Odd Starting Issue: '98 4.0 Disco I

RBBailey

NAS-ROW Addict
Callsign: KF7KFZ
My son's Disco has had an odd starting issue for a while where it just doesn't like to catch the first go around. It reminds me of when a vehicle is out of gas.

So I have tried to let the pump run for a few seconds before starting, but that doesn't seem to make a difference.
I've pulled all the plugs and found that none of them looked odd, but they were all gapped way too wide. That didn't make a difference.
It has been throwing misfire codes.
I checked the pressure at the fuel rail by simple seeing what happens when I depress the valve:
  • Overnight, fuel flows well.
  • After turned off for a few hours, fuel gushes.
  • While running, fuel gushes.
So I have new plugs and leads on order to see if that fixes the start and misfire issue. But before I was able to get them, the truck broke down on my son while he was in a parking lot trying to drive home. He said it first just died while in idle. Then he restarted, and tried to back out, but it died again, and would not start.

When I got there, and after confirming that it won't start, and seems like it is out of gas, I just decided to do a quick parking lot assessment: electrical connections, and nothing weird, then air, spark, fuel. The one that didn't check out was the fuel. Unlike previously, this time when I depressed the valve on the fuel rail, all I got was compressed "air". After 5-6 seconds of hissing, it sort of spits fuel.

This seems really strange to me. I don't think it's possible to have vapor lock. And their is obviously pressure in the line. So it must be picking up air someplace?

It was nearly 100 degrees out, and the engine was too hot to fool with much. So we left it for a few hours. I came back, and after giving its signature cough, it started. But at first it was obviously misfiring. Once that cleared, it drove normally for the whole way home, stop and go, and at freeway speeds. At first it did not have a check engine light on, but by halfway home it lit up.

I plan on changing the plugs and wires tomorrow or Monday, then the coil pack if that doesn't fix it. But what of this air in the fuel line? Any other thoughts?
 

rocky

NAS-ROW Addict
Being a 96 with OBD2 did you pull the codes to see which cylinder(s) is/are misfiring?
 

RBBailey

NAS-ROW Addict
Callsign: KF7KFZ
I’m kind of leaning that way too. If the fuel pump is going bad, I suppose it could trigger all sorts of other issues.

trying to remember: does this have access door inrear?
 

RBBailey

NAS-ROW Addict
Callsign: KF7KFZ
OK. If my Harbor Freight rester is to be believed, I’m at 27 psi on the fuel rail, and it only bounces a bit when revved.

It seemed to start fine today, and isn’t missing or acting odd at all.
 

Robert

Well-known member
Does it hit 37.5 when the engine is off? If not you got problems. Bad pump, big injector leak. Maybe a regulator, but never heard of that happening to a GEMS truck
 

RBBailey

NAS-ROW Addict
Callsign: KF7KFZ
When I hooked it up today, I had erroneous readings at first because the tool piping was leaking. So I don't know what the pressure was overnight. After a few tries to stop it from leaking, it idled at 27, ran at 27+/-.

Now, after running to full temps, revving, etc... and sitting for 1/2 hour, it reads 33 psi.

I've also had a few people tell me these issues sound like what they had with clogged fuel filters. I'll check if NAPA happens to have one tomorrow. Worth a try for $12 or so. Your idea about leaking injector or regulator could answer to why there was air in the system last night. I'm sure that must have been what was causing it to run badly, and die in the 100 degree heat.
 

Robert

Well-known member
Well the air wouldnt be pressurized if it was leaking down, thats what makes me think pump


That filter has got to be the most common fuel filter in the US. Jeep and GM used it on everything in the late 80s and 90s. Hit the fittings with PB plaster now. Even in rust free areas its a lotto ticket on having to repair the fuel lines or not when doing a filter

Also make damn sure the schraeder valve is closed when removing the HF gauge adapter. Ive had it stick open a few times on me
 

Robert

Well-known member
Good call. The wiring insulation by the sensor has degraded on every one Ive looked at. I pop the pins out and sleeve it with heatshrink. Typical symptoms are no start or running like crap in rain or after a car wash
 

RBBailey

NAS-ROW Addict
Callsign: KF7KFZ
Right, I'll check that. Ignition wires was my first hunch, and I've already checked the leads, and regapped the plugs, but I'm picking up a new set of both tomorrow regardless. It's a cheap enough thing to try. I was then going to go for the coil pack.

However, the fact that it acts like it is out of gas, and the oddness of the air in the line yesterday got me moving down this road. Along with what others are telling me has happened to them with clogged fuel filters.

One way or another, I'm getting the filter and ignition parts tomorrow, then will probably have to hand it over to an expert if it isn't fixed after that.
 

RBBailey

NAS-ROW Addict
Callsign: KF7KFZ
I don't have any clue how old these wires and plugs are, only that we've never touched them in two ...three? years of ownership.

The pressure in the line dropped below 30 after about 2 hours. It started fine, and ran at 27 psi. After shutting down, it went back up, but I don't think it is going to return to 35 before dropping again.

Crank position wires to the cover are OK, but the plastic surround is almost gone. I'll open the cover tomorrow when I don't have to worry about bumping the hot exhaust.
 

RBBailey

NAS-ROW Addict
Callsign: KF7KFZ
The pressure is below 20 as of this morning.

I know how this is going to make me look, but I need to know how to get the stupid fuel filter off. I have three sets of metric and standard pipe spanners of different ranges, I have three other sets of metric and standard spanners of different ranges. None of them fit either of the nuts on the line or filter. I've replaced one of these before, probably 10 years ago. So I assume I must have borrowed the tools. I just need to know what type and size I should use.
 

RBBailey

NAS-ROW Addict
Callsign: KF7KFZ
It has to be 5/8, but it doesn't quite fit. And I don't dare put any more pressure on it with an adjustable spanner.

Should the pressure not drop at all overnight? When I started the car just now, it certainly had trouble, just like being out of fuel. There must be a leak someplace, and air must be getting in.
 

RBBailey

NAS-ROW Addict
Callsign: KF7KFZ
I did find a couple of 5/8 wrenches, and bought the one that looked like it has the best quality. But it really is still too loose on the nut, resulting in it getting stripped. I it too a good bit of hammering to get it off....

What course of action should be taken? I thought I was starting with the cheap and easy step that several people told me worked for them, but I have to abandon that option.

It seems like a fueling issue. And that seems like it should quickly narrow down to the fuel pump. So is there any other test I can perform to see if it is the pump before dropping $400 on a guess?
 

pmatusov

Technical Excellence Contributor
Callsign: AK6PM
$400 for the fuel pump on a 95???
I am not advocating buying something THAT cheap, but the most I've paid for one was $70.
It takes about an hour and a half to pull fuel pump assembly out of a 95 Classic, drain and dry it out, and replace the pump motor, strainer, and wires, and reinstall it.
Matter of fact, it takes even less to do it in 100-degree weather in Yuma, AZ.

I am not also certain of the occasional no-start is caused by low fuel pressure. These trucks are quite tolerant of that.
 
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