Bronco Engine problem- HELP!

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Sep 16, 2005 | 02:28 PM

#16

greystreak92

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From: Gateway to the West

Ford moved the TFI module over the the driver's inner fender in that monstrous heat sink to help alleviate heat-related failure of the module that was so common on the models that had it mounted to the dizzy. This change was made mid-year during production in 1991.

As for the ECT sensor, it is mounted in the lower intake manifold just behind the thermostat waterneck. If you want to swap in a fix-value resistor to troubleshoot, put a 5500 ohm resistor in its place. At this resistance value the computer will assume "cold start" conditions. Perfomance modfiers love this trick to force the computer to dump more fuel all the time. (Great trick for the track but not very efficient otherwise). The resistance values for the ECT sensor are as follows:

Temp. (Farenheit) / Voltage / Resistance (ohms)

248 / 0.27 / 1,180
230 / 0.35 / 1,550
212 / 0.46 / 2,070
194 / 0.06 / 2,800
176 / 0.78 / 3,840
158 / 1.02 / 5,370
140 / 1.33 / 7,700
122 / 1.70 / 10,970
104 / 2.13 / 16,150
86 / 2.06 / 24,270
68 / 3.07 / 37,300
50 / 3.51 / 58,750

Sep 18, 2005 | 09:59 AM

#17

illuzion

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Ok about 80 degrees outside, after sitting overnight here is ECT data:
2.93V
23degC
only problem is engine started right up no problem. So it really tells us nothing. I left the scanner connected to the truck, and will get ect data every time before i start the truck until I catch it when the problem is there, then we can rule out the sensor one way or the other for sure.

Also how does a 5500 ohm resistor simulate cold start conditions, unless of course you meant 55000 ohms

.

Brian

Sep 20, 2005 | 08:57 AM

#18

illuzion

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Ok, I have been patiently waiting for this intermittent problem to come up again, so I can catch it with a scanner connected. When the engine was not run for two hours it was warm, not totally cooled to ambient, Started cranking with no fire, so I looked at scanner, ECT value was 1.78V read by the ecm, and it showed 48degC. Ambient temp was about 84. Are these values low enough to rule out the ECT sensor as the cause of the problem??? Can exhaust backpressure cause an intermittent condition?? Here are some recent tips, first my wife commented it smells like rotten fish when shut off. Also while driving, the air conditioning ducts seem to be snapping back and forth between defrost mode (so a/c is coming out the defrost vents) and standard mode, dont know if this is related, but could be linked to intermittent loss of vacuum. I put a vacuum gauge on the intake manifold, it developed about 16psi of vacuum immediately after startup, when accellerated, the vacuum level dropped, then recovered, when engine returned to idle, vacuum recovered quickly.
Thanks
Brian

Sep 20, 2005 | 06:33 PM

#19

greystreak92

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From: Gateway to the West

Quote:

Originally Posted by illuzion

could be linked to intermittent loss of vacuum

You are on the right track with it. A clogged CAT will effectively slow airflow through the entire engine creating a drop in vacuum as well. It may have cracked part of the substrate INSIDE. I had an old Pontiac do this and when the substrate cracked, the piece that was loose inside the cat was acting like a butterfly valve and snapping shut against the back of the cat when ever I accelerated effectively bogging it down until one day enough of the bits and pieces of the substrate jammed into the exit side of the cat to completely stall the engine.

Quote:

Originally Posted by illuzion

Also how does a 5500 ohm resistor simulate cold start conditions, unless of course you meant 55000 ohms.

No, actually its 5500. Its based on a racing trick that "fools" the ECM into thinking the engine is not FULLY warmed. If you were to make the ECM think the engine was dead cold (50 deg. F) or lower, once the engine warmed up the fuel/air mixture would be so rich it would flood the engine or ruin spark plugs and burn valves. For testing purposes like you are attempting though you could use a higher resistance for short periods of time.

Last edited by greystreak92; Sep 20, 2005 at 06:39 PM.

Sep 22, 2005 | 09:09 AM

#20

illuzion

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Okie, here is the latest on this one, in order to help narrow this down, I waited until the problem happened, then immediately pulled off the mass air duct and sprayed a lot of carb cleaner in the duct and tried to start it, no combustion, I guess this kinda narrows it down a bit, I also took it for the local 17 point free exhaust system inspection, aside from loose/missing heat shields, they said the cat/exhaust system was fine, no signs of overheating/blockage. At this point I would assume this is an ignition problem until proven otherwise, right? My first step is to replace the Plat+4 Plugs with regular autolite, my local performance shop said to stay very far away from platinum and even iridium plugs, and highly recommended a autolite 764 with a .038 gap, can any verify this?
Thanks
Brian

Sep 22, 2005 | 09:53 PM

#21

Tazz452

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I mention earlier that I too had serious problems with patinum plugs that went away after changing to autolites.

