So I've had a '97 Ranger about 3 months and I've been going round and round with a strange misfire. When the engine is fully hot at idle everything is normal,no misfire,vacuum steady at 20 hg/in. But when I rev it a few times to 2000 RPM or above then quickly take my foot off accelerator pedal and let it return to idle it starts misfiring BADLY and the vacuum gauge goes nuts, bouncing between 10 and 16 hg/in. But then EXACTLY 48 seconds later the misfire is completely gone and vacuum gauge is back to a steady 20 hg/in.( It's almost like Swiss timing !) What in the world is happening during that 48 seconds to cause the misfire to resolve? New plugs,wires and 2 new coils off ebay. They're cheap ones but are performing "fair".(I check them with my timing light). The 4 plugs on intake side are always clean,plugs on exhaust side usually look "kinda bad" but not really oil fouled.I've had the valve cover off a couple of times and everything seems to be functioning normally.Springs are a little weak but not bad enough you can mash them down with fingers. No collapsed lifters best I can tell. I have a couple of suspicions whats happening but I'd like to hear what you all think before I speak them.145k,2.3 four cylinder engine.TIA.
Misfire resolves in 48 seconds?
- Thread starter tomkat22
- Start date
Do a smoke test. Sounds like you may have a vacuum leak somewhere.
Sounds to me like you need a complete set of intake manifold gaskets.
I would have said a valve sticking in a guide but the 48 second thing like clockwork is strange. I wouldn't expect a mechanical issue to be that predictable. The vacuum gauge is pointing you in the right direction.
While at idle put your hand on the egr tube. If it fees hot to the touch then you have a bad valve or stick control solenoid. Also check to see if the tube is hot when it is running poorly. If it is, and at idle, that is your issue.
While at idle put your hand on the egr tube. If it fees hot to the touch then you have a bad valve or stick control solenoid. Also check to see if the tube is hot when it is running poorly. If it is, and at idle, that is your issue.
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What's weirder is I can slowly increase RPM's from 900 to 2000,then slowly bring RPM back to 900 and the misfire wont appear.Its only when I rev quickly or snap throttle the misfire comes back. Fuel trim numbers slowly return to normal after it sets at idle for awhile. I've had a P0171 code set a couple of times but I can avoid that by manipulating the RPMs.No misfire code ever.Fuel pressure stays around 40 psi.
Broken valves spring.
Originally Posted by tomkat22
What's weirder is I can slowly increase RPM's from 900 to 2000,then slowly bring RPM back to 900 and the misfire wont appear.Its only when I rev quickly or snap throttle the misfire comes back. Fuel trim numbers slowly return to normal after it sets at idle for awhile. I've had a P0171 code set a couple of times but I can avoid that by manipulating the RPMs.No misfire code ever.Fuel pressure stays around 40 psi.
P0171 is a lean code, consistent with your low vacuum readings.
The precise timing makes me suspect a computer-controlled component.
I'd start by trying a new IAC valve, to see if it makes any difference.
What's weirder is I can slowly increase RPM's from 900 to 2000,then slowly bring RPM back to 900 and the misfire wont appear.Its only when I rev quickly or snap throttle the misfire comes back. Fuel trim numbers slowly return to normal after it sets at idle for awhile. I've had a P0171 code set a couple of times but I can avoid that by manipulating the RPMs.No misfire code ever.Fuel pressure stays around 40 psi.
P0171 is a lean code, consistent with your low vacuum readings.
The precise timing makes me suspect a computer-controlled component.
I'd start by trying a new IAC valve, to see if it makes any difference.
sticky IAC or EGR component? An exact time suggests it's linked with a normal ECU program to me. MAF noise?
No broke valve spring,I inspected them closely.Weak maybe,none broke. The reason I don't think it is the IAC is because when I pull up to a red light at 900 RPM the misfire is there,then 48 seconds later I'm still at 900 RPM but misfire is gone. It seems to work okay other times as well,start up,etc.
AZjeff
$50 Site Donor 2023
Sounds like a clinebarger question.
I had the I had to the same issue I my 1998 4 ltr l ,turns out it was the gasket underneath the intake manifold, it looks like it's a fibrous one but it turns out that the original ones the o rings that are there are two compressed to seal correctly, the replacement is much thicker o rings and problems solved in my case, take off the intake manifold the plastic Parts and it'll be underneath the gas manifold but on top of the fuel injector spacer, etcetera I had it done at the dealersshop your the problem should be taken care of.
I think the parts come in a kit.
TOMB
I think the parts come in a kit.
