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Discussion Starter · #1 · (Edited)
EDIT: I guess it would help to mention it's a 2000 GT.

So, I finally got the car back together and running. Cranked it up, and it cranked first try. I let it idle for a bit, but it was almost 2:00am so I didn't take it for a drive. The next day, I cranked it and once it warmed up, I tried to take it for a drive, but it died on me. After it died, it cranked right back up, but immediately died again. for a while, it would just turn over but not start. Then it started again, and just keeps stalling out immediately. I thought maybe the gas that was in it was no good, and it hardly had any (sitting on E), so I put some fuel treatment in it and a full 5 gallon can of gas. I messed with it again for a few hours, cranked it and held the gas down to try to burn out some of the gas, and as soon as I let off the gas it dies. I eventually got frustrated, and quit messing with it. The next day, I cranked it and it idled fine again. I backed it out of the garage after it warmed up and when I pushed in the clutch again, it died. I got it cranked and drove it, but never stopped while I was driving and it never died. When I pulled into the driveway and stopped, it died again. This happened again the next day. I can crank it and keep my foot on the gas and it wont die. I can keep it at idle RPM by with my foot barely on the gas, and keep it running no problem. As soon as I let off, it dies. Only after it's warmed up though. When it's cold, it will crank and idle fine until it warms up. Once it warms up, if I rev it or put any load on it, it stalls once the clutch is pressed again.

There is no check engine light, but I scanned it for codes and came back with P0172, Rich bank 1. I tried cleaning the MAF, IAT, replaced the IAC valve, checked all vacuum lines, checked all connections in the air intake. I've pulled the negative battery cable and let it sit for 10-15 minutes, nothing has helped. I cleared the code and it hasn't come back, but it is still doing the same thing. I tried running it with the MAF unplugged, and no change. The only thing I haven't messed with is the throttle position sensor and the EVAP canister (one of the checks for a P0172 code). I know nothing about the EVAP system, so I wouldn't know where to start with that. I do not have a fuel pressure gauge, but I did depress the schrader valve after it died and it sprayed fuel, so it's got and is maintaining pressure, I just don't know how much.

I just had the heads rebuilt with new valves, springs, retainers, seals and had them all cleaned up. Installed CMS stage 1 cams, BBK 73mm throttle body, it has a C&L CAI, BBK tuned length shorty headers, BBK catted x pipe, Magnaflow catback. The last thing I tried was swapping back to the stock throttle body, but it didn't help anything. I'm at my wits end. If anyone has any advise, I'm all ears. My next step is to take it somewhere and pay someone else to fix it, but I'd rather just do it myself if someone can point me in the right direction to try to diagnose it and fix it.
 

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Could still be fuel pressure related, by pressing the shrader valve and having fuel come out shows there is some pressure in the lines but it may not be enough to run. Have you checked the throttle body? Could be vac lock. Can you datalog?
 

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Discussion Starter · #3 ·
Unfortunately, I do not have any way to data log. I have an OBD MX dongle that I use in my Ram, and wanted to download Forscan, but the only laptop I have is my work laptop and they're not big fans of us downloading and running random applications. I have an old ipad and a newer iphone, but from what I've read, forscan on ios isn't great and is limited in it's capabilities.

I have checked the throttle body. I initially installed a BBK 73mm, and when I couldn't keep it running, I reinstalled the stock one. Same issue with both occurring in the same manner, which leads me to believe it's not a throttle body issue. I am planning to go pick up a fuel pressure gauge but haven't had a chance yet. I can drive it as long as I do not let it get back to idle. I drove it for 15 minutes on two different occasions, got on it a bit, it ran fine. I was on some back roads, so I just kind of rolled through the stop signs and never let it get back to idle speed, so it didn't die. When I pulled into my driveway, I had to just about stop (car is lowered and driveway is inclined) and that is when it died again. I could be wrong, but I would think if it was a fuel pressure issue, it would be an issue through the RPM range, and worse on hard acceleration? I still plan to check to rule it out, I just have doubts that is the issue.
 

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You’re probably right but it’s best to go back to the basics. I don’t know who told you that about Forscan on iPhone but that’s not true. The iOS app can’t make changes to pids but can datalog pretty much anything. I use is all the time on my iPhone.
 

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Discussion Starter · #5 ·
Interesting, I just downloaded it. I'll give it a go since I already have the OBD dongle.

I did discover something interesting today, though I'm no less confused. I was messing with everything, and pulled off the vacuum line that connects at the back side of the throttle body and goes to the EVAP canister (or purge valve, not sure, it's the large diameter hose in the pic in my hand). I forgot to hook it back up, and the car started and idled without stalling. It did idle pretty rough, but it did not die. I heard it hissing and realized it was off, and as soon as I put it over the end of the nipple, it died. I cranked it back up and immediately died. I pulled it back off and cranked it, and it ran (rough) again. I was thinking there was a problem with the EVAP causing it to die on me, then I capped that nipple with a rubber cap, and it still died on me again. Since it still died when I capped that nipple, I'm not sure if it is a problem with the EVAP system or not. It's almost like its choking itself off somehow, but I cant imagine how that's happening. It would make sense for the rich code if it's not getting enough air, but I don't know how it wouldn't be.

