Okie, this is a very strange one, I have baffled almost everyone with this, I'll start with the problem, then go into some history/troubleshooting I have done so far.

Vehicle 94 Bronco XLT 5.0 302 EFI, E4OD
Current Problem started 2 days ago: Excessive cranking (5-7 seconds) before engine starts ONLY WHEN COLD (hasn't run in at least 1-2 hrs), hot restarts fine. Idles very smooth

Possible related problem started several weeks ago: Not making full power on top end, current top speed of vehicle not towing anything approx 80-85mph on level ground with pedal floored


History:
Fuel pump total failure approx 3 mos ago, replaced with aftermarket pump assy (1 piece in tank version), approx 1 month ago, truck would not get out of 2nd gear, tach was very high, speed was low, engine was making low power, found problem was corroded distributor cap and wire ends, replaced cap, rotor, all wires, and plugs with Bosch platinum +4 plugs (first time I have used these in this truck)

Diagnostics so far:
Fuel pressure at rail, with engine not running 25-40psi after system primes
Engine running approx 25psi at idle, high idle (3000rpm) 28psi
Turn on engine, prime system to 40psi, do not start, after 10 mins, pressure drops less than 5psi

Thoughts:
I was fairly convinced the problem was fuel delivery (possibly a cheap aftermarket replacement fuel pump) until I saw the starting problem while monitoring pressure on the fuel rail, had trouble turning over at 35psi on the rail after sitting 2 hrs. I have heard people telling me spark problems, now I am not sure. The only really new thing I have never used on this truck were the Platinum +4 plugs, I have always used bosch platinums in the past. Does anyone have any experience with these plugs?? After installing the plugs, the truck started fine for several weeks, this starting problem only showed up about 2 days ago. Everyone keeps saying change this/change that (for everything from fuel injectors to ign coil), but I really prefer troubleshooting over guessing. Any ideas?

 

Hello, I have a 1991 Ford bronco. It has 240,000 on it now. I have had similiar problems but replaced it with a stock Ford fuel pump because I have had such poor luck with after market parts in the past. I bought it in 1999 w/176k. It sounds like you may need to try replacing your fuel regulator. However before you replace even one more thing you first need to buy a code reader. I have one and they are cheap and very effective How does $35 sound. So far mine has never been wrong. This little tool will save you hundreds if not thousands of dollars. Depending on how many yrs. you plan on owning this thing. And the regulator is a quick easy fix. GOOD LUCK!
But I think your almost there if buy the code reader.

 

Ok. First of all have you looked for codes? Do that FIRST. They might save you a lot of hassle, time and money by pin pointing any problems.

What have you gapped the plugs to? Is it within spec? Have you still got the old plugs? Try putting them back in (assuming they are not broken) and see if tis better.

Can anyone else confirm fuel pressure? My truck is in the shop at the moment so I can't go measure mine to compare.

Start with codes and see where that leads ya.


Simon

 

Found on the autozone site:

The pressure regulator reduces fuel pressure to 39-40 psi (269-276 kPa) under normal operating conditions. At idle or high manifold vacuum condition, fuel pressure is reduced to approximately 30 psi (207 kPa).

http://www1.autozone.com/servlet/UiB...3d800a3625.jsp

 

It sounds like mucky paws has just found you 5psi. worth of problems just to start.

 

This is what ya need to buy:
http://www.midwayautosupply.com/deta...ption.asp?3829

Best $34 I have spent and even with the shipping to the UK its cheaper than 1/h at the shop for someone else to pull the codes.

(I'm sure there are other suppliers so please please try the sponsors of the site first - most of them don't ship to the UK so thats why I had to go to Midway)

 

I have a snap on mt2500 scanner, no Key on Engine off codes or key on engine running codes being generated. As for the pressures I quoted they are within spec (25-45 psi system primed engine off, 20-40psi running). With stable pressures on the rail, especially when snapping the throttle, combined with the fact that the rail pressure does NOT dramatically drop when the engine is turned off (bad check valves in regulator), it seems the fuel regulator is good, and engine vacuum is ok. Good questions about the codes, sorry forgot to mention it.
Thanks
Brian

 

I'd go back to the plugs or ignition then.

