[martrux]

I have a 1989 mustang Gt, I bought about 2 weeks ago. I like the car a lot, but I need to fix it! After running for a while, 15+ mins, it just won't restart immediately. I have to wait 2+ hours or longer in hot weather. When cold it fires in less than 1 second. When hot it cranks, fires once maybe, then never again for hours. i can push start it tho, as I've had to do several times now. Before this problem surfaced, I replaced the alternator, battery, and windshield wiper motor. A few days later this started happening. Now I've replaced the coolant temp sensor, air charge temp sensor, distributor, Ignition control module, coil, plugs, wires cap and rotor to no avail. I've tried jumping it even though it will crank by itself, and still nothing, just turns and turns, I can smell gas, and it's getting spark. I'm getting tired of throwing money at it and just curious if anyone has any ideas? Thanks

Completely unrelated, i had a check engine light but can't pull the codes due to my own stupidity, I have a new A9L coming this week.

 

[gj1981]

Does your car have LT headers at all? If it were me I'd have the starter checked. I'll ask this as a wild shot but the car is still fuel injected right?

 

[martrux]

yeah the car is still fuel injected, and I tried jumping it while the battery was still full to try to get more cranking amps just in case the starter was leeching. Would that work or should
i pull the starter and have it tested? Can they test it pulling to much power hot?

 

[Kyle F]

Most culprits to heat are the starter (usually won't turn when it gets too hot), the ignition control module (don't assume its good because you have a new one... get it tested), and the fuel pump(have you checked your rail pressure both hot/cold). Th einjectors could be giving you issues as well.

Are you having and driveability issues once it gets hot or does it only have a problem startign once you shut it off?

Also check your grounds.

 

[Kyle F]

yeah the car is still fuel injected, and I tried jumping it while the battery was still full to try to get more cranking amps just in case the starter was leeching. Would that work or should
i pull the starter and have it tested? Can they test it pulling to much power hot?

It will show too much cold vs a new one cold if this is your issue. However, since you are cranking, does it crank at the same speed war as cold? If its having a hard time and cranking slowly, the starter is probably your culprit.

 

[martrux]

I have a pretty hefty miss while running hot or cold, I thought it might be fuel pressure too, I'll get a guage later today. It cranks close to the same speed, sometimes it won't turn the first time for a second, then it will crank just as fast.

 

[Kyle F]

It cranks close to the same speed, sometimes it won't turn the first time for a second, then it will crank just as fast.

Check all you grounding ends and clean the inside loop of you battery connector and the negative battery post.

I know you have a new battery, but dont forget the cable and connection. This last line reminds me of so many problems I have solved by cleaning the battery terminals.

 

[128chris]

try replacing your fuel pump relay.

 

[martrux]

if my negative battery cable was... say... green under the insulation..... How bad is that?

 

[martrux]

update: I decided to test my TPS. It read 5.0 volts off of the green wire from the pigtail and the throttle body and just about any other ground. Now correct me if I'm wrong, but I read somewhere that 5.0 volts would be the same as WOT, which in a car that had been running would mean that the ECM was telling the car not to pump fuel into cylinders? This imo explains why the car would pop once like it was going to start, and if I caught it by pumping the gas would start up and run, albeit not very well, and if I missed it the car wouldnt fire again for hours until the ECM reset itself to defualt mode. Am I completely wrong here?

 

[FoxChassis]

You sure you are probing the Dark Green/Light Green wire and not the Orange/White wire? The O/W wire will have a reference voltage of 4-6 volts.

 

[martrux]

yes, and I checked 4 times.

 

[Kyle F]

Your TPS has nothing to do with starting the car. It stats by spraying a set amount of fuel into the cylinders as it pressures up the system, just like pumping the gas in a carb, but the computer takes care of it.

Now, I know GMs TPIs had the bypass mode that if you would hold the throttle at WOT, it would crank and not start. I am not sure if Ford did the same thing, but you could check your sensor Cold, and then Hot to compare the readings. If when cold you get a anythign less that 5, and Hot you get 5 or over... then try replacing the sensor. Actual settings ar about .95VDC closed - 5VDC WOT. Those numbers are ballpark, do not have to be dead on.

 

[martrux]

ok, so what sensor tells the car not to inject any gas when you push the gas pedal to the floor while cranking?

 

[FoxChassis]

Why are you opening the throttle completely (pushing the gas pedal to the floor) while cranking the engine?

 

[martrux]

I'm not pressing the throttle down, I'm referencing that i think my TPS or ECM is telling my injectors that it is being held down (the green wire on the TPS is reading 5.0V, and another thread says anything over 4.5V is telling the computer WOT).

 

[martrux]

My question was, hypothetically, what sensor would tell the computer to cut the fuel to the car if the throttle was placed to the floor while trying to start the car? Sorry for the confusion.

 

[dave1170]

I have the same problem martrux, when I test the green wire with the key on I get 4.96 as a reading. I thought my TPS sensor was bad so I bought a new one and it does the same thing! I've been told that I probably have a short somewhere in my TPS wiring harness. I would think this would cause a CEL though. Someone on another forum told me to return the new TPS and get another one, sometimes they are bad! Not sure if that is true or not, but I don't think the parts store will let me return an electrical part. I'll let you know what I find.

 

[Kyle F]

My question was, hypothetically, what sensor would tell the computer to cut the fuel to the car if the throttle was placed to the floor while trying to start the car? Sorry for the confusion.

If the Ford ECM has the same programming as the GMcomputer, it would be the TPS reading that the Throttle was all the way in.

Yes sometimes the stuff you buy at the Autoparts store is bad from the get go.

 

[5.0VOLVO]

hard starting when hot can also be a symptom of a coolant temp sensor going bad.