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I've been trying to resolve a hard-starting/rough idle/stalling issue on my 91 econoline with a 4.9L I6.
Vacuum seems to be good - holds steady around 25in. I think the vacuum reservoir (coffee can) is bad since the vacuum out is only 10in or so and the vacuum in is around 25in...or is this by design? I took the coffee can out altogether while testing other things to remove it from the equation.
In the last few months I've replaced:
- few vacuum lines that were in bad shape.
- EGR valve and position sensor - old units were definitely bad - old EGR valve was completely blocked and corroded shut
- Throttle position sensor - resistance jumped all over the place while testing it
- Idle air bypass valve
- MAP sensor - seemed to run better without the vacuum line attached to it, but the new unit doesn't seem to work much, if any, better than the old unit. so maybe the old unit is good after all?
- iginition coil - the post on the old unit was badly pitted
Also cleaned the distributor cap and rotor contacts. Ran the engine in the dark and didn't see any arcing.
Within the last 5k miles I replaced the dist, wires, and plugs.
Fuel pressure check:
Last night the pressure didn't seem to build with the key on, engine off, although I did hear the pump running. Cranking the engine several times finally got it running, fuel pressure was around 45-50 PSI. Once the engine finally starts it will not keep running unless I pump the gas. It will run for 20-30 seconds, then sputter out. It's better when it warms up and will sometimes run for a minute or two before shutting off.
After warming up the engine I unhooked the vacuum supply to the fuel pressure regulator from the vacuum tree. The idle increased but smoothed out, fuel pressure rose to about 60PSI. If I plugged the now-open vacuum port, idle settles back down but the engine runs rough, but the engine does not stall. Just keeps on running. Plugging the vacuum supply to the pressure regulator drops the fuel pressure back down to 45PSI and the engine will eventually stall again. Makes me think it's the regulator? Or is the fuel pump not supplying enough volume?
I left the fuel pressure gauge on over night (was 50PSI at 9:00PM) and this morning at 9:00Am it was zero. Seems to stay pressurized for at least 15-20min though. How long should it stay pressurized? This morning though the pressure built to 40 PSI with KOEO. Turned ignition off then back on (but didn't crank the engine), pressure built to 50PSI.
KOER codes yield (looks like a few more things to address...):
126 - Manifold Absolute Pressure (MAP) or Barometric Pressure (BP) signal values higher or lower than expected (with NEW MAP sensor)
172 - HEGO indicates lean
225 - Knock Sensor (KS) signal not detected during Dynamic Response Test (Engine Run Self-Test).
332 - Insufficient EGR flow detected. (I'm pretty sure the EGR solenoid is shot - I never get a vacuum coming out of the regulator but there is definitely vacuum going in)
412 - Cannot control RPM during Engine Run Self-Test high RPM check.
556 - Fuel Pump (FP) relay primary circuit failure.
632 - Overdrive Cancel Switch (OCS) no switch action detected during Engine Run Self-Test
Not sure how I can get a 556 if the engine is running?
Sorry to be so long-winded... thanks for any info! I've learned a lot from this forum by reading old threads.
Good post, lots of info is helpful in getting a decent diagnosis. Can you measure the voltage coming out of the fuel pump relay? If pressure jumps when you disconnect the regulator while running, then the pump is able to deliver sufficient flow. Lean mixture indicates that it is indeed a fuel problem, another way to check this is spray a can of carb cleaner in the motor when you hear it start to die, if it surges and keeps going then you can eliminate spark as a possibility. Sounds like you have it narrowed down to fuel already, but this is an easy check to verify that.
Thanks for the tips jb1390. The pressure jumps to almost 60psi when I disconnect the vacuum line to the regulator. Engine runs smooth although the idle is a little fast (maybe compensating for the extra fuel?)
I also tried spraying carb cleaner into the intake when the engine was about to die - it pepped back up and ran smoothly until it was ready to die again, so it does indeed sound like a fuel problem.
So now the question is, does it sound more like the regulator or fuel pump? I disconnected the out of tank pump to see if the in-tank was firing and I could hear it when I turned the ignition on and I could definitely tell that the out of tank pump is firing as well when I reconnected it.
I wasn't able to measure the voltage coming out of the fuel pump relay because, well, I'm not sure where it is! My repair manual says it's in a power distribution box in the engine compartment on the driver's side but I'll be darned if I can't find it...
Not sure if your pump relay has a feedback to the computer, but a primary circuit failure is something on the input side, not output to the pumps, I would think - especially if your pumps are running when they should. The box it's located in is a black box with relays and fuses in it on the inside of the fender, IIRC. If you have dual pumps (in tank and out of tank), I would think you also have two filters, one low-pressure, one high-pressure. I'm going to take a guess that the relay is not feedbacking to the computer telling it that the pumps are running - which may or may not affect injector firing, etc. 45-50 PSI should be enough - what do the specs say, or do you have a book? Did you notice any wetness in the vacuum line going to the FPR and a gas smell (would indicate a bad FPR)? What does the output of the 'coffee can' feed? A screwy MAP sensor or vacuum input to it or bad electrical connection from it will cause issues similar to this as well. The EGR issue will also contribute to this. Some of those may be operator-error related during diagnostics, but you may want to check some of the connections to things (i.e. Knock Sensor). Best bet is to eliminate the error codes one at a time until you have cleared them all.
-1987 Bronco II XLT 2.9L V-6 5-Spd 4x4 'xplorer coils & leafs, MT/R 30x9.50s, 2 1/2" cat-back
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-1994 Chevy 2500 5.7L 5-speed
"Did you notice any wetness in the vacuum line going to the FPR and a gas smell (would indicate a bad FPR)?"
I didn't notice any gas (or other moisture) in the vacuum line going to the FPR.
