My T-Bird stalls when put in gear and has a low/rough idle

[1986TBIRDV8]

Hey all, first time on this board...

Anyway, My '86 Thunderbird has been acting up recently. It has a 302 (5.0L) V8 in it and she starts with near perfection but then it goes to crap from there. When she idles normally, it's around 400 rpms steady. Then it'll jump up to and sometimes over 1,000 and then back down to even 200 rpms. Sometimes it'll kill too. The real problem is when I put it into gear. It's rpms will drop so low, I can't tell if it's running or not. Then, a lot of the times it will just take a crap on me and kill once again. The dashboard is all digital and when it kills, the oil bar (says how much oil I got in the car) will say that I have no oil when in reality it's fine. The other day, I put straight through exhaust on straight out of the manifolds. Maybe I got rid of to much backpressure and brought the idle down too low??? Thanks in advance.

[curtis73]

If the problem occurred at the exact same time as the new exhaust, then maybe you've altered the backpressure to the point where further tuning of the fuel curve is required. If it didn't occur the same time as the exhaust, its not the problem.

Secondly, the oil bar doesn't show you how much oil you have, it shows you oil pressure. Its normal that it should drop to zero when the engine stalls.

When someone says hunting idle I usually say that its something to do with ignition. If the idle goes up, down, up, down steadily, then its almost always a spark issue. If yours is just jumping up every once in a while and stalling, I would check for vacuum leaks.

Proper idle for that car should be more like 600 in neutral and 500 in gear.

[1986TBIRDV8]

Thanks for the response.

OK, I'm going ot believe you on the oil bar. At the top it says H then in the middle it says NORM than L at the bottom. Now if what you say is true, when I'm drving sometimes, it'll beep and show no oil pressure, but then the bar will go back to NORM. I DO have a leak somewhere though, out of the valve covers or back of the EFI. About a quart a month. Would this have anything to do my idle and stalling?

[curtis73]

It shouldn't make a difference in your stalling. I am concerned about the beep and low oil pressure thing.

Let me clarify (and maybe confuse) the oil pressure gauge. It is definitely an oil pressure gauge, but it doesn't indicate pressure like a gauge with numbers does. In order to save some money, many manufacturers use a gauge to look good, but all it does is show one of three settings; too low, just right, or too high. The fact that it indicates "L" while you're driving means that its falling below 10 psi which is way too low.

As long as you make sure the oil level doesn't fall below the level of the bottom of the dipstick, no engine damage should occur, but that low oil pressure thing scares me.

How many miles are on it ?

[1986TBIRDV8]

It has 165,5XX miles on it. I checked with a couple local mechanics and they said it was probably a faulty sensor or computer. (without them looking at it) It always is at 4 bars, which is smack dab in the middle of NORM on the gauge. Then sometimes, it'll beep and go straight to just one bar, and the oil can will blink. It'll do that for any where from 2 seconds to about a minute or more, then it will go back to the normal 4 bars. Then it will reapeat that and do it randomly and eventually just stop and go back to the 4 bars and stay that way. Thanks.

[curtis73]

Yup, you have one of the three position gauges. That loss of oil pressure is a very serious condition that shouldn't be taken lightly. Without oil pressure, the engine can very quickly seize. If it seizes, it becomes a boat anchor. It most likely won't be rebuildable without intense and expensive machine work.

I guess what I'm saying is, even if you fixed the rough idle problem, you have an incredibly tired engine that has outlived its expected life by a long shot. I might consider not spending too much money diagnosing sensors.

[1986TBIRDV8]

Whoa, I think you have jumped to a conclusion WAY to early. When I had a mechanic put new brake drums on it, I told him to take a look at other parts of the car. He said the engine was in excellent condition and was worth $500 alone. So I HIGHLY doubt what you say about it. Can you give me any info that can support your statement? What makes you so sure that it's not a faulty sensor or bad wiring? I've heard people getting over 250,000 miles on that 302.

[curtis73]

Don't go nuts You gave me the evidence. Random loss of oil pressure is a HUGE thing. Looking at the outside of the engine tells you nothing about its value, especially if you're losing oil pressure; an internal problem that your mechanic couldn't have diagnosed by looking at it. A possible vacuum leak (which is what the idle problem sounds like to me) means a partial engine teardown. You said it yourself; the engine is worth $500 alone if its in great shape, but the labor and parts to fix your problem might be $1000. I also think your mechanic was a little optimistic. I just bought a 351 with 46,000 miles on it for $200 with accessories.

I'm not being confrontational or sassy, I just know that it won't do any good if I candy coat everything. I've had many years experience with this kind of thing and I stand by my opinion.

There is a good chance that its just a sensor, and it might be $20 to fix the idle problem, but the oil pressure problem is the big one. If it were my car, I wouldn't turn the key until I fixed the problem or you might end up with a seized engine.

[1986TBIRDV8]

I found out what the problems were. The oil perssure gauge was just a bad connection. Fixed that very easily. And for the idle and stalling, it was just a half clogged air control valve. Total cost: $0.

"the oil pressure problem is the big one" Yup, sure...

Good Day Sir!

[curtis73]

Good. I'm glad it all worked out.

[asemstr]

One thing most Ford techs quickly learn is the stock oil pressure, and coolant temp gauges are woefully inaccurate . They're just for ornamental use only! The oil pressure sender is real bad about shorts, lapses, and all-out "Coronaries" so you need to rely on hands on testing to isolate actual engine concerns

[1986TBIRDV8]

Thanks, I'm glad too

But, say the gauge was actually doing its job and I WAS losing oil pressure randomly, what would the symptoms be before my engine siezes up like a boat anchor.

Thanks.

[asemstr]

Rapid changes in actual oil pressure usually doesn't occur with proper oil level, unless you are one of the few that lets the oil get low enough to sloshe away from the pick-up which is one posability. Other than that I can't think of any others that would apply to your 5.0! I really wouldn't worry about the oil pressure because you'll hear alot of valvetrain noise if it gets to low!

[curtis73]

although I don't have tons of experience with 302s, I had a pontiac 389 go south on me. In a matter of a mile and a half, here was the progression of things:

The oil pump input shaft snapped dropping pressure to zero. I didn't have a working oil pressure light at the time. Within the next several hundred feet, the lifters bled down giving nasty valve chatter. About the time I heard the lifters clattering it spun a main and a rod bearing. Before I could get my foot off the pedal and the turn signal on, locked up tight. Then there was some mild boiling over from the very fast heat created. 2 cylinder walls were scuffed pretty badly, one rod was a waste, three journals were scored to the point where an extreme undercut could have been done, but not advisable. I couldn't even use it as a core.

My solution was a Caddy 500 in its place, so it was a fine move, but it can be a very fast process from fine and dandy to complete death.

asemastr is right. complete loss of oil pressure is rare unless the pickup tube falls out, the pump driveshaft snaps, or there is a sufficient enough air leak in the pickup that the pump cavitates. I've also seen the teeth of the pump just snap off.

What concerned me so much about yours was the all-or-nothing gauge. It wasn't necessarily telling you that you were dropping to zero, it was telling you that it was dropping below 12 psi (or it might be 8... again, not a ford guru). That means that at 5000 rpms, all we know is that its making at least 13 psi when it really needs more like 40.

Turns out it was a faulty wire (thank goodness). Didn't mean to make you panic, but those all or nothing gauges tend to make more of a problem than they're worth in my opinion.