97 Blazer - ignition or fuel problem?

[Kgal59]

My husband's 97 Blazer is having problems. It suddenly started running rough last weekend during the heat, then wouldn't start (had to get it towed home). Now we can only start it with starting fluid. After we start it and leave it in park, if you slowly apply the gas it will rev up fine, but if you hit the gas fast, it sputters and bogs and backfires, like it's either missing or not getting enough fuel. Also, while in park, the speedometer will move slightly as you apply the gas, even though it isn't moving. Fuel pressure is good, replaced the computer and spark plugs, tested ignition control module and fuel intake sensor, and exhaust line for any blockage. If we start it, then take off the air intake, the engine sputters and dies. Are there any sensors or other parts known to be problematic with 97 Blazers that we should check into? Anything else we should check? It has about 140k miles, it's a 4WD with auto tranny. Any suggestions are appreciated.

[mike2004tct]

Known problem for '97s.

Bad ignition switch module (wiring harness to key tumbler assy).

When truck wouldn't start, were the dash lights/gauges not working?

[Kgal59]

We took the ignition control module to Autozone, and it passed. So did the coil.

Is there a way it could be bad even if it passed the test?

[Gabe25]

Originally Posted by Kgal59

My husband's 97 Blazer is having problems. It suddenly started running rough last weekend during the heat, then wouldn't start (had to get it towed home). Now we can only start it with starting fluid. After we start it and leave it in park, if you slowly apply the gas it will rev up fine, but if you hit the gas fast, it sputters and bogs and backfires, like it's either missing or not getting enough fuel. Also, while in park, the speedometer will move slightly as you apply the gas, even though it isn't moving. Fuel pressure is good, replaced the computer and spark plugs, tested ignition control module and fuel intake sensor, and exhaust line for any blockage. If we start it, then take off the air intake, the engine sputters and dies. Are there any sensors or other parts known to be problematic with 97 Blazers that we should check into? Anything else we should check? It has about 140k miles, it's a 4WD with auto tranny. Any suggestions are appreciated.

If your ignition module tested OK, Then I would look at your Fuel Pressure. Post back your Fuel Pressure reading on Ignition on, then while engine running. The problem your incountering really sounds like your fuel pump is not delivering the right amount of pressure. Or possibly you have a plugged fuel filter. In either case. your fuel pressure reading will tell alot.

[mike2004tct]

Originally Posted by Kgal59

We took the ignition control module to Autozone, and it passed. So did the coil.

Is there a way it could be bad even if it passed the test?

I mentioned the Ignition switch harness (part of the steering column assembly) not the Ignition control module.

It's a wiring harness that has a tendancy to cause all electrical power to the engine fail intermittantly. At some point it fails on all 97s.
Do you know if it was ever replaced on yours.?

Do a search in this group, and you will see numerous threads about, some that have the same symptoms as yours.

[Rick Norwood]

Originally Posted by Kgal59

We took the ignition control module to Autozone, and it passed. So did the coil.

Is there a way it could be bad even if it passed the test?

Yes. I have had Ignition modules test good at Autozone and found them to be bad later and had to replace them. I had a 93 blazer that would die when hot, but it would start and run fine when cold then die as soon as it got hot again. The Parts stores guys will tell you that they either work or they don't and that heat don't matter. That is total BS, and I proved it. I ultimately replaced two different ignition modules in the 93 because of symptoms I described. And finally, I came to the conclusion that the testing machines at Autozone are not always accurate.

However, before you throw any more money at your truck, some good testing is in order. Did you loose any dash gauges/lights when the truck was sputtering? As Mike stated, the 97's were notorious for bad Ignition switches.

[Kgal59]

Gabe - fuel pressure was good at idle, about 60 psi. I've talked to a couple mechanics as well as my father (who used to be a mechanic), and they said that's good, they don't think it's the pump or filter.

mike2004 - sorry, I misunderstood. I'll look into that.

One mechanic said he thinks it might be the fuel pressure regulator, which is apparently under the "intake plenum" (sorry, I'm not familiar with that kind of detail on cars). Another mechanic said he will diagnose cars for free, and we don't have to have him fix it or anything, so we might just do that to see what the problem is.

[Gabe25]

Heres how you can check your fuel pressure for leaking. With the ignition switch on. You should have 61-65 lbs of pressure. Ignition switch off, your pressure should not drop below 55psi within 5 minutes. If it drops below 55psi before 5 minutes. You’ll need to check to see if your injector or Fuel regulator are leaking.