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Looking for a little help....

THISISWEIRD

THISISWEIRD

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This morning I got up to go hunting and the blazer started up fine. I pulled over to get gas and when I went to crank it up, it wouldn't start. I can't hear the fuel pump prime when I turn on the ignition. I try to start it maybe 10 times. No dice.

I didn't have time to screw with it so I called a friend to tow it to the shop.

I go to the shop and they are just starting to work on it. I tell them what's going on and they use starting fluid to see if it will fire. Sure enough it does, only it continues to run. Turn it off, crank it again, and it starts right back up. Each time they turn the key, I can now hear the fuel pump prime.

So, it's running now, but I know it's just a matter of time before it does this again. What's up here?

Some background if needed.....
It's been running just a bit weird at idle....like it's missing from time to time. It was doing a jerking under load (say going uphill in OD at about 1000-1500 RPM) but a change of plugs and wires corrected that problem.
 
Hows your fuel filter? Fair number of people have had issues with TBI that bad filters have fixed.

Starting fluid not really telling you much unfortunately, since your problem is intermittent, could have been a coincidence that you had spark at the time.

Next time it happens you need to check for fuel and spark. No spark=no fuel.

Fuel pump should work regardless of the fuel pump relay, since you have an oil pressure switch, however that takes about 4-5PSI oil pressure to close, so cranking tends to take a little longer.

You can force the pump to operate by putting 12V battery to the wire dangling off the relay connector.
 
dyeager535 said:
No spark=no fuel.

Fuel pump should work regardless of the fuel pump relay, since you have an oil pressure switch, however that takes about 4-5PSI oil pressure to close, so cranking tends to take a little longer.
Click to expand...

Thanks. I'll try the filter.
Few questions: 1. No Spark=No fuel. Why is that?
2. What does the oil pressure switch do with the relay?
A while back it took forever to start, but after cranking it for 20-30 seconds it fired up. Is this because the oil pressure did something? Does this help witht the diagnosis?
 
No Spark = No fuel (I think he is saying that if you have no power to fuel pump you will get no fuel)

Might check wire connections to fuel pump also.

I'm a TBI Noob so I will shut up now:o
 
The no spark=no fuel is because the module in the distributor is what also sends a signal for the fuel pump. So if the module goes bad you also will not get the signal to the fuel pump.
 
I've been doing some reading (amazing how that works)....4X4, I don't think that's quite right.

Looks like the fuel pump relay and the oil pressure switch are redundant systems to provide power to the fuel pump. So if the relay goes bad, the oil pressure switch will continue to run the fuel pump. It's unlikely that both of these are bad and that one is intermittingly (sp?) running.

Next time it happens I will check for spark and fuel. If no spark, maybe it's an ignition module or something related, like coil.

Any other ideas?
 
Doubt is is your coil. Possibly could be the Magnetic pick coil inside the distributor. or Bad Module as said eariler. Both will cut fuel if they go bad.
If the FP relay goes out you have to crank the starter a while to get it to start. Fuel pump wont prime if relay goes out. But it will eventually start after the oil pressure switch sees pressure.
Have you checked the fuel PSI? May have a bad pump.
 
Sounds like the choke is sticking on your carb. Also check the airfilter.
 
Quote:
Originally Posted by 1980
Sounds like the choke is sticking on your carb. Also check the airfilter.

Funny....

How do I check pressure? A gauge goes where?
Click to expand...

?????:confused:,,,Well, take out the aircleaner. Then hold the choke open & try to start. No gauges needed and the pressure is released with what we call a "fart"
 
1980 said:
?????:confused:,,,Well, take out the aircleaner. Then hold the choke open & try to start. No gauges needed and the pressure is released with what we call a "fart"
Click to expand...

It's Fuel Injection...No carb.

Checking pressure was a question for Thunder.
 
You can check fuel pressure with a guage that takes temporary place of your fuel filter.
 
Mabe this is a question for the lounge butt...........What is the normal PSI for a "Fart"?

As for checking the fuel pressure. As 4x4High said the guage goes on where the filter is. It screws in line with the filter. Check the pressure both at prime and with the truck running. Normal PSI is 9-12. Less than that and your pump is bad. It should also hold steady when running and not go up and down. Did The shop where you took your truck check the pressure? They should have. It is part of normal diagonstic procedure for TBI fuel problems.
 
Don't have time to read all the replies, so I appologize if I'm being redundant here. I have been having problems with mine for the last week. Turns over just fine, but won't fire. Tried starter fluid the other morning, and it fired up. This am, I noticed that the pedal was returning slow...like molasses slow. So, I held the pedal down rahter than making quick jabs to prime the carb. After about three tries, it fired. My cable seems to be having trouble when the temperature drops (was about 10* last night). Just something to consider.
 
Thunder, 4x4, all...Thanks.

Anyone know where I can buy a fuel pressure gauge to test this? Do I just make one with a pressure gauge, a t-fitting, and some rubber hose? Of course, this would only be a quick test.
 
Last edited:
THISISWEIRD said:
I've been doing some reading (amazing how that works)....4X4, I don't think that's quite right.

Looks like the fuel pump relay and the oil pressure switch are redundant systems to provide power to the fuel pump. So if the relay goes bad, the oil pressure switch will continue to run the fuel pump. It's unlikely that both of these are bad and that one is intermittingly (sp?) running.
Click to expand...

He's right, but there is more to it as you suspect.

The relay gets bypassed if the oil pressure switch is working right.

However, with no spark signal to the ECM, the ECM will not pulse the injectors, so you'll get no fuel. :)
 
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