'98 refuses to start

[baldguy]

So... I have read about 100 threads about similar issues today on this site and others. And while I'm definitely not a professional mechanic, I know my way around an engine bay and I've owned 3 of these SN95 cobras. That said... I'm stumped.

My car only gets driven on nice days, and we haven't had many of those around here lately. Today was looking like a great day to put the top down and let the pony run. The car just doesn't want to get out of the driveway. I've had issues lately with a rough idle when it has been sitting a while, so normally I just give it a blip of throttle when I start it and let it warm up a bit. I thought maybe the fuel pump was starting to get weak so I have been planning to replace it. I'm not convinced the pump is to blame today though. Here's what I know:

- I have never had this car refuse to start, just the rough idle and only after it has been sitting for a few days and that only lasts a minute or so. A couple of times it has started and then died, but always starts up right after.

- When I bought the car, the previous owner did not have the spare key with him so he mailed it to me (a couple months later). When I went to get in today I decided to try that key for the first time. Now it won't start with either key.

- There is fuel pressure at the test valve. it's not a ton of pressure, but fuel flows freely. The only gauge I have is the loaner I rented from Autozone, so I'm not sure how much I trust it, but it read about 10-12 PSI while I was cranking the starter.

- The coils are new-ish, and I've had no reason to believe they were struggling. The plugs and wires are new as of about 3 months and 1k miles ago.

- I have not checked for spark nor do I have a set of noids to check that the injectors are pulsing.

- While it cranks there will be a brief burble like it's trying to fire, but nothing resembling a real start.

- This car only has 54k miles and has been pampered. In fact, I just spent about $3500 on new wheels, tires, and front brakes because until today and as far as I could tell, it is mechanically in fantastic shape.

- The inertia switch in the trunk has not been tripped - the little red button is all the way down.

- perhaps most importantly, there are no codes to pull.

My current theory is that somehow that spare key messed with the PATS system, but I'm not 100% on that. The symptoms don't really seem to line up perfectly with a PATS problem. the key I've always used will not start the car now. The theft light will come on, then go off after about 4 seconds. A few times I've seen it flash slowly while trying to start. I've tried cycling the ignition on and off and back again, waiting different lengths of time between inserting the key and starting it, etc. I tried removing the negative lead from the battery for about 10 minutes then trying again. Nothing has worked. I even tried different positions on the steering wheel based on some other threads... that seemed silly but I'm getting desperate.

I don't think it's fuel- or air-related since I think it would start but run terribly if that were the case. It could be spark related but again, no other symptoms until today so I kinda doubt that. I guess it could be the ECU, but that seems normal too - I even tried re-flashing it using my SCT just to be sure I had a clean ROM... nothing.

please, oh wise men (and women?) of the forums - help!

 

[Quick98Cobra]

IMO either a pats issue or fuel pump went


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[ZeroDCX]

When testing fuel pressure, you're not required to crank the vehicle while doing so. Just prime the system.

IIRC, fuel pressure KOEO is supposed to be around ~42psi and hold steady at that pressure for a period of time. KOER is around ~32psi at idle. With the gauge reading 10-12psi, I'm not surprised the car gives trouble starting/wouldn't start.

Assuming PATS is functioning adequately, it sounds like you're having fuel pump/filter issues. Re-test fuel pressure to be certain.

However, I'm not certain you're not having PATS issues.

 

[baldguy]

no, nothing from the PATS system before today.

If it was the fuel pump or filter, and given that I do get fuel to flow out of the test valve, wouldn't you expect it to at least start but then just run like crap for a few seconds? I can't even get it to do that

 

[ZeroDCX]

If sufficient fuel pressure is not met, the vehicle should not start. But there are instances where the vehicle would run roughly versus not starting.

Example being, the system could pressurize enough to start the car but not enough to meet the demands of a running vehicle. Its easier to pressurize the system with no demands versus keeping adequate pressure with the engine running/consuming fuel. The system could also be rapidly losing pressure and fall below starting threshold conditions. You wouldn't know until further diagnosis is performed.

Retest fuel pressure KOEO/KOER (if possible) with a good known gauge to further diagnose your issue. If it is below specs, then you've isolated your issue. Also inspect all wiring, fuses, etc.

Can you hear the fuel pump prime the system when turning on the ignition?

 

[Snagmaster]

My 98 cobra had a fuel pump go out at 29,000 miles, right where the pumps have been known to fail.

It actually started after failing during a drive into town, drove home, next time out it failed again for good so they can seem to recover but still end up dead in the end, your pump may have lasted longer than most.

It's not too hard to change the pump but it really helps to have the tank empty beforehand, I had to remove the fill tube hose to siphon out the fuel but the job can be done by one person but you need to put the rear axle up on stands for more room.

You can do it as you said you know your way around a car, just be careful.

 

[Snagmaster]

Also you will need a set of the ford fuel line disconnect tools, pretty cheap, and remember that the 98 cobra uses a different pump than 97 and earlier

 

[NastyNate420]

once you release the fuel pressure it takes quite a bit of key cycles to prime the system back up to 40psi. try spraying fuel in the TB. might give you a better idea where to look.

