Troubleshooting - Hard starting when hot

Hi,

Talking about a 1993 Ford E350. Gas engine. 5.8L V8 351.

To keep this shorter, I'll skip a lot of details, and try to hit the highlights.

Starting last summer, this truck / van began having hard starting problems. Never when cold, but happens when hot, especially after long driving.

I've been told that it's a fuel system problem. The fuel filter was changed, with no improvement. Then I had a pressure gauge put on the fuel system, which showed a fuel pressure leak. Starting somewhere around 70 PSI, I'm told it should lose 5 to 10 PSI in about 10 minutes and still be normal. In roughly that amount of time, mine dropped down to about 20 PSI. Not "by", but "to" 20 PSI.

The mechanic who did that pressure test told me that he thinks it's a bad check valve on the fuel pump. He recommended replacing the fuel pump. I haven't done that yet because I'm not convinced it's the fuel pump, knowing the pump was replaced 3 years ago, with very little mileage put on the vehicle since then (10-15K).

My current dilemma:
I don't know whether the problem is the fuel pump or the fuel pressure regulator, or some other part of the fuel system that might be leaking pressure. I don't want to replace the fuel pump just on a hunch as it is expensive and very time consuming. 

As for the other option, although it only costs $20, the fuel pressure regulator is a severe pain in the ass to get to, seeming to require a special tool or some type of articulated allen wrench.

If anybody has any ideas that could help me _easily_ determine which part is faulty, so I don't waste time, effort, and money, I'd really appreciate it.

My only clue comes in the form of answers (which I don't have) to two questions:

1.  It would seem to me that either the fuel pump, or the pressure regulator, or both, or neither, would align with the symptom of hard starting when hot. Just logically, how could a faulty check valve on the fuel pump affect starting only when it's hot, rather than at all times?

2. Is it logical that only one of those two parts, while going bad, could still last for 7 months and over 5,000 miles? If not, this may be something else like a fuel injector or bad timing.

Thanks for any help you can give,

Tom

so the starter turns over fine but it won't start? start eliminating you fire triangle. is the spark ok when hot? if it is shoot some quick start down the intake when it happens, does it fire? if it does it is fuel issue. highdesertranger

Not a bad injector or timing, that is clear.

Could be as simple as the fuel in the lines are being boiled by the heat of the motor, cause air bubbles in the lines (and low pressure because of the bubbles). I’ve had that same problem for years on my older car. You could test that theory by insulating those lines running close to the engine itself to see if it helps.

Otherwise I would second the fuel pump or regulater causing a release of pressure after it is heated up. Start with the least expensive (pump or regulator) and give it a go.

Thanks for the replies.

HDR:
It always starts, it just takes longer and sometimes sounds like it's not going to start when it's hot. The engine is fuel injected, so I normally don't step on the gas while starting. But if I step on the gas while it's having this starting problem, that helps it start. The plugs and wires and distributor were replaced in the last year. The battery, starter, and alternator have been checked twice by the little electronic gadget at auto parts stores, about six months apart. All passed both times. The engine seems to run very well, it just has this hard starting problem.

VT: You said, "Not a bad injector or timing, that is clear." How did you rule those two things out?

Tom

try this, get it hot enough to were it does the hard starting. then shoot some Quick Start down the intake after the air cleaner. if it fires then you have a fuel problem. have you tried to turn the key to run and off several times before trying to start it? this will prime the fuel system. highdesertranger

If the injectors or timing was bad, it would hard-start every time, not just after hot.

Your further explanation does sound exactly like a fuel-boil problem. This is actually very common among EFI vehicles. The way the factories eliminate the issue is to have an electric   fuel pump pressurize the system the moment you turn your ignition key a single click towards start. You should be able to hear that happening. If it is failing to pressurize (bad pump or reg) then it can not feed enough fuel to the motor to get it started where the engine-driven fuel pump can take over and feed more fuel to the motor. Basically the electric fuel pump is solely to remedy the hard starting and does not sound like it is functioning properly. Click your key forward one click and listen for the fuel pump. It could be bad or even just as simple as a loose wire

It should be a simple job for you to do on your own ( if the pump is external of the tank). You may want to pickup some new fuel line and replace what you can as well, just to eliminate any possibility of a crack in any of them

I have the same '93 Ford engine and also have this problem but it's not that bad. It also runs a little rough after warming up and I will eventually replace the EGR valve and IAC since all these sensors are 25 years old. They all affect how the fuel/air mixture is adjusted by the computer.

Have you checked for codes? The fact that partially depressing the throttle helps it to start seems like there may be a problem with the Throttle Position Sensor but supposedly it would throw a code if bad. I've spent quite a bit of time on Ford forums and there are several poor performance related problems similar to this that don't throw any codes, so it's frustrating.

