1996 S10 Blazer LT 4wd automatic 4.3 182,000 miles.

It has been progressivly getting hard to start. It started months ago by not starting on the first crank. But it would start on the 2nd crank. Then it would be ok for a while. This slowly progressed to recently where it might start right up on the first crank or it may take up to a dozen or so cranks. Recently the norm was 3-5 cranks. After it was driven it usually started on the first crank. But if it sat overnight or longer is usually when the problem shows up. It always runs good with no drivability problems. It will throw an P1441 or PO446 code. I clear the code and it will not come back for a week or more of driving so I don't think this is the problem.

If it does not start right up I learned it does no good to keep cranking. If it doen not start right up I stop cranking for a few seconds and then try again. It has always eventually started until tonight. I did not have my fuel pressure gage with me but it did have fuel pressure at the test port and it has spark at the coil wire. I will go back & check fuel pressure tomorrow.

When it acts up it either does not fire at all or it will fire and not start. The next crank it may fire and run for a fraction of a second. It would keep doing this and run slightly longer each time and eventually start.

Recent items replaced, spark plugs, distributor cap & rotor, crank position sensor, map sensor & fuel filter. Fuel pump was replaced at 140,000 miles.
Fuel pressure runs 53-55 psi before and after starting. The manual says 58 psi but I have checked another Blazer and a Jimmy and they only run about 55-56 psi.

I need help in deciding what to do. Thanks.

 

for your blazer to start properly you need 60psi pump pressure

 

The factory manual says 58 psi. However I have checked another Blazer and Jimmy and they do not have 58 psi either. Both of those start fine. (Possibly my guage reads low even though it is new?)

I put the guage on this morning but the fitting on the guage is leaking so will get that fixed and test again.

If the pressure is low how do you tell if it is a pump problem or a regulator problem? I don't think the regulator is adjustable. Where is the regulator?

 

If you will read and follow the steps as outlined in this thread it will help you determine the source of any fuel delivery problems for your truck.

 

Thanks for the link to that thread. Good stuff.

I checked the fuel pressure tonight and it was 33 psi. Then it leaked down 4 psi in 12 minutes. The thread said it is a problem if it leaked more than 5 psi in 10 minutes. So it looks like the leak down is ok.

I followed the diagnosis as best as I could but I do not have access to a scan tool or the fuel pipe shut off adapter.

It seems to me that the problem is either the regulator or the pump. The pump was replaced 40,000 miles ago. It ran fine before. The only problem was hard starting.

The regulator is the cheapest but it looks like a pain to get to. How do you deal with the hard fuel lines when you lift the top section of the intake manifold. Are there any tricks to getting to the regulator?

Do you guys think it is more likely to be the regulator or the pump? Lacking the scan tool & shut off adapter is there anything else I can test or try?

Thanks for all the help.

 

[QUOTE]you need 60 psi..i would say you have a fuel pump problem

 

[quote=reelbroke2;243339]The GM manual says 58 psi but never the less it needs more pressure. In following the trouble shooting chart low pressure can either be the regulator or the pump. Without the fuel pipe shut off adapters I cannot check to see if it needs a regulator or a pump.

The low pressure can be caused by a week pump which is understandable. But if the regulator is reducing the pressure too much the pump might be ok. I thought some of you experts might have experience with this. Such as:
1. Regulators rarely go bad causing low pressure.
2. If they do cause low pressure they don't drop the pressure as low as 33 psi.

Without the shut off adapter how about this?? Take the outlet line off the fuel filter and connect a hose from the filter to the pressure guage. Turn the pump on and if the pressure is low the pump is bad and if the pressure is 60 psi or over the regulator is bad.

 

Anyone?

 

You can always disconnect the fuel line before the fuel filter and test the pumps output from there. If it is under 60, or even 58 if you wish to to use the official manual specs then the pump is suspect.

If the pressure is good at this point then I would look more towards the regulator.

However, if your pressure is low when checked at the point before the fuel filter, do not immediately jump to the conclusion of a bad pump just yet.

First check to be sure that your pump is getting a solid and consistent +12v
Low voltage to the fuel pump could cause low or inconsistent output.

There is a link to another thread or three dealing with a low or inconsistent voltage issue and possible causes and solutions for it that I will happily dig up for you if this is the case for your truck.


On a side note,

You have changed the fuel filter by this point I would hope.

By that I mean changed it yourself or at least verified for yourself visually that the one that a mechanic/lube shop said had been replaced was in fact new.
I have seen way to many times a shop not being able to easily remove the old filter on these trucks and simply proclaim that it has been replaced and leaving the original. I can think of a dozen times this has happened from as many shops right off the top of my head. A clogged fuel filter could just as easily cause your problem as anything stated above.

FYI, dropping the spare tire from under the truck usually gives fairly decent access to the pump wiring harness and all the fuel lines for the majority of model years.

 

awe341---Thanks for the reply. I checked the pressure at the inlet line to the fuel filter. It was 45 psi. I replaced the fuel filter 2,000 miles ago and it is ok. So I must have a voltage pronlem at the pump or a week pump.

I did a search and only found that you should have equal or near battery voltage at the pump when cranking. It did not say which of the 3 wires is + and it did not say if you simply test for voltage at the connector or if you check voltage with the connector plugged into the pump.

I am going out now and see which wire is + and see what voltage I get at the connector.

The pump has 40,000 miles on it and the connector still looks good as I put di-electric grease on it when I put the pump in.

If you can find the voltage threads that would be great!