98 mustang gt won’t start

Cadehall234

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Oct 19, 2019
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I have a 98 mustang gt automatic that won’t start. I just installed an Edelbrock victor jr intake along with edelbrock high flow fuel rails, edelbrock low profile upper intake plenum and a 90mm accufab throttle body. The theft light had been coming on before I tore it apart but is now blinking. The car started a few times was very hard starting and when it did start it had a very irregular idle like it was cammed and it smoked a lot on the first few start ups. The next day I cannot get the car to start at all it acted like it wanted to start but was boggy and being choked out. The exhaust smells strong of gas so I know that it is getting fuel. I scanned it with my scanner tool and and got o2 sensor codes so I checked and come to find out the o2 sensors have been removed and the plugs are zip tied up. But I didn’t think that was why it wasn’t starting, so I went into the active test on my scanner tool and looked everything over. The fuel tank pressure value is reading 5 which is very high I have not checked my fuel tank pressure sensor yet because I believe it is on top of the tank and I didn’t want to drop it but I plan on checking it tomorrow. My short term fuel trim is at 94 and my reference voltage value is a red 0. If I try to crank it the motor is turning over and acting choked out and will occasionally pop out of the throttle body. I have taken the gas cap off and the fuel tank pressure did not change, I have checked all of my fuses and plug connections to the engine with a multimeter. Yes the tps is getting proper voltage readings along with the iac and maf. Also when cranking the motor over sometimes the fan will click on and then off. I’m not sure if the pcm is bad or if I have a short but I’m assuming the 0 value on the reference voltage is the main cause. Sorry if I’m providing a lack of information I’m new to this and I’m doing my best, thanks in advance to any help.
 
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wmburns

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Aug 14, 2009
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Did you connect the fuel pressure regulator intake vacuum reference line? And is it leak free? What is the fuel pressure?

Always best to post the full DTC codes. There are 1,000's and they each have a story to tell.

Was the PCM "bad" before you started working? IMO it may be more reasonable the system voltage is dropping too low causing the CCRM to "drop out". Is the battery fully charged? What about the condition of the grounds around the radiator core support? To the PCM voltage is like oxygen. Just like a human, not enough oxygen (voltage) will cause a "black out".

Howto perform charging system voltage drop test

A bad fuel tank pressure sensor (FTP) will not cause a no start condition. It will cause EVAP related DTC codes.

Suggest that you CONFIRM that each fuel injector is actually pulsing. Use a "noid" style test light. What I'm wondering is IF one of the fuel injector signal return lines is grounded. If true this would dump fuel into the intake.

Have you also confirmed spark? What about the spark plug wires? Are you sure that you have run the correct coil pack wires to the correct cylinder? I could see incorrectly routed spark plug wires looking like a timing problem.

Back fire can also be a symptom of a base engine timing problem (timing slip). For some engines it can also be a symptom of a CMP or CKP sensor problem. The 4.6 doesn't use the CMP sensor in the same way as the V6 does.

V8 coil pack diagram

Where and HOW did you measure the 5 volt reference? This is a Ford and not a GM. Ford doesn't use a 5 volt reference everywhere like GM does. The 5 volt reference should be measured using the GY/RD wire as the ground reference.


1996+ Crank with no start check list
 
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Cadehall234

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Oct 19, 2019
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Is it possible I’m experiencing this no start condition because I don’t have a tune? It is a victor jr intake with a 90mm plenum and 90mm throttle body on a bone stock motor. (I know it sounds dumb to go that big but as soon as snow falls it’s getting heads and a cam and I needed a new intake so I figured why not)
 

wmburns

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If looking for an educated guess I would so no. Why? Because the motor uses a MAF sensor that actually measures the air going into the motor. Having a larger intake isn't really going to have an impact as long as the MAF is reading correctly. Besides what is the diameter of the tube where the MAF is actually installed? Is it stock? For your theory to hold, the MAF would have to be over stating the amount of air entering the motor.

Do you want another way to think about your theory? Let's say that the theory is true that the larger intake is allowing sooooooo much air to enter that this was upsetting the tune. Then it would be expected to have a LEAN AF mixture? Clearly your motor is running RICH.

Do you have an ODB2 scanner? Because if you did likely you could definitely answer this question in a few minutes by looking at the MAF value. Plus the ODB2 scanner would give access to TONS more information that may prove vital to solving your problem. Plus it will be yours use to use in the future.

Just wondering. Did you read all of the information in the links provided? Especially the crank with no start check list? What happened when the MAF sensor disconnected?

I a big believer in Occam's razor . If following that logic I'm afraid that the odds favor this problem is caused by your work.

ForScan ODB2 scanner w ELM327 USB
 
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Cadehall234

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Oct 19, 2019
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yes I went over the checklist you sent. Yes I have an obd2 scanner and it’s only throwing o2 sensor codes for the exhaust. Ocassionally I will get a (MAF sensor out of test range) code and a p1000 code stays up. I took all of your advice from the previous post and spent the whole day checking everything you mentioned. I did a voltage drop test on the car and tested every plug and sensor front to back nothing was abnormal. The stock charge pipe is on it for now until tomorrow I get my new cold air intake for it. I see where you are coming from and it is very possible that my MAF sensor is bad but It’s not showing any signs that it is bad. On live data I can see the maf read a value when I blow into the charge pipe so it is working. What should the maf read?
my plug wires are in the right order. My injectors checked out and are working fine. I’m getting spark. No vacuumed lines open. All plugs are getting proper voltage. Crank position sensor as well. All grounds have been cleaned.

however while performing the voltage drop test I discovered there is a draw somewhere. The draw from the battery was about 27.30 mA. I spent the whole day unplugging sensors and checking them I got nothing. Also while the car is just sitting the alternator is warm.I received no draw from it though.
 

Onesick99GT

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Nov 20, 2018
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no start! You said it has spark. And injectors are good. My bet is bad fuel pump. A failed maf wont prevent the car from starting. If the maf fails there is a seperate table the pcm uses to make the car run. It wont run well but will start and run. People refer to this as limp mode or failed maf table. I bet you have no fuel pressure, which tells me bad fuel pump. If it cranks and turns over fine the charging system is at least working to some extent.
 

Onesick99GT

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Nov 20, 2018
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Dayton, Ohio
And if you havent went to a bigger maf or changed that out then changing your plenum and throttle body shouldn't make it not start. Been there done that.
 

wmburns

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Aug 14, 2009
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Yes I have an obd2 scanner and it’s only throwing o2 sensor codes for the exhaust. Ocassionally I will get a (MAF sensor out of test range) code and a p1000 code stays up.
So you don't think that a MAF specific DTC is an important clue? Especially since a MAF problem is a possibility, I would be following up on any MAF related DTC codes.

You did not state the results of the MAF disconnected test.

How about posting the full DTC codes? There are 1,000's and they each have a story to tell. Help us to help you by providing a full accounting of the symptoms.

Speaking of stories to tell, how about posting the MAF flow rate during cranking? Per the Ford service manual the typical idle MAF volts are 0.6-0.9 volts
 
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