I'm suspecting the Engine Coolant Temperature Sensor on my van.The Haynes manual shows how to test it for resistance but I will probably just go ahead and replace mine as a Motorcraft sensor from A-Zone or O'Reillys is about $35.

I'm not sure if this engine has an Air Charge Temp Sensor but that would be suspect as well.

HDR:
You asked, "have you tried to turn the key to run and off several times before trying to start it?"  Yes, and that was also recommended by the mechanic who thinks the check valve on the fuel pump is bad.  However, I've not noticed that doing so (either once, or twice, or waiting longer after doing it before starting) helped at all.  That gave me another reason to doubt the fuel pump as the problem, because the quick "fix" didn't seem to fix anything.

=====

VT:
Thanks for explaining.  Didn't want to muddy the waters with even more info initially, so here are the only other clues that I have.  Might be revealing, might not. The vehicle had a very bad pinging problem originally, only noticeable under load (like climbing hills).  For that reason, etc., a more experienced person helped me adjust the timing manually, with a timing light (even though a sticker on the engine says not to adjust it manually, but let the computer do it).  The timing adjustment completely eliminated the pinging issue (which had made the vehicle useful only on flat ground), but either immediately or about that time, the occasional hard starting problem appeared.  Prior to that adjustment, I never had this hard starting problem.  Might be a coincidence.  Just based on the time of appearance, I had to wonder if the timing adjustment could be related (maybe adjusted too far).  Someone on another blog also mentioned timing related to another guy's similar problem.  All that said, I agree that a timing problem _should_ logically affect starting at all temperatures.  As for the fuel injector, probably the same, but I don't know enough to say.

Regarding the fuel pump, trying to follow you, but I got a little lost about the different types of pumps.  Are you saying 1) that I have two fuel pumps, or 2) I need to add an auxiliary electronic fuel pump, or 3) just that I need to determine which I have, or 4) just explaining the way the standard set-up works?  The new fuel pump that is supposed to replace the current pump is one made by Delphi (Part #EFG0946) for a fuel tank located completely behind the axle.  That fuel pump (curse all automotive design engineers) is thoughtfully located inside the fuel tank.

Also, do you think, if this is the fuel-boil problem, that it would just suddenly appear, vs. always being present on this vehicle?  Seems like the latter _should_ be the case, but I'm only guessing.

=====

slow2day:
Thanks for the info.  In a goofy way, it's nice to know that someone else is struggling with the same thing.  You asked if I checked for codes .  Yes, frequently (OBD-1 code reader for Ford).  Codes, but none related to the components you mentioned.  The only persistent code is one related to the HO2S / O2 sensor showing lean conditions.  Code 172 as I recall.  Had the system smoked recently for vacuum leaks.  Found one hose, fixed it.  (EDIT:  Didn't solve the problem). Might be one more leak related to exhaust.  Haven't fixed it, but that is unrelated to this hard starting problem.

Have any of the changes that you've made to your engine either fixed or lessened this hard starting problem?

Tom

Vagabound said:

slow2day:
Have any of the changes that you've made to your engine either fixed or lessened this hard starting problem?
Tom

Click to expand...

Well, I've driven 3600 miles in the past 1-1/2 months and the van basically run OK. It was tuned up right before I left and the only other thing I've done is add Seafoam twice. It really did seem to help but only temporarily. I was tempted to have a shop clean the injectors but haven't.

It's too cold where I'm at now, so I'll have to wait before I can do some more testing or parts replacement. I'll be sure and post any improvements.

I don't see how the engine timing would cause a loss of the fuel pressure, and again, it would happen for every start, not just once it is hot. The fact that this happens ONLY when the motor is hot, and turned off for a bit, says to me that it is the fuel-boil issue. I assume once you allow the engine to cool for enough time, it starts fine again? 

The correct term for this problem is Vapor Lock and well documented. I have had this problem for years on my Datsun 280z. That car has the two pumps, one specifically to cure the vapor lock issue. Your van may not since it has an internal (to the gas tank) pump. You may have a hatch on the floor inside the van to access the pump, otherwise you have to drop the tank and replace the pump that way... a little more difficult, but otherwise still a fairly easy procedure.

The good news is that it is not a fatal issue. You can simply work around it for now until you have more time/cash to deal with it. Just pan to hang out for a few more minutes after you run into that store... or leave it running if it is a quick in and out. Popping the hood to allow it to cool quicker will help too.

Good luck

Van-Tramp said:

... says to me that it is the fuel-boil issue. I assume once you allow the engine to cool for enough time, it starts fine again? ...

Click to expand...

Yep, that's right.  It's most obvious after it's been off overnight.  I don't think I've ever had the hard starting issue on the first crank of the morning.

Thanks for all the good info.

Tom

What are the ambient air temps where you are now?

slow2day said:

What are the ambient air temps where you are now?

