- Joined
- Aug 15, 2026
- Messages
- 1
- Points
- 1
- City
- Endwell
- State - Country
- NY - USA
- Vehicle Year
- 1993
- Vehicle
- Ford Ranger
- Drive
- 4WD
- Engine
- 4.0L
- Transmission
- Manual
- Total Lift
- Stock
- Total Drop
- N/A
- Tire Size
- 265-55-15
1993 Ranger 4.0 OHV — Cold Start Stalling + Fuel Pressure Takes ~20 Seconds to Build
I’m hoping some of the 4.0 OHV experts here can help me figure this one out.
Truck:
1993 Ford Ranger XLT 4x4
4.0L OHV V6
5-speed manual
Approximately 116,000 miles
Main symptom
The truck has a cold-start problem.
When the engine is completely cold, it will start, but almost immediately wants to stall. If I give it a small amount of throttle, I can keep it running.
After roughly 30 seconds or so, it generally reaches the point where it can idle without me holding the throttle open, although the idle may still be somewhat rough.
Once the engine has been running/warming up, the problem becomes much less severe.
I’ve also noticed for quite a while that the exhaust smells strongly of gasoline, like the engine is running rich. The truck itself can also make the garage smell like gasoline, even when it hasn’t been run recently, although I’ve never found gasoline dripping underneath it.
The fuel-pressure behavior seems like the biggest clue
I’ve now tested fuel pressure at the Schrader valve on the fuel rail, and what I’m seeing seems very abnormal.
On a completely cold start, the fuel pressure was only around 2–3 PSI when the engine actually started and began running.
Yes, the engine actually started with the gauge showing only a couple PSI.
Once the engine started, the fuel pressure did not immediately jump to normal running pressure.
Instead, I watched the gauge slowly climb over approximately 20 seconds:
~2–3 PSI → gradually increasing → eventually reaching approximately 28 PSI
The really interesting part is that while the fuel pressure was slowly climbing, the engine was simultaneously struggling to stay running and trying to stall.
This was a cold engine that had just been started.
So the sequence was basically:
Cold start → engine starts with only a couple PSI showing → engine struggles/tries to stall → fuel pressure slowly rises → after about 20 seconds pressure reaches ~28 PSI → engine gradually becomes more capable of staying running.
That correlation is what has me focusing heavily on the fuel-delivery system now.
This was not a situation where the gauge simply read 28 PSI immediately after startup. It took approximately 20 seconds of the engine actually running for the rail pressure to work its way up to 28 PSI.
The pressure seems to be building slowly rather than the pump immediately producing normal rail pressure.
I’ve used two different fuel-pressure testers because the first gauge’s readings seemed so strange that I initially assumed the tester had to be defective.
With the first tester I was initially seeing essentially zero pressure despite the truck being capable of starting.
I bought another tester because I didn’t trust that result.
Fuel definitely reaches the Schrader valve, and the tester is depressing the valve because fuel comes out when the tester is disconnected.
The latest test showing the pressure gradually climbing from only a couple PSI to about 28 PSI is what really got my attention.
Fuel pump electrical testing
I’m also investigating whether the fuel pump may not be receiving full voltage.
During one test with the engine running, I measured approximately 6.85 volts while trying to check the fuel-pump circuit.
I’m not yet confident enough in how that measurement was taken to say that the pump itself is definitely only receiving 6.85V. I still need to verify the measurement directly and make sure I have a known-good ground/reference point.
So I’m not calling this a confirmed low-voltage condition yet.
However, if I confirm that the pump really is receiving substantially reduced voltage, it would obviously be very interesting in light of how slowly the fuel pressure builds.
I’m currently trying to figure out the simplest/reliable way to measure actual voltage reaching the pump and also check the pump ground.
IAC
The IAC was one of my first suspects because cracking the throttle slightly keeps the engine alive when cold.
I:
No meaningful improvement.
