Blogs Car Info Our Show Deals Mechanics Files Vehicle Donation

Specific and consistant misfire

V-6 Dodge Dakota with 245K on it runs and drives great, no oil burning,leaking… but has recently developed a mis fire at idle and trouble code is saying that #4 is mis-firing. Compression check confirms low 90 psi for that cylinder. Mis-fire totally goes away while engine is under load. I think it’s a weak or cracked valve spring. I have taken very good care and it still has the original motor and tranny. Synthetic oil used since 30K -original owner.

Thanks for the report.

Seriously though. Did you want to ask something? The low compression is your problem. A leakdown test can tell you more about where the problem is. A vacuum gauge will actually give you indications of valve spring problems (though the vac gauge readings are rough indicators). Either way, something fairly major has to come apart if you want to remedy this (head work, block work or both).

Hi: Sorry for not asking a question in my post… I was wondering if it sounds like a valve spring? Usually when a valve is burnt it will continue to misfire throughout the rpm range of the motor. I would rather not tear it apart and do a rebuild- I would just install a re-man motor or sell it as is at 245K. A leak down test was done still showed the #4 cylinder coming in at 90 psi- it’s not in the lower. And no oil in the water jacket or oil burning either. But why does it smooth out under load? Very strange for a blown head gasket,burnt valve,crack head ect… to be doing that. My theory is that under load that weak cylinder’s valve seats against the head to seal it better then when it’s a more resting pressure at idle- when the problem presents itself. Have you guys seen or heard of this happening (I’m sure it has) before? Thanks for input and time.