark or you don't. Use a spare plug in the end of one of the ignition wires and an assistant in the driver's seat or a remote starter. The plug can be grounded on any cad plated bracket screwed into the sheet metal. I use the number 4 plug and the hood latch housing on the firewall.

[xaplax101]

Possible it could be a bad magnetic pickup, had the exact same symptoms and solved it with new pickup. Test the resistance across the magnetic pickup when engine is cold. When the engine quits, recheck the resistance, in my case resistance was increasing when engine heated up, which it should not.

thank you for the response.......what magnetic pickup are you referring to?
thanks

[xaplax101]

thank you for all of the responses............I started it again today and noticed that the gauge temperature would jump from 160 to 260 (which is pretty much pegged) ......does that information get communicated to any of the other controlling devices and influence their behavior?
best
ted

[courtenay]

thank you for all of the responses............I started it again today and noticed that the gauge temperature would jump from 160 to 260 (which is pretty much pegged) ......does that information get communicated to any of the other controlling devices and influence their behavior?
best
ted

No. You can disconnect the wire leading to the sensor that pegs the needle. It’s probably pooched. It the one closest to the front of the engine block...between the valve covers

[Odoyle]

Magnetic pickup is a white wire on the exhaust side connecting the coil to the distributor.

[76was124]

I started it again today and noticed that the gauge temperature would jump from 160 to 260 (which is pretty much pegged)

Does it bounce around, or peg immediately or after running a bit?

Are you sure you aren't overheating? Water pump issue, or Air in the coolant system?

Failed cooling, or oil pump failure, or a blown head gasket can all cause an engine stall and eventually seize!

[xaplax101]

wow, what a great forum this is. this is the first time I've posted here and the answers and suggestions were really impressive...........to answer some of the questions posted in the replies.....spark and fuel are good.....I replaced the coil because I had a coil on another car that would misbehave when the engine heated up but in this case it didn't solve the problem....there is 0.5 micro farad, 360VL condenser attached to the coil.........I couldn't find a replacement for that at the local auto stores or at autorecambi......any ideas on where I can find one? (I had a car where the condenser also created erratic behavior). when idling I noticed that if I disconnect the throttle position sensor (that black plastic Bosch thing on the intake manifold) it emulates the failure mode so I ordered one of those as well as all of the temp sensors for the engine........

I'll describe the symptoms further....the temp gauge on the dash is erratic.....it goes from 160 to being pegged at the hot end of the scale over and over again.......it clearly has nothing to do w the actual engine temp......the car runs great for a few minutes and then transitions into a mode where it idles smoothly but when you step on the gas the engine starts to die after about 1500 RPM and then suddenly comes back to life then dies and repeats the pattern......it lurches along at about 5mph....I did not see a temp sender unit on autorecambi that looked like the one the T in front of the engine. there are 2 probes in the head between the spark plugs.......what do those do? the manuals that I have for the car aren't very good

to recap.....I ordered the following parts from autorecambi

Throttle Position Switch - 1980-85
Ignition Control Module IG3-464 1
Gauge Temperature Sender CO8-000 1
Gauge Temperature Switch

if there are any other parts under suspicion please let me know.......im amazed at how inexpensive parts are for this car
thanks again
best
ted

[18Fiatsandcounting]

Ted, a few thoughts:

On the capacitor (condensor), these used to be used to reduce any arcing across the ignition points, but since you have electronic ignition, the likely function is noise suppression for the radio. Any electronic shop would have a 0.5 microFarad capacitor rated to at least 360 volts, and if RadioShack were still around, I'd steer you there. You can order capacitors online from places like DigiKey and Mouser, but they have literally tens of thousands of different capacitors so it gets hard to sort it all out, and you'll pay $10 to ship a 50 cent capacitor. Try an electronics shop where you are. Note that it doesn't have to be exactly 0.5 uF, and in fact capacitors have such wide tolerances that anything from 0.4 to 1.0 would be fine. Any voltage over 360 volts is fine, too. 0.47 uF is a very common value, and that would work just fine. Don't buy an electrolytic capacitor, as they are polarized (plus and minus sides) and that's not what you want.

If the gauge flickers to full scale now and then, the most likely cause is that one of the temp sensors between the spark plug wells is going bad. To answer your question, one is for the temp gauge and one is an overtemp indicator to either send the gauge to full scale regardless of what the gauge is doing, or in some cases for a warning light. By disconnecting them in turn you can figure out which one is which. I've seen cars with these sensors in either order (front or rear), so you can't always be sure just by location. Note that the temp sensor on the coolant T is for something else.

As for the faltering at 1500 rpm, there are a gazillion possible causes, so we'd need to diagnose further. Could be plugged injectors, incorrect ignition timing, bad plug wires, a loose wire for a signal that the ECU needs, something wrong with an emission control item, etc.

-Bryan