[TTBlows]

I'm at the end of my rope on this one and could really use some input. Vehicle is an '87 Bronco/302EFI/C6.

Problem is I can only get about one start every 12 hours. When it does start, it runs fine and has never died on its own. So far it appears it would run for days and days as long as you never shut it down. You don't even have to get up to operating temp - start it, let it idle for 30 seconds, shut it off and forget it; you might get it to restart 6 hours later.

CODES: only codes I'm getting are for insufficient EGR flow and open VSS circuit. Regarding the EGR, I don't care and I know why - the tube which feeds the EGR is packed solid w black soot. Regarding the VSS, I've never before encountered this, but I swapped in a different VSS just in the interest of due diligence. I then cleared the codes but have not since checked to see if the VSS code remains.

FUEL: I hear at least the hp pump prime when I turn the key. I'm a little unclear on the dual pump abortion pre-'90 but the fact that it primes, starts once a day, never stumbles while running and never dies on its own makes me think pumps are not the issue. FP while cranking is 39psi but I've not been able to check FP when running.

It does smell very rich when cranking which leads me to:

IGNITION: using both the shock-yourself-with-a-screwdriver technique and a HF in-line ignition tester, I do see (and feel) spark while cranking during no-start episodes.

Today I pulled the plugs and they were all oil-colored altho not really oil-soaked. They smelled very strongly of fuel. Given the low cost I simply replaced all the plugs today, but no change in symptoms. While the plugs were out I ran a dry compression test and got 125 to 140 in all cylinders (better than I would have expected).

I've also swapped the cap and rotor as the existing ones were in poor condition.

Early on I replaced the TFI module as you'd be remiss to do not so anytime such a problem appears on these vehicles IMO. No change.

Given the fuel smell and appearance of the old plugs I'm still suspecting something w ignition, but all that seems to be left is coil, which is easy enough..........but I'm not confident it's the issue. Would a bad or weak coil only allow one start per day but never cause the vehicle to die while running???

OTHER THINGS I'VE DONE:
-replaced the TPS as I had a bad TPS cause almost identical symptoms on a '95 351, altho in that case I was getting a TPS code and here I am not. No change from new TPS.
-swapped the IAC in an act of desperation - no change
-swapped in a different MAP sensor - no change
-visually looked for obvious vacuum leaks, and am surprised that all the vac lines appear to be in very good condition. Have not checked w starter fluid, however.

I'm open to other theories. Maybe something w injectors leaking down when I shut it off? Alien conspiracies? Still a sensor issue? What else is the EEC looking at for start parameters?

 

[nelbur]

I know from experience that a bad coolant temp. sensor can keep an engine from starting when warm, and allow it to start after it cools down. If this sounds like what you are seeing you might want to replace yours. It is on a riser where one of the heater hoses connects, on top of the engine below the throttle body. However, I would expect it to be mentioned in your code check. I assume you have no spark when it will not start. If you have spark it is not the coolant temp. sensor.

 

[Daves 88']

In the Haynes troubleshooting section, it defines a faulty smog system as a cause for a no start issue. Clean the pipe out with a wire hanger. I had to clean out an EGR tube with a wire hanger before. It's easy, takes time, and is cheaper, smarter, and more environmentally friendly than buying a new one. It doesn't waste valuable parts available for those who really need it, because they actually have a broken pipe.

 

[Daves 88']

Hopefully you have not hurt your other smog equipment apparatuses by running your motor with a clogged EGR tube. Like maybe burst the vaccum diaphram inside your EGR valve. No offense, but the old saying "K.I.S.S" it applies here. Keep. it. simple. stooge (K.I.S.S).

 

[TTBlows]

I know from experience that a bad coolant temp. sensor can keep an engine from starting when warm, and allow it to start after it cools down. If this sounds like what you are seeing you might want to replace yours. It is on a riser where one of the heater hoses connects, on top of the engine below the throttle body. However, I would expect it to be mentioned in your code check. I assume you have no spark when it will not start. If you have spark it is not the coolant temp. sensor.

I considered ECT too but yeah, no codes. I DO have spark during no-start episodes. (But why would it matter - ECT shouldn't preclude spark, only tell the EEC how to handle mixture?)

As for the EGR, I don't see how a clogged tube could cause a no-start condition. It's not supposed to open the EGR valve at idle anyhow, and even if it did open the EGR valve there's no way exhaust gases could get into the intake. I can try to clean it just the same - this damn '87 stuff runs under the upper IM and goes somewhere. On my '90 it goes into the front of the right exhaust manifold which is far more straightforward and accessible.

 

[Daves 88']

I considered ECT too but yeah, no codes. I DO have spark during no-start episodes. (But why would it matter - ECT shouldn't preclude spark, only tell the EEC how to handle mixture?)

As for the EGR, I don't see how a clogged tube could cause a no-start condition. It's not supposed to open the EGR valve at idle anyhow, and even if it did open the EGR valve there's no way exhaust gases could get into the intake. I can try to clean it just the same - this damn '87 stuff runs under the upper IM and goes somewhere. On my '90 it goes into the front of the right exhaust manifold which is far more straightforward and accessible.

