"backfire" sound under acceleration + engine dies

Ymc226

Member
I also posted in the other forum to get more opinions.

1995 NAS D90

I cleaned the throttle body, replaced the stepper motor twice and plenum intake hose (from SafariHP) and it seemed to help somewhat but what I am going to describe still happens.

After starting the truck cold, it idles fine at around 1000 rpm. Under acceleration when pressing the gas, about 5% of the time, I hear a "backfire" type sound that seems to come from the area just in front of my feet along with a sensation of a little explosion just in front of the pedals. I don't lose power and continue to drive for a while. Then unexpectedly and without any indication of a rough idle (never early in the drive but may be about 30 minutes to an hour later), the engine dies, the oil light comes on and I can usually restart the truck with a simple turn of the key initially.

This seems to repeat at a quicker interval if I keep on driving and it becomes harder to restart the engine (seems to not want to turn over as easily). The temp gauge do not indicate an issue.

When this first occurred, the idle became unstable and I could sense the engine would die, but now with what I mentioned I have done, it goes from a smooth/normal idle to just die.

Does the backfire sound give a clue to what is happening?
 

RBBailey

NAS-ROW Addict
Callsign: KF7KFZ
Do you see the backfire reported on the tach? Does it actually backfire out the tailpipe, or are you only hearing a cough in the engine area?

This has a distributor, right? And have you checked the exciter wires, the coil, the plug wires, suction hose, overall condition of the dizzy?
 

Jeff B

Well-known member
Is your intake plenum loose?

These motors are notorious for getting loose plenum bolts.
I was once looking over a friends truck and we found all his plenum bolts barely finger tight; some were very loose.


.


.
 

rocky

NAS-ROW Addict
Intriguing. At the basic level a backfire is unburnt fuel igniting at the wrong time.
Does it happen only after a cold start?
Have you checked timing?
Misfires are sometimes hard to feel when driving a V8.
Have you checked manifold, exhaust, cats for cracks, gasket failures and holes?
 

Ymc226

Member
Do you see the backfire reported on the tach? Does it actually backfire out the tailpipe, or are you only hearing a cough in the engine area?

This has a distributor, right? And have you checked the exciter wires, the coil, the plug wires, suction hose, overall condition of the dizzy?

The "backfire" is the best I can describe the sound. It isn't from the tailpipe but seems to me to come from right in front of the pedals in the engine compartment. I haven't noticed anything strange in the tach when this happens but I'll keep a closer eye on it.

I check the wires and cols; what should I look for?
 

Ymc226

Member
Is your intake plenum loose?

These motors are notorious for getting loose plenum bolts.
I was once looking over a friends truck and we found all his plenum bolts barely finger tight; some were very loose.


.


.

Thanks, I'll check the bolts.
 

Ymc226

Member
Intriguing. At the basic level a backfire is unburnt fuel igniting at the wrong time.
Does it happen only after a cold start?
Have you checked timing?
Misfires are sometimes hard to feel when driving a V8.
Have you checked manifold, exhaust, cats for cracks, gasket failures and holes?

I don't think it is a true backfire coming from the back of the truck but is the closest in describing what it sound like. The engine fail only happens 30 minutes to over an hour afterwards being driven so the engine is fully warmed up but the "backfire" sound can happen starting after 5 or so minutes from start.
 

RBBailey

NAS-ROW Addict
Callsign: KF7KFZ
The backfire you describe, if it really is going out the exhaust, could be a lot of things. But as far as the ignition side is concerned -- Look for overly dirty, burnt looking wires, look for cracks in the insulation, look for cracks in the black vacuum tube, I think there is also one or two small wires that lead to the distributor that might have issues.

Timing is another thing to check. I'd have a shop do adjustments, but I think checking should be easy. Check on YouTube.

The backfire could be brought on by this stuff. However, it could be caused by an exhaust valve issue, or as others were saying, something to do with the exhaust piping itself.

Now, as far as the car dying when at idle.... I'm going to just throw this out there as a possible, but I don't know if it actually is possible with this car. On my Series truck, I often have issues with vacuum in the fuel line. On days 80 degrees or warmer, the fuel actually boils in the line where it passes over the engine block, this vaporizes the fuel, causing a vapor lock in the line. It runs out of gas. This is probably not happening with you, but it might be something along the same lines of a fuel leak, or air leak into the system that, once the car is warmed up, actually manifests itself at low idle. You don't notice it when cooler, or when under load, but once the idle drops, it simply runs out of fuel. Just a thought.
 

rocky

NAS-ROW Addict
Time to go out on a limb. Leaky fuel injector when shut off-the extra fuel gets to the hot cats and bang.

As for the stall when warm. Its a little trickier. Seen something similar to vapor lock on a TLC. It started fine but crapped out after use. Cause was traced to a weakening fuel pump that gradually lost pressure with use.

Check the coil to. Any signs of leakage? These need their coolant, but if they lose it, they overheat. But, it takes time for them to cool off enough to allow the truck to restart. I'm putting that low on the possible causes list.
 

Ymc226

Member
The backfire you describe, if it really is going out the exhaust, could be a lot of things. But as far as the ignition side is concerned -- Look for overly dirty, burnt looking wires, look for cracks in the insulation, look for cracks in the black vacuum tube, I think there is also one or two small wires that lead to the distributor that might have issues.

Timing is another thing to check. I'd have a shop do adjustments, but I think checking should be easy. Check on YouTube.

The backfire could be brought on by this stuff. However, it could be caused by an exhaust valve issue, or as others were saying, something to do with the exhaust piping itself.

Now, as far as the car dying when at idle.... I'm going to just throw this out there as a possible, but I don't know if it actually is possible with this car. On my Series truck, I often have issues with vacuum in the fuel line. On days 80 degrees or warmer, the fuel actually boils in the line where it passes over the engine block, this vaporizes the fuel, causing a vapor lock in the line. It runs out of gas. This is probably not happening with you, but it might be something along the same lines of a fuel leak, or air leak into the system that, once the car is warmed up, actually manifests itself at low idle. You don't notice it when cooler, or when under load, but once the idle drops, it simply runs out of fuel. Just a thought.

Time to go out on a limb. Leaky fuel injector when shut off-the extra fuel gets to the hot cats and bang.

As for the stall when warm. Its a little trickier. Seen something similar to vapor lock on a TLC. It started fine but crapped out after use. Cause was traced to a weakening fuel pump that gradually lost pressure with use.

Check the coil to. Any signs of leakage? These need their coolant, but if they lose it, they overheat. But, it takes time for them to cool off enough to allow the truck to restart. I'm putting that low on the possible causes list.

Thanks to both of you. I will keep this in mind but it does make sense. Given my rudimentary mechanical skills, the next step will be to my local Land Rover specialist.
 

geatlander

Active member
I suspect that you have a bad catalyst. It is probably partially clogged and creating enough back-pressure to create a hard-starting condition. It is possible that some of the matting is still expanding a little under high heat, causing the issue to be more prevalent after the engine runs for a period of time.

http://www.autoserviceprofessional.com/article/93529/Catalytic-converter-diagnosis?Page=5

I cut mine off, hollowed them out, and refitted them. There is no emiisions check where I live, but I did the same years ago with a RRC and it still passed the emissions check in Ohio.
 
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