"What does the output of the 'coffee can' feed? A screwy MAP sensor or vacuum input to it or bad electrical connection from it will cause issues similar to this as well. The EGR issue will also contribute to this."
The coffee can feeds the EVR solenoid and the air bypass solenoid at the back of the engine. I haven't noticed any difference with or without the coffee can in place.
Some of those may be operator-error related during diagnostics, but you may want to check some of the connections to things (i.e. Knock Sensor). Best bet is to eliminate the error codes one at a time until you have cleared them all.
If I get a few minutes this weekend maybe I'll run the KOER test with the FPR disconnect and see if I still get a lean condition. I'll also check the knock sensor connection...
Start by checking the fuel pump relay. When the engine dies does it hop up and down looking for idle? That would idicate a vacum leak. Testing for vacum leaks is a can of ether and some patience.
Deleting your computer can cause these symptoms as the computer is frying its developed program. Deleteing it sends you straight back to the factory program.
Id try the fuel pump relay first. Clean all the contacts in the relay board. A pice of emery cloth pushed in with a small screwdriver works ok.
Im not sure if the 91 still had the two stage fuel system. Check all your filters, look for leaks.
Try her then. No luck test for vacum leaks. Next check for bad wires. I mean fan em out and look for burns, cuts, and cracks.
556 could throw as a memory code. Can you keep her running by adding throttle?
I *think* I've done a pretty good job searching for vacuum leaks. I replaced a few lines and tested as many as I could find. In addition to basic testing I've tried unhooking just about every vacuum line from the vacuum tree and the only one that really makes a difference is the one to the fuel pressure regulator.
I can keep the van running forever by feathering the gas pedal. It seems (after my testing last night), that can also keep it running indefinitely by spraying carb cleaner into the intake through a vacuum hose.
That suggests a problom on the fuel injection circuitry, or a vaccum leak. Try spraying your carb cleaner around all the joints in the intake system. I belive the 91 EFI was still speed density. If its MAF or VAF I'd check your sensor.
These EFI probloms are a bugger to find but with persistance and a friend to rant about the pos, you'll get her.
If anyone can upload the 91 econoline 300 EFI diagram from a chiltons or haynes it would be a big help to me for helping eyancy out.
Once agin I'd check for vaccum around the intake manifolds.
Note. You can totaly disconect your EGR without any issues I've done it on several vehicles. The idiot light will flash, but thats all.
Based on the diagrams you sent and my fuel injection book your EGR may be stuck open. That is a guess. When trouble shooting these vehicles it is a game of chase the white rabbit.
First lets test your MAP sensor. Youll need to have a multitester.
There are three wires going into a MAP sensor on a ford one is a reference voltage going back to the sensor, one is a power wire, and one is a ground.
blk/wht is my guess for a ground wire.
org/wht is my guess for the power wire sould be aprox 5V +/-0.2V
LtGrn/blk sould be the refrence wire it sould be 2.5V
The EGR position sensor, MAP, and Throttle position sensor all share the same ground and power wires on a 91 4.9 pkup. Check for bad connections there or broke/ burnt wires.
I'm going to tell you agin to go crazy and check every vaccum leak posibility at least three times. I personaly have spent 8 hours chasing a rabbit code to find the problom. A vacum leak.
A very good book that I picked up is How to tune and modify, Ford Fuel Injection, By Ben Watson. Has a brief breakdown of all the codes, Sensor testing, and most likley cause. I picked mine up for $12 on amazon used.
His most likely cause For the MAP problom is a stuck EGR. A bad wire on any of these or a vaccum leak can cause all of this to happen.
Good luck thanks for the diagrams, and if you neeed more help I'm on a layoff status so have tons of time to help.
Thanks for the suggestions. As for the MAP tests - do you just turn the ignition on and then test the wiring harness, or is this something that needs to be done while the engine is running?
I checked some this evening for vacuum leaks - still haven't found any...of course the front of the engine is hard to get to in the van so there could be something there that I just can't get to.
This weekend I'll try to check the grounds you mentioned and maybe pick up a new EGR/EVR solenoid - mine doesn't seem to be operating based on a quick test I performed by taking the unit out and applying voltage to it. The voltage going to it seems to be fine. If I open the EGR manually by sticking a screwdriver in it's definitely letting exhaust gas in and seems to even back out if I close it.
I found the fuel pump relays and cleaned the contacts - didn't seem to help. I tested the voltage on the fuel pump test lead and got less than 12v - should there be 12 or 12.5 I wonder? When grounding the lead the fuel pumps fired right up.
In case it helps, when the engine heats up it runs pretty well - it ran for at least 5 minutes *with* the FPR connected. If I turn it off and then immediately turn it back on it seems to hunt for idle and then will smooth out and run well. Then, out of nowhere, it'll start hunting again but it usually stays running.
Thanks again for all of your help and time. Hope your layoff status is short-lived (unless of course you want it to be longer!)
See if the fuel pressure in the "log" drops or dances about when its experiencing rough idle/ death mode. You can do an idiot test on the relay by feeling if it gets abnormaly hot. Just compare the temp on the relay to another relay that is operating when the engine is running.
Your problom seems simaler to one I encountered a few years back. Turned out the problom was in the TFI modual on the distributor. After I tested everything in the fuel system. The thing shot codes for everything. Turned out the ignition was just 20yrs old.
Actually, now that you mention it, last night I happened to glance over at the fuel pressure as it was starting to die and the fuel pressure had dropped to 40 (from 45) and then shot back up over 50 or so I think. I'll see if I can get the timing of those events more exact. I'm not sure if the pressure dropped before or after the engine started sputtering so I couldn't say if the fuel pressure drop is a cause or symptom of the issue.
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