Help! Poor running only when hot!

[lgifford16]

I have a 1981 FI Spider that's become a supreme mechanical headache. After many previous issues to get the engine to start, warmup and run without stalling, we finally got the engine to start reliably, idle and warmup properly. We hoped that the engine issues were sorted. However, we took the car out several times today and it runs beautifully... for about a mile. After a mile or so, it basically goes into somthing akin to "limp" mode providing nearly no power, unable to rev to 2000 RPM in gear, and it starts to misfire. It acts as if it is very lean and faulters if the throttle is opened much beyond idle. This is completely a reproducible problem. It does not make sense that it is running out of fuel because during the high fuel demanding warmup period, it runs great. Once it gets to 120-140 degrees on the temperature gauge the drivability goes south. However, it will idle just fine after the high speed drivability goes away.

Observations:
Warmup drivability in perfect.
Temp after a mile or so is ~130.
Idles perfectly both before and after "limp" mode has started.
Disconnected both temp gauges on top of the motor and had the exact same problem.

I am seeking ideas for the possible source of this engine problem. All I can imagine is an ECU problem because the problem seems to start once it goes into closed loop operation. I want to drive and enjoy this car! But after paying more to get it running than the car cost to buy, I still have no joy.

New parts (replaced in last 10 miles):
New starter
New ignition switch
Air snorkle hose is crack free and appears new.
new fuel filter
new battery
new fuel Injectors
new fuel Pressure Regulator
new AFM (not repaired)
New O2 sensor
new TPS
new silicon vacuum hoses
New Distributor cap
New Spark plug wires
New Spark plugs
New Fuel Pump
New ECU temp sensor (front of engine)
New Thermoswitch (on radiator)
New temp sensor (gauge)
New AAR
New air filter
New all fuel injector connectors
replaced engine wiring harness
New vacuum booster
grounds checked and contacts cleaned
New additional ground straps added to engine head and coil heat sink

[ORFORD2004]

I have a spare ECU

[So Cal Mark]

the temp senders on top of the head are merely for the gauge, the sender you need to be concerned with is the sender in the water outlet. You must check the resistance throughout the temp range to determine if that sensor is faulty. If the connector doesn't fit it tightly, you've gotta replace the connector

[lgifford16]

Mark - unfortunately that one has been replaced as well. However, what is the resistance supposed to be?

[GeorgeT]

You may want to check the pickup wire in the distributor. They will fray and at high rpms, when the timing advance weights are extended, you can get a short that will go away when the weights return to position.

[silverghost]

Does the distributor wire scenario make sense since the car runs fine when cooler? It sounds like a lean out issue when the motor actually requires less fuel. I've seen this car and it back fires through the intake when it warms up and will not run under load above 1500 RPM but it will rev to red line with no load once it is hot. BTW, it revs freely to red line prior to warming up. Yes, I know this is a bad thing to do!

[lgifford16]

'Nother update!

Replaced the rotor inside the distributor cap - I do have a question though about how that attaches to the ignition control module.

Also replaced the ECU.

No changes what-so-ever.

I'm about to give up! Help!

[narfire]

Where do you hang your hat? Anyone nearby? If you are in the south Okanagan BC, I can give you a hand and see if we could sort it out.

[lgifford16]

Thanks for the wonderful offer!

Unfortunately I'm currently in Arizona, and am in the process of moving up to Iowa.

[So Cal Mark]

I see a list of parts that were replaced, but were they tested and confirmed bad before replacing? I'd like to know what the fuel pressure is, especially when it's running poorly. Is the catalyst still in place? What is the O2 voltage when there is no power?

[lgifford16]

A majority of the part replaced were confirmed bad (by resistance, or lack of function etc)
Some of the sensors were replaced because we didn't know how old they were (O2 sensor, temp sensors, etc)

Yes, the car has it's catalyst in place, I'm going to go get a fuel pressure tester to check on that one, and will also look at the O2 sensor voltage. Thanks for those suggestions!

[lgifford16]

Thanks for all your help Mark!

Got a fuel pressure tester, and replaced the fuel pump with a known good one. Fixed the issue completely.

[So Cal Mark]

great news!