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sputtering, mild backfire


mycarsux88
09-24-2007, 10:17 AM
my 1988 4.3 liter has an issue. i was driving fine on the highway at posted speeds for about an hour. i got off of the freeway and the car started to idle roughly and stall at idle. it also runs extremely rich and backfires/sputters at around 2000 rpm. the plugs, coil, cap,wires, and fuel injector unit have been replaced. it was suggested to me that it could be a worn cam lobe or a bad valve but im not sure. if anybody knows anything it would be greatly apprecieted

old_master
09-24-2007, 08:09 PM
Is the SES light on? Have you checked fuel pressure and the systems ability to hold fuel pressure? Possibly the fuel pressure regulator or a fuel line under the upper intake manifold is leaking. It's unlikely, but not impossible, that the camshaft or a valve are the problem.

mycarsux88
09-24-2007, 11:43 PM
the service engine light is not on oddly enough i seem to have fuel pressure, could it be a valve or cam? its only got 113000 miles

old_master
09-25-2007, 10:00 PM
Before you jump to conclussions, check the fuel pressure and post your results.

mycarsux88
09-29-2007, 07:33 PM
fuel pressure is strog i reset the timing and the ses light finally came on

old_master
09-29-2007, 08:56 PM
What is the fuel pressure and does it hold after the pump shuts off?

mycarsux88
09-30-2007, 02:51 PM
i dont know the exact fuel pressure but i do know you can see fuel coming out of the injectors while the truck is idling and if you remove one of the lines and put it in a bucket fuel sprays. would it matter the exact fuel pressure? if it does how do you measure it?

tempfixit
09-30-2007, 06:18 PM
C heck this site, it shows fuel pressure testing procedure: http://www.autozone.com/az/cds/en_us/0900823d/80/12/ad/f4/0900823d8012adf4/repairInfoPages.htm

Hope this helps

mycarsux88
10-02-2007, 08:44 AM
fuel pressure reads normal (20 psi), but the car still runs poorly it almost sounds like a dead misfire so i pulled the #1 spark plug and the electrode was burned out i am so confused:banghead:

blazes9395
10-02-2007, 11:44 AM
Is it running rich? What does the spark plug look like, is there deposits from a rich running engine, does it have oil deposits, etc. If its running rich like you mentioned earlier, then you'll have to find out whats causing a rich condition. It could be a bad O2 sensor, it could be many things at this point. A bad ECM can cause all sorts of problems too. Your best bet is to get a scanner on there and see what its doing. Thats really the only way at this point. Anything other than that, and your just wasting money throwing new parts at it.

93gmcjimmy
10-02-2007, 12:29 PM
if your fuel pressure is at 20 that seems too low. before you start the engine hook up a fuel pressure guage. Then turn the engine to "on" do not start the engine. when you hear the fuel pump prime up check the fuel pressure at the intake. It should hold about 55 psi. If it starts to drop then you've got a leak. or if it never reaches 55 you've got a leak. Not all that uncommon on blazers. I had to change my regulator, lines, and injectors. they were all bad.

MT-2500
10-02-2007, 01:07 PM
if your fuel pressure is at 20 that seems too low. before you start the engine hook up a fuel pressure guage. Then turn the engine to "on" do not start the engine. when you hear the fuel pump prime up check the fuel pressure at the intake. It should hold about 55 psi. If it starts to drop then you've got a leak. or if it never reaches 55 you've got a leak. Not all that uncommon on blazers. I had to change my regulator, lines, and injectors. they were all bad.

20 lbs of fuel pressure is to high.
Fuel Pressure specs for a 88 4.3 is 9-13 lbs.

20 lbs could cause it to run rich.
MT

93gmcjimmy
10-02-2007, 02:01 PM
Your right my bad MT, that's a mechanical fuel pump isn't it? Stupid me. :banghead:

MT-2500
10-02-2007, 02:12 PM
Your right my bad MT, that's a mechanical fuel pump isn't it? Stupid me. :banghead:

It is electric in tank pump but just low pressure TBI injection.
MT

mycarsux88
10-18-2007, 01:41 AM
ok the ses light went off and now im lost again what to do?:banghead:

MT-2500
10-18-2007, 09:19 AM
Where are you at now?
Does it start and run?
Have you got spark to more than one plug?
Have you got fuel pressure and how much?
Jumper pin A and B on diagnostic connector and
Check for stored codes in computer.
Post back codes.

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