Hot Start Problems

[beemer]

The '95 does not have a crank pos sensor, I mentioned above, for ignition issues there's excellent diagnostics in the rave manual

If your truck runs ok most of the time & has spark when it won't start, then it's a fuel issue.

If you have a schraeder (tire type) port on driver's side fuel rail, you can borrow a buddy's
tire gauge & check fuel pressure as someone turns on the key

I used my wife's gauge.
(35# @ idle)

luck,greg

You should hae a reading from 2.4 to 2.7 bars pressure not the standard of 3 bars or 43.5 PSI. This explains why they use 24# injectors that can feed a 351" Ford or a 260 HP 5.4 litre SOHC truck motor.

 

[beemer]

The '95 does not have a crank pos sensor, I mentioned above, for ignition issues there's excellent diagnostics in the rave manual

If your truck runs ok most of the time & has spark when it won't start, then it's a fuel issue.

If you have a schraeder (tire type) port on driver's side fuel rail, you can borrow a buddy's
tire gauge & check fuel pressure as someone turns on the key

I used my wife's gauge.
(35# @ idle)

luck,greg

That would be on the right side of the fuel rail for the schraeder valve fitting not the left unless you can reach under the ram tube base and plenum on the left going after the fuel temp sensor. A 15 year 95 D1 owner here, 4.6 no engine part has gone untouched without a mod or improvement, room for plenty of them.

 

[KonaCrash]

Aloha everyone.

So I switched out the fuel pump relay. Didn't seem to help. I took the old fuel pump relay and put it into the main fuel relay slot and left the new relay in the fuel pump relay to test the main relay. Results are inconclusive so far on that.

Haven't gone out and bought a fuel preasure tester yet. I tried using the tire gauge and just got a nice spray of gasoline all over, so I might have to just spend the $50 for the real gauge.

One other idea that came to mind that I want to bounce off you all. Could I possibly have a bad Vehicle Speed Sensor? This is what it says in the service manual:

The vehicle speed sensor is located on the side of the Transfer box adjacent to the parking brake. The sensor provides road speed data to the ECM. The ECM in turn detects vehicle movement from the road speed input and ensures that idle air control mode is
disengaged. ***Should the vehicle speed sensor fail in service the ECM idle air control would become erratic.*** The sensor also provides road speed data to the
electric speedometer and cruise control ECU.

So if that could make the idle air control messed up, could that be my problem? Something else to note is that my cruise control also does not work. (never worried about the cc not working because I live on a small island.)

A second alternative to consider: the throttle position sensor. Again the service manual:
The throttle position sensor is mounted on the side of the plenum chamber inlet neck and is directly coupled to the throttle butterfly shaft. The throttle position sensor is a resistive device supplied with a voltage from the ECM. Movement of the accelerator pedal causes the throttle valve to open, thus rotating the wiper arm within the throttle position sensor which in turn varies the resistance in proportion to the valve position. The ECM lengthens
the injector open time when it detects a change in output voltage (rising) from the throttle position sensor. In addition the ECM will weaken the mixture when it
detects the throttle position sensor output voltage is decreasing under deceleration and will shorten the length of time the injectors are open. When the throttle is fully open, the ECM will detect the corresponding throttle position sensor voltage and will
apply full load enrichment. This is a fixed percentage and is independent of temperature. Full load enrichment is also achieved by adjusting the length of
the injector open time. When the throttle is closed, overrun fuel cut off or idle
speed control may be facilitated dependant on other inputs to the ECM.
The throttle position sensor is ’self adaptive’, which means that adjustment is not possible. It also means the throttle position sensor setting is not lost, for
example, when throttle stop wear occurs.

So if the throttle position sensor depends on resistance to function properly, could the copper wires that are exposed coming out of the TPS cause a change in resistance when exposed to heat and thus not allow the TPS to function properly? It looks like the rubber coating of the wires has become hard and brittle after 15 years.

Sorry for another long one and thanks a lot for your comments or ideas.

Eric

 

[greg409]

That would be on the right side of the fuel rail for the schraeder valve fitting not the left unless you can reach under the ram tube base and plenum on the left going after the fuel temp sensor. A 15 year 95 D1 owner here, 4.6 no engine part has gone untouched without a mod or improvement, room for plenty of them.

you are correct,sir. I looked @ mine after post but was too lazy to change it.

I figured Kona would find it.

Speaking of Kona, I doubt the resistance value of the wires would change unless they were corroding or breaking.

 

[beemer]

Sorry I don't come back to this forum more than every 2-3 weeks at a time, too busy on my engine forums, home brewing and welding forums.
Leaking injectors, fuel regulator or fuel pump taking a dump, and the OMG Rovers mighty electrical problems. They may have one or two. More like 200 with water leaks causing may of these electrical problems.

 

[KonaCrash]

Okay, so I pressure tested the fuel rail. I didn't depressurize the system first or release the gas tank pressure, hopefully that doesn't matter. Here are the results:
Initial hook up: 20psi
key at 2nd position: 20psi
car wouldn't start right off since a bunch of fuel came out when I hooked up the gauge, but I took off the vacuum tube on the fuel pressure regulator and it started right up.
at idle with vacuum tube off regulator: 20psi with throttle open: 20psi
with vacuum hose back on regulator at idle: 21psi with throttle open: 21psi

I let it idle for a bit and the pressure slowly increased, after about 5 or so minutes it increased to about 24 when I turned it off. While I was letting it idle I would open the throttle once and a while and it would result in an immediate 1-2psi drop then it would go right back to where it was before opening the throtttle.

So the pressure is clearly low (I think it should be about 2.5bar or 37psi?) so that probably means the fuel pump need to be replaced. However, when the vacuum hose is off the fuel pressure regulator the pressure didn't go up at all, indicating that the regulator is bad.
What should I replace?

Thanks. Eric

 

[greg409]

If the regulator was restraining a good pump, then I'd think the pressure would rise when you pull the vacuum line.

I'm more inclined to think the regulator is wide open, the pump isn't making it, or the fuel filter is loaded.

I didn't go back & read - did you already replace the filter? have you checked the pump electrical connections on top of the gas tank?

Your fuel pressure should be in the 37# range.

If you need a pump, a common replacement is an AIRTEX #3270 - it requires minor mods (very minor) $50 - $70
I'm not 100% sure of fitment on a '95 DI, tho'
A lot good feedback

luck,greg

 

[KonaCrash]

Hey everyone. So I put in a new fuel pump on Saturday and the pressure is back up to about 35psi. I've driven it around a bit the past two days and I haven't had my hard hot start problem that started this whole thing. Although, I have had to reset the check engine light twice, but it didn't give me a fault code on the readout under the seat.

So far so good. I'll update in a couple weeks if things are still going good.

 

[greg409]

Excellent, now you're the pre'96 DI fuel pump freak.

congrats

luck,greg

 

[KonaCrash]

Alright it's been a couple weeks. The hot start problem seems to be solved by replacing the fuel pump. I actually heard someone on 'Car Talk' with the exact same problem and was hoping they would tell her to check the fuel pressure, but the had to explain how to check the spark.

Anyway, starting problem solved...however, the idle air control fault remains (fault 48). It only comes on after idling in park for a minute or two, or occassionally right at start up.
Idling in neutral or in gear with the brake on does not seem to induce the fault code and check engine light. When the fault comes on, the idle seems to go a little high when I put it into park.....goes up to about 800. Shouldn't the idle drop to say 600 when I go into park instead of going up a bit?

I think I'll be starting a new thread focussing on Fault 48.

Thanks for the help.