wont start unless tb blocked PLEASE HELP!!!

Wierd.... and the throttle is closed right? Check your TPS sensor and IAC. Sounds maby like you not getting fuel or something, so you restrict it enough to get a combustible mix?

Wierd.... and the throttle is closed right? Check your TPS sensor and IAC. Sounds maby like you not getting fuel or something, so you restrict it enough to get a combustible mix?

Click to expand...

I too would check the air bypass valve on the front of the thottle body they do get carbon build up on the inside, and do go bad once in a while. They are not cheap to replace. They will run you about 80$new.

I also take it your car is non-mass air equiped (pre 89) if you are covering the thottle body with your hand.

Didn't you buy a 90GT? I'm surprised you got it to run at all with the MAF disconnected from the engine...?

You pulled all the codes from it right? I'm inclined to agree with the first two replies...ck your IAC, and TPS.

it sounds more serious than just the IAC though...i have seen engines run with no IAC, albeit with high idle. possibly the intake has bad gaskets...or youre not getting enough fuel pressure.

ahh, so you have a no run when warm problem. i missed that last post the first time. it is possible that you have a bad fuel pump...mine did this, but only once (we only had one 60+ degree day here in the fall/winter). so do this:
1. check your fuel pressure with a gauge
2. if fp is ok, try another tfi module
3. if fp is not ok, then check the pump.

after the car spudders out and dies, go check the fuel pressure at the shraeder valve. see if any fuel spits out, no fuel = bad pump or clogged fuel filter or a possible faulty fuel pressure regulator. just my thoughts.

something is causing you to lose vacuum...you make more vacuum when you cover the tb. try using a vacuum gauge. on the old carbureted cars, the choke would do what you are doing with your hand. it cut off some air, increasing vacuum and drawing in more fuel (which was needed when the engine was cold).

i'd check your fuel pressure to see if it doesnt puke out after it dies. if your fuel pressure stays the same then it isnt fuel related. you mentioned in another thread where your ACT and Coolant Temp sensors were throwing codes? i had a 90 probe 4 banger, both the ACT and the Coolant Temp sensors were shot and the car wouldnt start at all till i replaced them. just a thought.

or if the outside temp is too hot/cold (out of self test range)

superhuaman said:

or if the outside temp is too hot/cold (out of self test range)

Click to expand...

yep, when the engine is cold, most likely it wont start if those sensors are bad. if it does it'll do brief starts like the 2 sec. run mentioned. my probe did that also , started for 2-3 seconds then shut off , but after i replaced the sensor, once the engine was warmed up you could stick a 47ohm 1/2watt resistor in the plug to fool the computer that its running less than 160* to gain a few hp if any. once the engine cooled back down it wouldnt start until you plugged the harness back on the sensor. the main one that was causing the problem was the Coolant Temp sensor.

it could be the Coolant Temp sensor or the ACT sensor in your case, or might even be both. they arent cheap, last time i bought one for the 89 the coolant sensor was around 40 bucks.

they disconnect from a plug, you have to use a wrench or socket to remove the actual sensors.


the Coolant Temp sensor is on the coolant rail right below the throttle body, its the sensor behind the alternator on that black tube rail. the ACT sensor is on the drivers side of the lower intake manifold towards the front by the first 2 injectors. for the ACT sensor its not the one in the very very front, its the next one back, kinda sits under the upper plenum.

heres a couple pics to kinda get the idea of where they are.

ACT sensor


where i have this hose running is where the factory coolant rail is supposed to tap in at. the Coolant Temp sensor is on that rail. the rail extends from where that hose that i have pictured is back to your heater core hoses right under the throttle body.


hope this helps out a little.

See http://www.leemotorsports.com/f350/50enginepartsguide.JPG



Follow the checklist and you will find and fix the problem.
Cranks OK, but No Start Checklist for Fuel Injected Mustangs

Revised 18-Oct-2006 to include TFI fault during crank/run cycle
All text applies to
all models unless stated otherwise.