Interestingly, after initially cleaning the IAC and MAF, the cold-start problem actually seemed worse than it had been previously.
Before that cleaning, the truck would sometimes stay running after just a small tap of the throttle.
Afterward, I sometimes had to actually hold the throttle slightly open for a while to keep it alive.
Replacing the IAC with a new one did not fix it.
MAF
The MAF sensing wires were originally very dirty — black with a greasy-looking coating.
I cleaned them by spraying them with actual MAF sensor cleaner. I did not intentionally touch or scrub the sensing elements.
They looked clean afterward.
As a test, I later tried starting the truck with the MAF unplugged.
With the MAF disconnected, it started and immediately stalled. I could restart it and keep it running by holding the throttle slightly open.
I then shut it off, plugged the MAF back in and restarted it. At that point it was able to idle on its own, although somewhat roughly.
However, the engine had already been running for a minute or so by that point, so it was no longer a true stone-cold comparison.
ECT sensor
I suspected the Engine Coolant Temperature sensor because the problem is strongly temperature dependent.
My thought was that if the PCM incorrectly thought the engine was already warm, it might not command the appropriate cold-start fueling.
Rather than trying to accurately resistance-test the old sensor, I replaced the ECT with a new sensor.
I also cleaned the electrical connector with automotive electrical contact cleaner, blew it dry and used dielectric grease before reconnecting it.
Replacing the ECT made no noticeable difference.
Electrical connections
While working on this, I cleaned the electrical connectors for the:
I used automotive electrical contact cleaner, blew the connectors out with compressed air, applied dielectric grease and reconnected everything.
No improvement.
Spark plugs
I also removed the old spark plugs.
The plugs had dark deposits on them, which seemed consistent with the other indications I’ve had that the truck may have been running rich rather than obviously lean.
The gasoline smell from the exhaust has been noticeable for months.
Fuel-pressure regulator
I pulled the vacuum hose off the fuel-pressure regulator.
The vacuum hose/regulator connection did smell like gasoline.
That initially made me suspicious of a ruptured FPR diaphragm.
However, I checked more carefully and could not find any actual liquid gasoline.
I touched both the end of the vacuum hose and the vacuum fitting on the regulator and both were dry.
So while there was a gasoline odor, I have not found actual fuel in the FPR vacuum line and therefore don’t consider the regulator diaphragm proven bad.
Where I’m at now
The thing that seems most significant to me is the relationship between the cold-start problem and what I’m actually watching happen on the fuel-pressure gauge.
On a stone-cold start:
Engine starts at only ~2–3 PSI indicated fuel pressure.
Engine immediately struggles and tries to stall.
Fuel pressure slowly climbs instead of immediately reaching normal pressure.
It takes roughly 20 seconds to reach ~28 PSI.
As this is happening, the engine is gradually becoming more capable of staying running.
That makes me wonder whether the original “cold-start problem” is actually the engine trying to run while the fuel system is taking far too long to establish adequate rail pressure.
The possibilities I’m considering now are:
I’m especially interested in hearing from anyone who has worked on these early 4.0 OHV return-style systems.
Has anyone seen a 4.0 actually start with only a couple PSI at the rail and then take ~20 seconds of running to slowly build to around 28 PSI?
And if so, what caused it?
I’m particularly interested in whether anyone has seen this caused by a weak pump versus low voltage reaching an otherwise functional pump.
My next step is probably to get a trustworthy voltage measurement at the fuel pump/pump circuit and determine whether the pump is actually being supplied with proper voltage while it’s producing these low/slow pressure readings.
Fuel filter
I also replaced the fuel filter with a new one while diagnosing this problem.
Replacing the filter did not correct the cold-start stalling or the slow fuel-pressure buildup.
So the slow pressure rise I’m seeing — only a couple PSI when the engine initially starts, followed by a gradual climb to approximately 28 PSI over about 20 seconds — is occurring with a new fuel filter installed.