Click to expand...

Low 80's daytime, and 50's at night. That said, this problem has existed for almost 10 months, through numerous states, seasons, and climates.

Tom

This is a common problem with a number of FI vehicles. I had an F250 4x4 that had the same problem. Took me near forever to find the problem, searching the net and asking questions at auto shops. Kept hearing the same things over n over (fuel pump, injectors, brain box). Finally stumbled upon the solution cruisin the net. I'm not saying that your problem is necessarily this, but there's a good chance.
Turns out that there are 2 thermostats screwed into your engine. 1 goes to your gauge and is of no import. The second which, if I remember correctly, screws into the base of your intake manifold on the drivers side is connected to the ECU and is VERY important. After a while they go 'out of range' and the ECU can no longer meter fuel correctly. This screws up the whole works and you end up with an incredibly rich mixture when you try to start, akin to flooding a carbureted engine. Often, people replace these wwith a cheap Mexican temp sending unit and they often fail- get the brass OEM one. If you look in a repair manual, it'll show how to test yours with a multi-meter. If it IS your problem, it's a 10 min fix if you have the part and correct size deep socket. ..Willy.

Hi Willy,

That's an interesting idea, thanks. A couple of questions:

If that thermostat is broken, and it essentially floods the engine, wouldn't that problem be present and obvious during cold starting as well as hot starting?

The only remaining code that I'm getting from the engine is one that I've gotten for quite a long time. I mentioned it above. But it relates to the O2 sensor thinking the engine is running lean. That could be for a different reason, but almost seems to point in the opposite direction. What do you think?

Something else to check.

Tom

Willy has a good idea there. when the engine is cold a super rich condition helps the engine start. that's is what a choke does, blocks off the incoming air to create a super rich condition. with a good code reader it will tell you the temp the computer is seeing. highdesertranger

Willy said:

....The second which, if I remember correctly, screws into the base of your intake manifold on the drivers side is connected to the ECU and is VERY important. After a while they go 'out of range' and the ECU can no longer meter fuel correctly.

Click to expand...

This is the Engine Coolant Temperature Sensor I mentioned earlier. The resistance is high when cold and decreases as temp rises. It can be checked w/meter but access may be tough (see p.6-16 of Haynes). Also check post #19 on this thread:

https://www.ford-trucks.com/forums/1156379-1994-351-fuel-pressure-test-fail-2.html

Also, Willy is right about buying aftermarket sensors....many are junk. You can get the Motorcraft part on Amazon:

https://www.amazon.com/Motorcraft-D...d:e-150+econoline&refinements=p_89:Motorcraft

PS: I will soon post a pic of the diagram and location.

Here's a diagram of the location from the FSM. The arrow points to where the Temp Sending Unit for the gauge would be in the thermostat housing. Also, the MC part seems to need a change in the connector. I'm not sure right now what's involved but did see this mentioned on the Amazon reviews. Plus the pic there shows a pigtail that is included.

BTW: You will see on forums the computer referred to as ECU or PCM or even ECA (Electronic Control Assembly). It can be confusing. The factory manual calls it the Powertrain Control Module.

highdesertranger said:

Willy has a good idea there.  when the engine is cold a super rich condition helps the engine start.  that's is what a choke does,  blocks off the incoming air to create a super rich condition.  with a good code reader it will tell you the temp the computer is seeing.  highdesertranger

Click to expand...

 Wut he said. ..Willy.

Let me see if I can summarize this idea about the coolant temperature sensor and ask a few questions to clarify this.

First, thanks for all the good info and diagrams and links. Very helpful.

Summary: Let's say this sensor / thermostat is malfunctioning. It seems that everyone is saying that would make the fuel condition too rich. Too rich when the engine is cold is okay because that simulates choke conditions and helps starting. However, too rich when the engine is already hot does something bad, presumably causes the hard starting symptoms that I have experienced.

1. Is my summary description above correct? If not, what do I misunderstand?

2. Logically, how could a device that reads engine coolant temperature affect the fuel system? My only guess is that engine coolant temperature is a proxy for engine temperature which may be needed by the computer to adjust the fuel mixture. Is that right?

3. The vehicle seems to run fine once it's going, with the possible exception that is gets worse gas mileage than I think it should be capable of. About 6-7 city, and 8+ mpg on the highway. Fully loaded. On the other hand, some people have said that's normal for this vehicle. 

That is only background to ask this question: it would seem to me that if this sensor is bad and it's constantly making the engine run rich, wouldn't that affect more than only starting when it's hot? Shouldn't it also run poorly all the time?

4. From the diagram I still can't tell where that doohickey is located. If anybody already knows where to look to find it, please let me know. Otherwise, I'll go off hunting.

Thanks a bunch for all the good info so far.

Tom