Sep 22, 2005 | 10:00 PM

#22

illuzion

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Ok latest update, I am very close to giving up and bringing this to a dealer, not that I know what they will do that I have not, I did replaced the plugs with plain old autolite copper 764 .038 gap.

Here is what I have tried. Spark verified during cranking when problem was occuring by holding a ground lead near distributor output. I also went as far as temporarily connecting as MSD 6A box just to make sure spark was hot enough (all this did was make the engine miss/knock). Also ECT sensor seems to be reading good, so I will stop looking at it. I also tried spraying carburator cleaner directly into the throttle body while cranking, no ignition, won't this rule out a fuel problem??? I did a compression test, 90psi in each cylinder (except #7, 98psi). No Codes (111), KOEO or KOER.
Can anyone else help, or do I just throw in the towel?
Thanks
Brian

Last edited by illuzion; Sep 22, 2005 at 10:05 PM.

Sep 23, 2005 | 12:15 AM

#23

Tazz452

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Is it possible that your timing is off? I'm not sure if it would send a code or not, but if it is too far off it won't start at all. Also have you checked to make sure it isn't just loose. This wouldn't explain that cold start only prob but I hate to see you go to the dealer. Also, does it really matter that it has to crank a little longer to start or are you trying to make sure that you don't have the beginnings of a larger problem.

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Sep 23, 2005 | 07:59 AM

#24

illuzion

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I really don't want to "live" with this problem, sometimes it can get very bad and it is only going to get worse. I also plan on doing some performance upgrades in near future, so I would like to make sure engine is in excellent running condition first (another reason I did compression tests). As far as timing goes, if it was off, the engine would idle rough. This engine idles rather smooth, also timing does not "move itself", since I never messed with it, and distributor is very tight, (I tried rocking it by hand, it will not move), so I can't see that being the problem, the only possibility I can see is that the system is not electronically retarding the timing enough during startup (I don't know how to test this), but if ign timing was off, I would expect to see more probs than just during startup, and especially not an intermittent one.
Thanks
Brian

Sep 23, 2005 | 11:27 AM

#25

illuzion

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I just spoke to a tech from a dealer today (owner of dealer is personal friend of mine). Here was his take on it, the more of the story I told him, he seemed to feel that it was not ignition related, not exhaust related. He seemed hell bent on a fuel problem. He said there are really two possibilities. First off he was very suspicious of my "aftermarket" fuel pump, he told me he has seen trouble with them before, especially intermittent hard starting, my question was if the system freshly primes to 40psi before starting, what difference does it make during startup? His second concern sounded much more plausible, and is one I honestly never considered. He is suspecting an intermittent pintle seat on a fauly injector, that is "dripping fuel into the cylinder when engine is off". This would create a highly rich (possibly flooded) condition upon startup. What I plan on doing tonight is priming to 40psi, and leaving a fuel pressure gauge connected overnight, and check the pressure in the morning, I need to see if there is a significant drop in rail pressure before starting (and repriming the system, and getting rid of my only hint of the problem) when the problem is occuring.
Brian

Sep 23, 2005 | 02:51 PM

#26

illuzion

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Okie did a little testing since my last post. Here is the story, I put a pressure gauge on the rail, primed the system to 40psi, and came back in two hours, gauge read 20psi, reprimed to 40psi again, came back 2 hrs later, gauge read 16psi. Now this seems to be abnormal, it should hold pressure for more time than that right???? Tried starting it, and it *was* hard to start, when it finally turned over, I saw some smoke coming from tailpipe (not a lot, but some). So I see 3 possibilies possibility #1 is the check valves in my "new" fuel pump are leaking, and fuel is running back into the tank, possibility #2 is Fuel is leaking from an injector into the cylinders, possibility #3 is a leaking check valve in the fuel pressure regulator (if it even has one). Any idea how to narrow this down? Or does anyone disagree with me or my diagnostics???
Brian

Sep 24, 2005 | 02:53 AM

#27

greystreak92

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From: Gateway to the West

Sounds plausible. The FPR only controls inbound pressure AFAIK so there is no check valve there. A certain amount of fuel pressure should be maintained for DAYS. The leak-down rate should be a couple of psi each DAY not each hour. If you turn the key "ON" but don't "START" the truck, can you hear the fuel pump prime?

Sep 24, 2005 | 07:32 AM

#28

illuzion

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Ok, thats what I was interested in knowing, what the leak down rate "should be", The FPR could be "leaking through" and passing fuel, as I said in previous post, I can "prime" the system to 40psi no prob, key on engine off the pump runs for 5 seconds, to prime then shuts off. This problem seems to be getting worse. I just keep wondering if fuel was returning to the tank (and not leaking into a cylinder), would it still be hard to start?? Because the system should reprime before starting anyways. I have even tried cycling the key a few times before starting to make sure the system is fully primed. I am just praying the fuel pump is ok, I really, really, really, really do not want to have to drop that tank again.
Brian