I’m hoping some of the 4.0 OHV experts here can help me figure this one out.
Truck:
1993 Ford Ranger XLT 4x4
4.0L OHV V6
5-speed manual
Approximately 116,000 miles
Main symptom
The truck has a cold-start problem.
When the engine is completely cold, it will start, but almost immediately wants to stall. If I give it a small amount of throttle, I can keep it running.
After roughly 30 seconds or so, it generally reaches the point where it can idle without me holding the throttle open, although the idle may still be somewhat rough.
Once the engine has been running/warming up, the problem becomes much less severe.
I’ve also noticed for quite a while that the exhaust smells strongly of gasoline, like the engine is running rich. The truck itself can also make the garage smell like gasoline, even when it hasn’t been run recently, although I’ve never found gasoline dripping underneath it.
The fuel-pressure behavior seems like the biggest clue
I’ve now tested fuel pressure at the Schrader valve on the fuel rail, and what I’m seeing seems very abnormal.
On a completely cold start, the fuel pressure was only around 2–3 PSI when the engine actually started and began running.
Yes, the engine actually started with the gauge showing only a couple PSI.
Once the engine started, the fuel pressure did not immediately jump to normal running pressure.
Instead, I watched the gauge slowly climb over approximately 20 seconds:
~2–3 PSI → gradually increasing → eventually reaching approximately 28 PSI
The really interesting part is that while the fuel pressure was slowly climbing, the engine was simultaneously struggling to stay running and trying to stall.
This was a cold engine that had just been started.
So the sequence was basically:
Cold start → engine starts with only a couple PSI showing → engine struggles/tries to stall → fuel pressure slowly rises → after about 20 seconds pressure reaches ~28 PSI → engine gradually becomes more capable of staying running.
That correlation is what has me focusing heavily on the fuel-delivery system now.
This was not a situation where the gauge simply read 28 PSI immediately after startup. It took approximately 20 seconds of the engine actually running for the rail pressure to work its way up to 28 PSI.
The pressure seems to be building slowly rather than the pump immediately producing normal rail pressure.
I’ve used two different fuel-pressure testers because the first gauge’s readings seemed so strange that I initially assumed the tester had to be defective.
With the first tester I was initially seeing essentially zero pressure despite the truck being capable of starting.
I bought another tester because I didn’t trust that result.
Fuel definitely reaches the Schrader valve, and the tester is depressing the valve because fuel comes out when the tester is disconnected.
The latest test showing the pressure gradually climbing from only a couple PSI to about 28 PSI is what really got my attention.
Fuel pump electrical testing
I’m also investigating whether the fuel pump may not be receiving full voltage.
During one test with the engine running, I measured approximately 6.85 volts while trying to check the fuel-pump circuit.
I’m not yet confident enough in how that measurement was taken to say that the pump itself is definitely only receiving 6.85V. I still need to verify the measurement directly and make sure I have a known-good ground/reference point.
So I’m not calling this a confirmed low-voltage condition yet.
However, if I confirm that the pump really is receiving substantially reduced voltage, it would obviously be very interesting in light of how slowly the fuel pressure builds.
I’m currently trying to figure out the simplest/reliable way to measure actual voltage reaching the pump and also check the pump ground.
IAC
The IAC was one of my first suspects because cracking the throttle slightly keeps the engine alive when cold.
I:
- Removed and cleaned the original IAC with throttle-body cleaner.
- Installed a new IAC gasket.
- Eventually replaced the IAC completely with a brand-new IAC and gasket.
No meaningful improvement.
Interestingly, after initially cleaning the IAC and MAF, the cold-start problem actually seemed worse than it had been previously.
Before that cleaning, the truck would sometimes stay running after just a small tap of the throttle.
Afterward, I sometimes had to actually hold the throttle slightly open for a while to keep it alive.
Replacing the IAC with a new one did not fix it.
MAF
The MAF sensing wires were originally very dirty — black with a greasy-looking coating.