You could also try disconecting the battery power for a while (>20 mins) to reset the ECU and let it retune itself. Might work but I admit I am starting to guess now.

Simon

 

prob best to wait until Greystreak comes online later - he's the guru!!

 

i believe the fuel pressure is too low at idle. It should be around 34 or so if i remember correctly. I know on both an f250 and my bronco the fuel pressures were at least 30+ idle.

 

Remember, it is idleing very smooth, the problem occurs at startup, where the system is fully pressurized (40psi), pressure at the rail is not the problem, it is not airbound. I doubt the ecu is causing the problem, I was originally thinking fuel, but I keep going back to spark. Does any one know if the bosch plat+4's have a larger gap (hotter spark) and require more voltage to fire??? MSD coil may be in order. The clue is that it does it when sitting for a while (which originally led me to fuel), but could also be spark, when cylinders are cold, and cold gas is sprayed in during inital start, I figured demands on the ignition system are high. Push comes to shove I really don't know. One thing I found out this morning is the problem is intermittent, didnt do it initally this morning, but after getting to work and going out to lunch 3hrs later it did happen, crank time before engine fired was approx 4-5seconds, as opposed to the normal 1 second.
Thanks
Brian

 

Ok, just read the entire thread here... you say there are no KOEO or KOER codes being generated... I am assuming that means no codes indicating a fault anywhere. (Code 11 or Code 111 should be present if there are no fault codes). Its an educated guess at best then that I would offer. Might try a coolant temp sensor swap. If its "sticking" at its normal op. temp. output, the EEC computer may not necessarily recognize this as being any MISinformation since normal op temp is not "outside established parameters" so it may not trigger a fault code. If the ECT sensor is telling the computer that the engine is already at op temp, the ECM is leaning out the fuel/air mixture severely for cold starting operations. So the ECM may actually be reduing your fuel pressure and narrowing injector pulse width because it "thinks" the engine is already warm.

Again, this is a carefully considered GUESS. But given the symptoms and the fact that its an intermittant problem that rears its ugly head only when the engine is cool, its stands to reason. Keep us informed.

 

Welp, that is definately a good well thought out answer, Its one I certainly never even considered. I seem to be very focused on the ignition system right now. I assume on the scanner there has to be a way to read that sensor on the data scan. most importantly, Where is that sensor located????? What is its normal resistance at cool temps, I will replace it with a fixed resistor to simulate a cold engine condition, and attempt to duplicate the problem. As it stands right now I am leaning toward trying a TFI module, only problem is usually the TFI module is mounted to the side of the distributor, yet all I see is a harness coming out the side of my distributor, no module anywhere, could it be inside the distributor in a 94?? or mounted elsewhere in engine compartment? I have found the time it takes the problem to reproduce is approx 1-2 hours of sitting since shutdown, any sooner and it starts fine, maybe some slight hesitation after 1/2hr, but certainly not 4-6 seconds of cranking. Upon shutdown, immediate hot restart is perfect.
Thanks
Brian

 

My problem wasn't the same as yours but my experience with Bosch plugs was horrible. When I first bought my Bronco I did a tune up. Cap, plugs and wires. I used the Bosch plugs. It ran fine for about 200 miles and then started missing. I pulled the plugs and found that the #8 cylinder plug had burnt off the entire end from the threads down. I bought a new plug, checked the gap and reinstalled. At 150 miles same problem. My dad is a Snap-On dealer so I had him check with several mechanics. They all said to change the plugs to autolites. I did and have about 8,000 miles on them without any problems. Some people will say they are great plugs but my experience was pretty lousy. I agree that greystreak has a well thought out theory to your problem but if that doesn't work you may want to look at your plugs. They are cheap and not to hard to change.

 

It looks like the TFI module is part of a heatsink on the driver side fender, are these prone to failure like the distributor mounted version?? What else can cause a intermittent hard start overnight (not something that has been getting gradually worse)??? I will definately explore the coolant temp sensor, but I would think this would be a problem in the winter, not necessarily when it is 85deg outside. And just looking at the design it looks like it is more prone to fail the other way, because high temps equal low resistance, if the sensor were starting to open for whatever reason (dirty connectors, cracked thermocouple joints, etc) it would go high resistance, hence fooling the engine into believing operating temp was lower than normal.

thanks
Brian