TOMB
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I had the I had to the same issue I my 1998 ,turns out it was the gasket underneath the intake manifold, it looks like it's a fibrous one but it turns out that the original ones the o rings that are there two compressed to seal correctly, the replacement is much thicker and it's all the problem, take off the intake manifold the plastic Parts and it'll be underneath the gas manifold but on top of the fuel injector spacer, etcetera I had it done at the dealersshop your the problem should be taken care of.
I think the parts come in a kit.
TOMB
I think the parts come in a kit.
TOMB
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I take it that the truck drives OK when you're on the gas. The only problem is misfiring at idle?
Others pointed you toward the EGR system, that is definitely something to investigate. The EGR valve is not supposed to be open at idle, if it does there will be severe misfiring or even stalling, and loss of vacuum. Disconnect the vacuum hose to the EGR valve so it won't open at all, then test.
A lot of idle problems also result from the throttle position sensor not accurately telling the PCM that the throttle plate is in the idle position. Test with a voltmeter or live data on a scan tool.
Others pointed you toward the EGR system, that is definitely something to investigate. The EGR valve is not supposed to be open at idle, if it does there will be severe misfiring or even stalling, and loss of vacuum. Disconnect the vacuum hose to the EGR valve so it won't open at all, then test.
A lot of idle problems also result from the throttle position sensor not accurately telling the PCM that the throttle plate is in the idle position. Test with a voltmeter or live data on a scan tool.
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Originally Posted by mk378
I take it that the truck drives OK when you're on the gas. The only problem is misfiring at idle?
Others pointed you toward the EGR system, that is definitely something to investigate. The EGR valve is not supposed to be open at idle, if it does there will be severe misfiring or even stalling, and loss of vacuum. Disconnect the vacuum hose to the EGR valve so it won't open at all, then test.
A lot of idle problems also result from the throttle position sensor not accurately telling the PCM that the throttle plate is in the idle position. Test with a voltmeter or live data on a scan tool.
Once the misfire starts it will only completely go away by letting the engine idle for about 48 seconds. Its the most noticeable when engine is under load,like when you upshift to the next gear "sooner" than you should. But all the while vacuum readings are fairly normal. I disconnected the vacuum hose to the EGR,it seems to be working fine.I also sprayed starting fluid and propane anywhere I suspected a vacuum leak might be.Something is changing and moving in/on the engine during that 48 seconds to cause the misfire to go away at idle,I just don't know what it could be. I've heard it mentioned lifters can overfill or pump up with oil then bleed out too slow(or fast?)causing the valve to not close properly,thereby creating a vacuum loss. That combined with a weak valve spring and worn rings might explain the 48 second deal. Kind of a wild theory out of left field but I'm getting desperate here.LOL.
I take it that the truck drives OK when you're on the gas. The only problem is misfiring at idle?
Others pointed you toward the EGR system, that is definitely something to investigate. The EGR valve is not supposed to be open at idle, if it does there will be severe misfiring or even stalling, and loss of vacuum. Disconnect the vacuum hose to the EGR valve so it won't open at all, then test.
A lot of idle problems also result from the throttle position sensor not accurately telling the PCM that the throttle plate is in the idle position. Test with a voltmeter or live data on a scan tool.
Once the misfire starts it will only completely go away by letting the engine idle for about 48 seconds. Its the most noticeable when engine is under load,like when you upshift to the next gear "sooner" than you should. But all the while vacuum readings are fairly normal. I disconnected the vacuum hose to the EGR,it seems to be working fine.I also sprayed starting fluid and propane anywhere I suspected a vacuum leak might be.Something is changing and moving in/on the engine during that 48 seconds to cause the misfire to go away at idle,I just don't know what it could be. I've heard it mentioned lifters can overfill or pump up with oil then bleed out too slow(or fast?)causing the valve to not close properly,thereby creating a vacuum loss. That combined with a weak valve spring and worn rings might explain the 48 second deal. Kind of a wild theory out of left field but I'm getting desperate here.LOL.
Originally Posted by mattd
Does the egr tube feel hot while th engine is at idle??
Not that I've noticed. I've had the EGR off,sucked on it,let off and it popped closed like it's suppose to.I also replaced the DPFE sensor,no change. I have to fabricate a valve spring compressor,the 2 I tried so far didn't quite fit. I want to take a better look at the lifters and valve springs. I feel like when I find what's causing the intermittent vacuum drop the misfire will go away, I don't think its ignition related.
Does the egr tube feel hot while th engine is at idle??
Not that I've noticed. I've had the EGR off,sucked on it,let off and it popped closed like it's suppose to.I also replaced the DPFE sensor,no change. I have to fabricate a valve spring compressor,the 2 I tried so far didn't quite fit. I want to take a better look at the lifters and valve springs. I feel like when I find what's causing the intermittent vacuum drop the misfire will go away, I don't think its ignition related.