I cleaned them by spraying them with actual MAF sensor cleaner. I did not intentionally touch or scrub the sensing elements.
They looked clean afterward.
As a test, I later tried starting the truck with the MAF unplugged.
With the MAF disconnected, it started and immediately stalled. I could restart it and keep it running by holding the throttle slightly open.
I then shut it off, plugged the MAF back in and restarted it. At that point it was able to idle on its own, although somewhat roughly.
However, the engine had already been running for a minute or so by that point, so it was no longer a true stone-cold comparison.
ECT sensor
I suspected the Engine Coolant Temperature sensor because the problem is strongly temperature dependent.
My thought was that if the PCM incorrectly thought the engine was already warm, it might not command the appropriate cold-start fueling.
Rather than trying to accurately resistance-test the old sensor, I replaced the ECT with a new sensor.
I also cleaned the electrical connector with automotive electrical contact cleaner, blew it dry and used dielectric grease before reconnecting it.
Replacing the ECT made no noticeable difference.
Electrical connections
While working on this, I cleaned the electrical connectors for the:
- ECT
- IAC
- MAF
I used automotive electrical contact cleaner, blew the connectors out with compressed air, applied dielectric grease and reconnected everything.
No improvement.
Spark plugs
I also removed the old spark plugs.
The plugs had dark deposits on them, which seemed consistent with the other indications I’ve had that the truck may have been running rich rather than obviously lean.
The gasoline smell from the exhaust has been noticeable for months.
Fuel-pressure regulator
I pulled the vacuum hose off the fuel-pressure regulator.
The vacuum hose/regulator connection did smell like gasoline.
That initially made me suspicious of a ruptured FPR diaphragm.
However, I checked more carefully and could not find any actual liquid gasoline.
I touched both the end of the vacuum hose and the vacuum fitting on the regulator and both were dry.
So while there was a gasoline odor, I have not found actual fuel in the FPR vacuum line and therefore don’t consider the regulator diaphragm proven bad.
Where I’m at now
The thing that seems most significant to me is the relationship between the cold-start problem and what I’m actually watching happen on the fuel-pressure gauge.
On a stone-cold start:
Engine starts at only ~2–3 PSI indicated fuel pressure.
Engine immediately struggles and tries to stall.
Fuel pressure slowly climbs instead of immediately reaching normal pressure.
It takes roughly 20 seconds to reach ~28 PSI.
As this is happening, the engine is gradually becoming more capable of staying running.
That makes me wonder whether the original “cold-start problem” is actually the engine trying to run while the fuel system is taking far too long to establish adequate rail pressure.
The possibilities I’m considering now are:
- Weak/failing fuel pump
- Low voltage reaching the pump
- Excessive resistance somewhere in the pump power circuit
- Poor fuel-pump ground
- Fuel-pump check valve problem/pressure bleeding back
- Problem with the fuel-pressure regulator
- Restriction in fuel delivery
- Internal leak somewhere in the system
- Something else I’m overlooking
I’m especially interested in hearing from anyone who has worked on these early 4.0 OHV return-style systems.
Has anyone seen a 4.0 actually start with only a couple PSI at the rail and then take ~20 seconds of running to slowly build to around 28 PSI?
And if so, what caused it?
I’m particularly interested in whether anyone has seen this caused by a weak pump versus low voltage reaching an otherwise functional pump.
My next step is probably to get a trustworthy voltage measurement at the fuel pump/pump circuit and determine whether the pump is actually being supplied with proper voltage while it’s producing these low/slow pressure readings.
Fuel filter
I also replaced the fuel filter with a new one while diagnosing this problem.
Replacing the filter did not correct the cold-start stalling or the slow fuel-pressure buildup.
So the slow pressure rise I’m seeing — only a couple PSI when the engine initially starts, followed by a gradual climb to approximately 28 PSI over about 20 seconds — is occurring with a new fuel filter installed.