 

[baldguy]

Just a quick update - I resigned to the fact that I needed a new fuel pump. Ordered a BBK 300 LPH and a new fuel filter, both of which should be here early next week. Then today I decided to try it again, and I'll be derned. It started right up! I don't know exactly what happened but I suspect it had something to do with the PATS. I'm happy that I don't have to tow it somewhere and I will likely go ahead and drop the new pump in at some point soon for some peace of mind. At least I was able to drive it today, and with the weather that is coming up for DFW this week I'll be very happy driving it quite a bit

 

[baldguy]

I'm bumping my old thread since it has all the same info I would need to re-type to give you guys some background. Anyway, A new fuel pump did not help my issue. Also the PATS system is not engaged. I have discovered a few new things that might help some folks smarter than me figure this out .

The biggest thing is that the plugs are wet with fuel after a day or so of sitting. I noticed this when I decided to change the plugs, and when I put the new plugs in it fired up faster than any car in the history of cars has ever started. Barely turned the key and it was running. I thought I had it fixed! I was wrong. a couple of days later it was back to the exact same symptoms.

so now, I know i can pull the plugs, let all that fuel evaporate, and it will fire right up. if I don't do that, it refuses to start. This really sucks for a car that only gets driven a few days per month. I have replaced the coils, the fuel pump, the fuel injectors (brand new 47lb FMR), the plugs, the wires, the battery, put a new tune in it (for the full offroad bassani exhaust), and it still acts the exact same way it did before all of that was done. When it runs, it runs fantastically. It will idle smoothly all day long, pulls hard to the redline, and never stumbles or complains once it's running. I'm convinced it has something to do with the fuel that is building up on the plugs (and in the heads) but for the life of me I can't figure out why that is happening. Even my trusted mechanic is a bit lost on this one. But it's perfectly repeatable - it won't start unless I go pull the plugs and wait about an hour then put them back in. then it fires up like nothing was ever wrong.

please help! I love my car, I just need to exorcise this demon and we can go back to being best friends. Thanks!

 

[Helomech74]

Why are you running 47lb injectors? Is the car boosted, do you have a tune specifically for those injectors? If not, I'm surprised the car runs at all.

 

[ZeroDCX]

Are you running forced induction? Why the 47LB injectors versus stock 24LB? I'm assuming you've received a tune for those injectors as well?

 

[baldguy]

yes, the injectors are sized for my application. It has a procharger, about 425 RWHP.

 

[ZeroDCX]

The fact that you stated your spark plugs were wet after a day of sitting, I would be looking into a fueling issue. Whether that be injector leaks or a tune issue.

When you tested fuel pressure, how long did you test for and did the system drop pressure?

 

[baldguy]

I tested with a rented gauge in my driveway for a few minutes (both KOEO and KOER), and it tested normal. Also when my last tune was done, he was monitoring fuel pressure the entire time. That's actually what made us swap in the 47 lb injectors, as it was starting to lean out at higher RPM. With the new injectors, that is no longer an issue. He said fuel pressure was perfect all the way from idle to redline.

edit: FWIW, the same exact symptoms existed with the old 24lb injectors and the new 47lb ones. I had been thinking leaky injector too, which is one of the reasons I was happy to buy new injectors. Unless I'm just super unlucky and got new ones that are also leaky, I don't think that was the issue.

 

[ZeroDCX]

The test should've been done for at least an hour. This would give the system time to demonstrate leaks if there were any. If you had a slow injector leak, you might not see pressure drop over a couple of minutes. You'd have better chances of seeing it over the period of an hour more than likely.

We're you running the stock tune with your stock injectors? When was the last time you inspected the FPR? A failed FPR would leak and the fuel would be consumed into the intake tract through the vacuum line leading to a rich condition.

 

[baldguy]

no, I had a tune specific to the equipment at the time. that being 24lb injectors, the blower, and mild exhaust. it had a lowered rev limiter to avoid the lean condition at high RPM. after I changed the exhaust out completely and removed the cats, I retuned. We opted to raise the rev limiter back up and coax out a bit more power, which meant going to bigger injectors.

during all that tuning and testing, fuel pressure never wavered. I don't have specific measurements to quote, but the tuner (whom I trust) was watching fuel pressure specifically to ensure the pump would handle the new injectors and all the fuel flow at high RPM/power. I don't know if there was something else we needed to look for, but he said it kept up with the flow easily.

do you think I should just swap the FPR to be 100% sure that's not it? I feel like almost everything else that *could* cause something like this has already been replaced. I'm going to do the plug wires soon for good measure, too

 

[ZeroDCX]

If this issue persists with all that you've done, I would be more inclined to say its a tuning problem.

I wanted to see if when you were running stock injectors you were on the stock tune and this issue was still present. If that was the case, then I would suggest a mechanical problem. But noting that you were tuned both times, I would note this issue to your tuner and have them double check the tune.

 

[baldguy]

it's worth a shot, and I had some of the same thoughts, but this go-round is the first time this particular tuner has worked on this car. he has done other ones for me but the tune that was in it when I bought it was done by someone else, years ago. I'll reach out to him and see if there is something he can think of to change in the tune.

 

[Shake&Bake]

Bad fuel injectors maybe? Sounds like they are leaking.

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