FE Build 1989 5.0 won't start when hot except when using starting fluid

JoeysAutos · Nov 5, 2020

Stock 302, starts up kinda reluctantly when cold, but is reliable. Just doesn't start up on all cylinders at first but then runs fine. Throttle response is poor when stabbing the throttle it stumbles for a second, but still drivable. If I leave the car running till it hits operating temp around 185f and shut if off for a few minutes, car just cranks and cranks and cranks with no signs of life. Spins just fine. Flooring it does nothing. Spray in a little starting fluid and she starts RIGHT up and runs fine. Otherwise will not start up again untill she gets below 160f and again does so reluctantly.

I've been chasing the reluctant starting problem for years but the hot start issue is newer. Just tested and got 30+ lbs of fuel pressure while cranking and running. New fuel pump+tank, new fuel filter, new plugs, wires, cap, rotor, coil, new TPS, new egr position sensor, new ECT, and I tried a different computer. No codes.

Just really at a loss here fellas.Ive scoured these forums and the whole internet for someone with this problem and I can't find anything. Would greatly appreciate any information.

General karthief · Nov 5, 2020

Well normally I would send you to the cranks but no start checklist,

Cranks OK, but No Start Checklist for Fuel Injected Mustangs

Cranks OK, but No Start Checklist for Fuel Injected 5.0 Mustangs model years 1986-1995 A word about this checklist before you start: it is arranged in a specific order to put the most likely failure items first. That will save you time, energy and money. Start at the top of the list and work...

www.stangnet.com

Don't jump around, start at the top and go step by step.
Ahhh, hell, who am I kidding, someone will tell you it's the pip in the distributor so go ahead and swap it out. You've replaced everything else, almost.

JoeysAutos · Nov 5, 2020

So according to that checklist the PIP can be tested with the use of a noid light, correct? If I don't get any flashes when the car is hot then the PIP is likely shot?

General karthief · Nov 5, 2020

Did you start at the beginning or did you jump right to the pip test?

JoeysAutos · Nov 5, 2020

Well yeah, I mean I've seen this checklist before so I've already done everything up till 5A which is the noid test. So I'm assuming that's how I should verify the PIP is bad before I proceed with taking my distributor out?

General karthief · Nov 5, 2020

Sure, gopher it if your confident it passed the other steps.

JoeysAutos · Dec 10, 2020

Alright now I'm really stumped. Did the noid light test, found the injector pulse to be basically non-existent for the most part. Figured that meant the PIP must be going out so I bought a new distributor with new TFI included. Slapped in the new distributor and there was no change whatsoever. Still have spark, still starts with starting fluid and runs great, but will not start once it's hot without using starting fluid.

With key on engine off I measured 12.00 volts exactly at the injector power wire. Tried both my junkyard and the stock computer and neither fixed the issue although the stock one runs a little better so I guess it's possible that both of my computer's are bad? Not sure, the checklist says that computer issues are rare, and I popped open the junkyard computer and it looks immaculate inside.

Overall I'm just becoming more and more mystified the more I try to fix this issue. I've been through the Cranks Ok No Start checklist about a hundred times now. Really really would appreciate any suggestions. This is making me want to light this car on fire.

General karthief · Dec 10, 2020

You've missed something, overlooked something, likely something simple,
The noid test is either a fail or pass, not a basically nothing for any part.
Do the steps one by one and report the results here, we'll help you out.

JoeysAutos · Dec 10, 2020

Okay, well in regards to the noid test, the light only flashed ONCE very weakly whenever I turn the key out of the start position to stop cranking the engine. I actually have a video of this happening on my phone. In terms of pass or fail I'm not quite sure what that qualifies as I guess. I assumed fail because my understanding was that if the noid isn't flashing while the engine is cranking that means no fuel is being delivered during startup which is kinda a huge fail to me. Never used a noid light before though so truly I don't know that for certain.

Noobz347 · Dec 10, 2020

Question:

Will the car start if you stomp the gas pedal all the way to the ground before cranking it?

Noobz347 · Dec 10, 2020

Additional test:

Prime the fuel pump (key-on / key-off) 3 times before cranking. Does it start?

JoeysAutos · Dec 10, 2020

Noobz347 said:
Question:

Will the car start if you stomp the gas pedal all the way to the ground before cranking it?

Sadly not. I will triple check this tomorrow but that has never worked in the 10-12 months I've had this problem.

JoeysAutos · Dec 10, 2020

Noobz347 said:
Additional test:

Prime the fuel pump (key-on / key-off) 3 times before cranking. Does it start?

Definitely not. I make sure to do this a lot, perhaps too often, to make sure the fuel rails are full. Probably helps a little with cold starts but does nothing with the hot starts which is the dilemma.

