My jeep starts like a diesel

I have had my Jeep for nearly 8 years (97 XJ 4.0L auto 4x4) recently I have noticed when it starts up I feel like its a diesel engine starting up. My buddy has a 06 Ram Diesel and it has quite a torquey shake to it which you would expect from that truck. But my Jeep lately has been starting like that. The only other way I could put it is it is starting rather violently. Any ideas on what would cause this? I checked the motor mounts to see if maybe they were bad and it might be flopping around but they looked fine no dry rot at all.

Another thing worth noting. My factory alternator finally dies on me last week and I put a new one in. Since then I have noticed a couple of times that the jeep bogs way down after I put it in park after driving for a while. And I noticed it bogged down some when turning into my buddy's neighborhood the other day. Not sure if that is connected with the odd diesel-like start up.

"Looking OK" and actually being OK are not always the same thing.

A failed fuel line check valve will allow the fuel rail to drain. Leaky fuel injectors will leak excessive amount of fuel into the cylinders. Either problem (or both together) would cause rough idling at start-up until fuel pressure builds or the excess fuel clears out.

Can we assume that all your tune-up parts are all fresh within the last 30,000 miles ?

Clean the Idle Air Controller (IAC) and use some injector cleaner if you have idle issues.

Tim_MN said:

"Looking OK" and actually being OK are not always the same thing.

A failed fuel line check valve will allow the fuel rail to drain. Leaky fuel injectors will leak excessive amount of fuel into the cylinders. Either problem (or both together) would cause rough idling at start-up until fuel pressure builds or the excess fuel clears out.

Can we assume that all your tune-up parts are all fresh within the last 30,000 miles ?

Clean the Idle Air Controller (IAC) and use some injector cleaner if you have idle issues.

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I have seen and replaced bad motor mounts that have were dry rotten with the rubber basically having completely disintegrated around where the bolt goes through the mount. My mounts look absolutely nothing like that all the rubber is still there. That is why I think they are fine since I can't see how they would be bad otherwise. Where is the fuel line check valve and how can I test it? IAC was recently replaced and only a few months old. The plug wires cap and rotor were also replaced just a couple of months ago and have maybe 5,000 miles on them. Plugs might have close to 30,000 miles on them but I checked them when changing out the wire and they looked fine and the gaps were to spec so I left them in. I replaced the TPS once years ago but since they tend to go bad pretty often on these jeeps I was thinking maybe it was getting worn out again. I have never replaced the map sensor before and the Jeep has over 194,000 miles on it so I didn't know if maybe it could give problems such as these.

Crawl under there and inspect the engine mount bracket to block bolts--they work loose and fall out and/or shear off in the block. Next, when was the last time you replaced the engine mounts themselves? You have owned it 8 years, some of the cheaper replacements don't last even two years.

Ok--what is your static battery voltage measured between the terminals? When you start the engine and measure the voltage between the terminals what do you get?

Did all this start before or after the alternator you replaced?