It is just the way it works. I had a Toyota do the same thing to me. I know it is a bish to get to. You may have to take off the upper IM to get to it too, unless you want to try to get it all from the EGR side, while simultaneously using a vaccum cleaner modified to suck out the soot while operating on the Bronco . That is risky though. :doh0715:, you gotta do what you gotta do.

 

[Caddylackn]

KISS,

Spark or fuel or timing

I have heard of similar type of no start problems on other cars. They traced it eventually to the factory coil, something about when it got hot it leaked voltage to the ground internally. Wouldn't restart until cold. It doesn't take a lot of spark to keep a motor running. Once shut off it would still have voltage, just not the 40,000 volts needed and made it hard to start and diagnose. These cars were not fuel injected, but it wouldn't hurt to rule out the coil or the induction circuit that triggers the coil. You have some fuel during the no start, since your plugs are wet. If you pull a plug and ground it to the block it should be bright blue or white. It it is yellowish than it is not hot enough.

If in doubt your spark is good, pull the plug off another car that runs good and ground that and compare. A good spark is pretty obvious compared to a weak spark.

To rule out any fuel issues, see if it will start off starting fluid. Not a lot, just a 5 second burst. It should catch immediately if it was a fuel starvation issue.

It could be a coolant temp sensor, but it should still start, just be harder to start without enrichment. Like 20 seconds of cranking. A car with a bad temp sensor should start easy on starting fluid.

I think we can rule out timing since it runs good when running. It would run like crap when warm if it was timing.

 

[bluesuper74]

I'm grasping at straws but you have spark and fuel, whats left is air. How is your filter? It would have to be real real dirty to stop a truck from running at all. How is the intake piping,clear? Also if air can't get out fresh air cant get in. Is it possible the exhaust is clogged?

 

[nelbur]

The ECT can kill the spark if it gives a faulty reading that tells the computer that the engine is overheating big time.

 

[Daves 88']

The ECT can kill the spark if it gives a faulty reading that tells the computer that the engine is overheating big time.

IGNITION: using both the shock-yourself-with-a-screwdriver technique and a HF in-line ignition tester, I do see (and feel) spark while cranking during no-start episodes.

 

[Daves 88']

KISS,

Spark or fuel or timing

I have heard of similar type of no start problems on other cars. They traced it eventually to the factory coil, something about when it got hot it leaked voltage to the ground internally. Wouldn't restart until cold. It doesn't take a lot of spark to keep a motor running. Once shut off it would still have voltage, just not the 40,000 volts needed and made it hard to start and diagnose. These cars were not fuel injected, but it wouldn't hurt to rule out the coil or the induction circuit that triggers the coil. You have some fuel during the no start, since your plugs are wet. If you pull a plug and ground it to the block it should be bright blue or white. It it is yellowish than it is not hot enough.

If in doubt your spark is good, pull the plug off another car that runs good and ground that and compare. A good spark is pretty obvious compared to a weak spark.

To rule out any fuel issues, see if it will start off starting fluid. Not a lot, just a 5 second burst. It should catch immediately if it was a fuel starvation issue.

It could be a coolant temp sensor, but it should still start, just be harder to start without enrichment. Like 20 seconds of cranking. A car with a bad temp sensor should start easy on starting fluid.

I think we can rule out timing since it runs good when running. It would run like crap when warm if it was timing.

IGNITION: using both the shock-yourself-with-a-screwdriver technique and a HF in-line ignition tester, I do see (and feel) spark while cranking during no-start episodes.

 

[Mr Bell]

Kinda sounds to me like it is flooding out when you shut it off, if you have the throttle fully depressed and then turn the key to the on and start position. This is a clear flood mode and will shut off the injectors. Also is your fuel pressure regulator burst?

 

[BIGED1987]

What about timing being too far advanced? My truck ran like a champ, but wouldn't start after getting warmed up. Mine wouldn't turn-over very quickly, but if I turned the distributor back just a bit, then tried it, it would fire right up. It's worth a shot if you are experiencing a slow turn-over rate when hot.

 

[Daves 88']

:doh0715:

 

[Daves 88']

What about timing being too far advanced? My truck ran like a champ, but wouldn't start after getting warmed up. Mine wouldn't turn-over very quickly, but if I turned the distributor back just a bit, then tried it, it would fire right up. It's worth a shot if you are experiencing a slow turn-over rate when hot.

So why wouldn't you think a colgged EGR tube was not the culprit? I had a code 44 (inoperative thermactor system) for a long time, and the Bronco did not want to start after being hot. Mine was vaccum hoses, and other small stuff, but his is a clogged tube. Why not the clogged tube?

 

[Cheesehead]

The ECT can kill the spark if it gives a faulty reading that tells the computer that the engine is overheating big time.

Or telling the computer it is too cold and flooding the cylinders.

Kinda sounds to me like it is flooding out when you shut it off, if you have the throttle fully depressed and then turn the key to the on and start position. This is a clear flood mode and will shut off the injectors. Also is your fuel pressure regulator burst?

Check the ECT. I had this exact issue with my '88 when I first brought it home. I went through everything I could think of then finally gave in and took it to a shop. They replaced the ECT and bamm! She started up. The mechanic stated when the ECT goes bad it can tell the computer the engine is very cold and flood the cylinders with gas. So much that it won't fire. You letting it sit for 12 hours or more probably gives it time to let some fuel evaporate and then the plugs will fire. G/L