General karthief · Dec 10, 2020

Ok go back to the ignition switch under the dash, I believe there is a cranking ignition circuit and a run ignition circuit.
See #1 G on the list

JoeysAutos · Dec 10, 2020

General karthief said:
Ok go back to the ignition switch under the dash, I believe there is a cranking ignition circuit and a run ignition circuit.
See #1 G on the list

Okay, I looked at 1G and it just says to test at the coil for power on the red+lt grn wire. I did that just now and got 11.75 Volts with key in Run position.

I agree that there could be a problem at the ignition switch that causes the injectors not to fire while cranking yet allows them to fire while running but I really don't have any information on this subject to work with.

General karthief · Dec 10, 2020

Check for power at coil while cranking.

JoeysAutos · Dec 10, 2020

For the record, here is a complete list of my findings when going through the Cranks OK but No Start Checklist.

jrichker said:
Cranks OK, but No Start Checklist for Fuel Injected 5.0 Mustangs model years 1986-1995

A word about this checklist before you start: it is arranged in a specific order to put the most likely failure items first. That will save you time, energy and money. Start at the top of the list and work your way down. Jumping around will possibly cause you to miss just what you need to see to find and fix the problem. Don’t skip any steps because the next step depends on the last step working correctly.

Revised 26-Jul-2017 to add fuse link diagram.

All text applies to all models unless stated otherwise.

Note: 94-95 specific changes are in red

1.) Remove push on connector (small red/blue wire) from starter solenoid and turn ignition switch to the Run position. Place car in neutral or Park and set the parking brake. Remove the coil wire from distributor & and hold it 3/8” away from the engine block. Jumper the screw to the big bolt on the starter solenoid that has the battery wire connected to it. You should get a nice fat blue spark.
Most of the items are electrical in nature, so a test light, or even better, a voltmeter, is helpful to be sure they have power to them.

PASS - Has good spark at the coil in no-start condition.

jrichker said:
2.) Spark at coil wire, pull #1 plug wire off at the spark plug and check to see spark. No spark, possible failed items in order of their probability: [/b]
A.) Moisture inside distributor – remove cap, dry off & spray with WD40
B.) Distributor cap
C.) Rotor
D.) Spark Plug wires
E.) Coil weak or intermittent - you should see 3/8" fat blue spark with a good coil

PASS - Good spark on #1 plug wire.

jrichker said:
3.) Spark at spark plug, but no start.
Next, get a can of starting fluid (ether) from your local auto parts store: costs a $1.30 or so. Then pull the air duct off at the throttle body elbow, open the throttle, and spray the ether in it. Reconnect the air duct and try to start the car. Do not try to start the car without reconnecting the air duct.

Two reasons:
1.) If it backfires, the chance for a serious fire is increased.
2.) On Mass Air cars, the computer needs to measure the MAF flow once the engine starts.
If it starts then, you have a fuel management issue. Continue the checklist with emphasis of fuel related items that follow. If it doesn’t, then it is a computer or timing issue: see Step 4.

PASS - Starts right up with starting fluid.

jrichker said:
4.) No fuel pressure, possible failed items in order of their probability:
A.) Tripped inertia switch – Coupe & hatch cars hide it under the plastic trim covering the driver's side taillight. Use the voltmeter or test light to make sure you have power to both sides of the switch
B.) Fuel pump power relay – located under the driver’s seat in most stangs built before 92. On 92 and later model cars it is located below the Mass Air Flow meter. Look for 12 volts at the Pink/Black wire on the fuel pump relay.
C.) Clogged fuel filter
D.) Failed fuel pump
E.) 86-90 models only: Blown fuse link in wiring harness. Look for 12 volts at the Orange/Lt Blue wire on the fuel pump relay.
91-93 models only Blown fuse link in wiring harness. Look for 12 volts at the Pink/Black wire on the fuel pump relay.
The fuse links for all model years 86-93 live in the wiring harness near the starter solenoid.

94-95 models only: 20 amp fuel pump fuse in the engine compartment fuse box. Look for 12 volts at the Dark green/yellow wire on the constant control relay module.
F.) Engine seem to load up on fuel and may have black smoke at the tailpipe. Fuel pressure regulator failed. Remove the vacuum line from the regulator and inspect for fuel escaping while the pump is running. If fuel is coming out the vacuum port, the regulator has failed. Check the regulator vacuum line for fuel too. Disconnect it from the engine and blow air though it. If you find gas, the regulator has failed.