I did find a small vacuum hose behind the glove box not connected. Where the vacuum hose comes in through the firewall, it runs to a tee. One side of the tee goes on to the little vacuum manifold, and the other branch goes into a black canister mounted directly behind the glove box. That branch was out and open. I reconnected it, but it made no difference.
 

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I know you swapped out the iac already but it would seem there is no air bypassing the throttle plate, or not enough. That’s why I asked about the throttle body. If you can datalog, check the iac duty cycle. If it’s maxed out at idle or close to it I’d say it’s either doa or there is a restriction. Check the iac vacuum hose for obstructions. Also, I know in the video in your other thread you have the right iac with the black vent. It’s probably not the issue but make sure the new one has the same vent. The later new edges use a different iac which is not interchangeable.
 

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Discussion Starter · #7 ·
It does have the vent.

I do have a question about the IAC. I was reading somewhere that if you take the IAC out, and apply 12v to the pins, the plunger should move. For both the old one and the new one, I can hear what sounds like a little motor actuating, but the plunger does not physically move. I reversed the + & - and same, no movement of the plunger, but can hear it actuating. The "old" IAC looked new as well, so I was hesitant to even buy one, but did anyway. If it should move, I will take it back and get another one. They both move freely and easily if I move them myself. I'll pull the vacuum hose and check it as well.

EDIT: Just went and checked. Absolutely no obstruction in the hose.
 

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Discussion Starter · #8 ·
Apparently, OBDlink MX bluetooth does not work with iOS. According to OBDlink's website, the MX+ does, but that is $140. I'm going to download that app on my computer and just delete it when I get this taken care of.
 

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Discussion Starter · #10 · (Edited)
So, I cranked it, and let it jump around. It didnt die, but the RPM was dropping down to 200-300 then jumping back up, then down, and up several times. I thought it was going to die, but didnt. You can see in the log when most of the lines level out, it started idling like normal. The interesting thing to me is manifold vacuum is showing nothing then it jumps up and that was not long before it leveled off. Let me know what PIDs you are interested in, and I can clean up the graph and do it again.
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It sounds to me like you have an intermittent issue with the fuel rail pressure sensor. It monitors vacuum and makes changes to fuel based on vacuum. i believe that is where the vacuum signal comes from. Thats where i would start.
 

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After looking closer at the data log, the vacuum starting to read seems to conicide with the car going into closed loop so it may ignore the sensor until closed loop but with that said, even after it goes into closed loop, the vacuum is all over the place. You said the car smoothed out when all the lines started going flat but vacuum is still all over the place. It still looks like the sensor is reporting huge variances in vacuum which shouldnt be happening if its idling stable.
 

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Discussion Starter · #13 ·
What sensor reports vacuum?

Nevermind - I see above where you mention the fuel rail pressure sensor. I’ll see if there’s any way to test that sensor
 

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I always wondered where the manifold vac pid got it’s signal from. I thought it was inferred. Anyway, I’ve datalogged that pid before and it was all over the place so I don’t use it. Still something to rule out though. If anything it’s going to be on the vac side of things and not electrical. From what I’ve read the electrical side of the frps either works or doesn’t. Also I know the maf signal is all over the place and so are the rpm’s but theres one part of the log where the maf signal spikes then drops almost to 0. And when that happens your fuel pressure drops too.
 

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What sensor reports vacuum?

Nevermind - I see above where you mention the fuel rail pressure sensor. I’ll see if there’s any way to test that sensor
You should be able to use a vacuum pump to introduce vacuum and validate what the ecu sees and if it fluctuates when a steady amount of vacuum is introduced. I'm not 100% it comes from the sensor but it's the only sensor on the engine that is connected to a vacuum that monitors manifold vacuum/pressure that in aware of so i would assume that's where it gets it's reference.
 

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Discussion Starter · #18 ·
So, I just logged a couple more times just to check it out. These were consecutive within a few seconds of each other. First is a screenshot of what I'm monitoring.
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Then the 3 logs. I'm attaching them as thumbnails so you can open them up to see. It's really strange to me. The first one, I cranked it, it immediately died, then I cranked it again. I let it run a while then shut the log off, but left the car running. The second image is the later part of the first one (it was long). You can see the throttle blip for reference.
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Then I restarted the log and let it run for a while. This is where it got weird. Everything is all over the map. All I did was stop the first log, and start it again.

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Then I killed it, restarted the log a 3rd time, and restarted the car. It immediately died, I restarted it again, and it logged like it wanted to die then leveled off and idled again. After a while, I rev'd it, it died, I cranked it again and it died again. That's when I stopped the logging.
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This car has some issues, and I have no idea where to start. I plan to get to Dwain's suggestion, but it is probably going to be sometime next week before I can mess with it again.
 
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