Note: 94-95 specific changes are in red

1.) Remove push on connector from starter solenoid and turn ignition switch on.
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.
No spark, possible failed items in order of their probability:
A.) MSD or Crane ignition box if so equipped
B.) Coil
C.) TFI module
D.) PIP sensor in distributor. See paragraph 3A - a noid light will tell if the pip is working by flashing
when the engine is cranking.
E.) No ECC or computer power - ECC or computer relay failure
86-93 models only:
ECC relay next to computer - look for 12 volts at the fuel injector red wires
94-95 models only: EEC or PCM power relay in the constant control relay module. Look for 12 volts at the fuel injector red wires.
F.) No ECC or computer power - fuse or fuse link failure
86-93 models only: Fuse links in wiring harness - look for 12 volts at the fuel injector red wires. All the fuse
links live in a bundle up near the starter solenoid.
94-95 models only: 20 amp EEC fuse in the engine compartment fuse box. Look for 12 volts at the fuel injector red wires.
G.) Ignition switch - look for 12 volts at the ignition coil red/lt green wire.
H.) Computer
J.) Engine fires briefly, but dies immediately when the key is released to the Run position. Crank the
engine & when it fires off, pull the small push on connector (red wire) off the starter relay (Looks
like it is stuck on a screw). Hold the switch in the crank position: if it continues to run there is a
problem with either the ignition switch or TFI module. Check for 12 volts at the red/green wire
on the coil with the switch in the Run position. Good 12 volts, then replace the TFI.

See the following links for wiring diagrams...

http://www.autozone.com/servlet/UiB..._us/0900823d/80/16/71/3c/0900823d8016713c.jsp for 79-88 model cars
Computer/fuel pump/ignition wiring diagram, 86 model http://www.autozone.com/images/cds/gif/large/0900823d80167158.gif
Computer/fuel pump/ignition wiring diagram, 87 model http://www.autozone.com/images/cds/gif/large/0900823d8016715e.gif
Computer/fuel pump/ignition wiring diagram, 88 model http://www.autozone.com/images/cds/gif/large/0900823d80167162.gif

http://www.autozone.com/servlet/UiB..._us/0900823d/80/19/59/5a/0900823d8019595a.jsp for 89-93 model cars
Computer/fuel pump/ignition wiring diagram, 89-90 cars http://www.autozone.com/images/cds/gif/large/0900823d8019595f.gif
Computer/fuel pump/ignition wiring diagram, 91-93 cars
http://www.autozone.com/images/cds/gif/large/0900823d80195960.gif

http://www.autozone.com/servlet/UiBroker?ForwardPage=/az/cds/en_us/0900823d/80/1d/db/3c/0900823d801ddb3c.jsp
for 94-98 model cars

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:
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

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.

Clue – listen for the fuel pump to prime when you first turn the ignition switch on.
It should run for 5-20 seconds and shut off. To trick the fuel pump into running, find the ECC
test connector and jump the connector in the Upper RH corner to ground.


If the relay & inertia switch are OK, you will have power to the pump. Check fuel pressure –
remove the cap from the schrader valve behind the alternator and depress the core. Fuel
should squirt out, catch it in a rag. Beware of fire hazard when you do this. In pinch you
can use a tire pressure gauge to measure the fuel pressure. It may not be completely accurate,
but you will have some clue as to how much pressure you have.

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.) 86-93 models only: Blown fuse link in wiring harness. Look for 12 volts at the Orange/Lt Blue
wire on the fuel pump relay. The fuse links 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.) Fuel pressure regulator failed. Remove the vacuum line from the regulator and inspect for fuel
escaping while the pump is running.

Fuel pressure OK, the injectors are not firing.

A.) A Noid light available from Autozone, is one way to test the injector wiring.
B.) I like to use an old injector with compressed air applied to the injector where the fuel
rail would normally connect. I hook the whole thing up, apply compressed air to the i
njector and stick it in a paper cup of soapy water. When the engine cranks with the ignition switch
on, if the injector fires, it makes bubbles. Cheap if you have the stuff laying around, and works good too.

a.) Pull an injector wire connector off and look for 12 volts on the red wire when the ignition switch is on.
b.) No power, then look for problems with the 10 pin connecter (salt & pepper shakers at
the rear of the upper manifold).
c.) No power and the 10 pin connections are good: look for broken wiring between the
orange/black wire on the ECC relay and the red wire for the 10 pin connectors.


4.) Spark & fuel pressure OK.

A.) Failed IAB (no airflow to start engine). Press the throttle ¼ way down and try to start the car.
B.) Failed computer (not very likely)
C.) Engine ignition or cam timing off: only likely if the engine has been worked on recently).
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
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.