PASS - Fuel pressure verified with FP gauge. Steady 30+PSI while cranking and running.

jrichker said:
5.) Fuel pressure OK, the injectors are not firing.
A.) The PIP sensor in the distributor tells the computer when to fire the injectors. A failing PIP sensor will sometimes let the engine start if the SPOUT is removed.
A noid light available from any auto parts store, is one way to test the injector circuit to see if the injectors are firing. The noid light plugs into the fuel injector harness in place of any easily accessible injector. Plug it in and try to start the engine: it will flash if the injector is firing.

PASS/FAIL - "the light only flashed ONCE very weakly whenever I turn the key out of the start position to stop cranking the engine. I actually have a video of this happening on my phone. In terms of pass or fail I'm not quite sure what that qualifies as I guess. I assumed fail because my understanding was that if the noid isn't flashing while the engine is cranking that means no fuel is being delivered during startup which is kinda a huge fail to me. Never used a noid light before though so truly I don't know that for certain."

Currently has brand new PIP sensor + new TFI

jrichker said:
B.) Pull an injector wire connector off and look for 12 volts on the red wire when the ignition switch is on.

PASS - 12.00v EXACTLY at the red wire

jrichker said:
C.) No power, then look for problems with the 10 pin connecter (salt & pepper shakers at the rear of the upper manifold).

See the graphic for the 10 pin connector circuit layout.

The injector power pin is the VPWR pin in the black 10 pin connector.

D.) No power and the 10 pin connections are good: look for broken wiring between the orange/black wire on the EEC relay and the red wire for the 10 pin connectors.
E.) TPS voltage exceeds 3.7 volts with the throttle closed. This will shut off the injectors, since the computer uses this strategy to clear a flooded engine. Use a DVM, a pair of safety pins, and probe the black/white and green wires to measure the TPS voltage.
On a 94-95 Mustang, probe the black/white and grey/white wires to measure the TPS voltage.
It should be .5-.1.0 volts with the key on, engine not running. Note that if the black/white wire (signal ground) has a bad connection, you will get some strange readings. Make a second measurement using the battery post as the ground to eliminate any ground problems. If the readings are different by more than 5%, you may have a high resistance condition in the black/white signal ground circuit.

PASS - Brand new TPS adjusted to 0.79 volts. Backprobed TPS recently to double check, read the exact same voltage 0.79 volts.

jrichker said:
6.) Spark & fuel pressure OK.
A.) Failed IAB or improperly set base idle (no airflow to start engine). Press the throttle ¼ way down and try to start the car. See the "Surging Idle Checklist for help with all your idle/stall problems.

PASS - Brand new IAB, idle screw never adjusted, idles fine once running, and 1/4th throttle does not help when in no-start condition.

jrichker said:
B.) Failed computer (not very likely)

PASS? - Tried Junkyard computer and found no improvement. No codes.

jrichker said:
C.) Engine ignition or cam timing off: only likely if the engine has been worked on recently. If you removed the distributor, there is a good probability that you installed it 180 degrees out of time.

PASS - Runs fine once it's started. No engine work before the problem arose.

jrichker said:
D.) Firing order off: HO & 351 use a different firing order from the non HO engines.
HO & 351W 1-3-7-2-6-5-4-8
Non HO 1-5-4-2-6-3-7-8

PASS - Runs fine once it's started.

jrichker said:
E.) No start when hot - Press the throttle to the floor & try starting it, if you get this far. If it starts, replace the ECT.

PASS - Flooring it has no effect on no-start condition. ECT is new and Ohms Resistance tested for accuracy.

jrichker said:
F. ) Engine that has had the heads off or valves adjusted. Do a compression test to make sure the valves are not adjusted too tight. You should have a minimum of 90 PSI on a cold engine.

PASS - Valves never adjusted, had original valve cover gaskets until after this problem arose. Runs fine once it's started.

JoeysAutos · Dec 10, 2020

General karthief said:
Check for power at coil while cranking.

Just now I went ahead and stuck my test light in the red+lt grn wire's connector and it says lit while in run and cranking, never turns off till I turn it off at the key.

nickyb · Dec 10, 2020

It sounds like you've been beating your head over this for months.Your probably fed up,pissed to say the least.So just ease up on yourself and SLOWLY go over the list,every single step,step by step, just because the part was replaced does not mean it's good.I've learned this the f in hard way.Do not give up I know you can and will fix da fox.

General karthief · Dec 11, 2020

When you tested the coil when cranking power that was in the no start condition?
I know this is very frustrating, imagine on this side of it, I'm banging the kindle on my forehead screaming THIS SHOULD WORK!!! I feel that I could walk up to the car and look around, poke a test light around a few places and 'oh, here's the problem'.
And on your side of the interwebs you're doing the head slap thing and say'n 'I did that over and over and over again, same thing, IT DON'T WORK!!!!'.

FE Build 1989 5.0 won't start when hot except when using starting fluid

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