Fuel injection/carburator question

I have a bet going on between myself and my dad. Is a '92 Cherokee sport a fuel injected engine? It's the 4.0L I6. He seems to believe that fuel injected engines do not have spark plugs. Is this true, or is he just senile? His main argument being from a Cat Tractor he used to run had glow plugs on the fuel injected engine. Do only carburated engines have spark plugs? Any help is greatly appreciated.

Some basic information for you...

ALL gasoline engines have spark plugs. They won't run without them. There is no such thing as a glow plug for a gasoline engine.

ALL Diesel engines have glow plugs. That's how they're started. Glow plugs are used to bring cylinder temperatures up until the engine reaches operating temperature. Theoretically, the glow plugs are only "ON" for the first few minutes after a cold start.

ALL Diesel engines are fuel injected. Can't do a carb on a Diesel. In fact, the Diesel does NOT compress an air-fuel mix - the air is greatly compressed and the fuel is injected at the time it needs to burn (that's how they work without an ignition system.)

Gasoline engines may be carburetted or fuel injected. Unless modified, ALL Jeep 4.0 engines have "Multi-Port Fuel Injection," with a single injector for each cylinder (total of six injectors.) There are various types of fuel injection, but they boil down to either "throttle body" (where a throttle valve/fuel injector assemble replaces the carburettor) or "port" (where there is a single injector for EACH cylinder.)

This is all VERY basic information. I could go into a lot more detail (I've been fixing automotive things for about 25 years now!) but only if you're ready...

The short form of it all is that he's right (since the Cat was a Diesel it had glow plugs) but you win (since you're talking about a gasoline engine, not a Diesel.)

Hope this helps.

5-90

That is exactly what I needed to know, plus I won the bet, so it all works out. Thank you very much. It's always nice to keep one up on the ole' man.

The last carbeurated vehicle sold in the U.S. was the 1990 Subaru Justy. There hasn't been a carbed jeep here in about 20 years.

Cool - what'd I win?

Just don't rub it in too badly - you might still need yer old man every now and then!

It's easy to remember tho - gasoline REQUIRES spark plugs, while Diesel NEVER has them.

Oh - and the 258ci inline six was, I believe, carburetted until about 1990-1991, at which time it was finally and fully replaced with the 242 inline six we all know and love...

The Volkswagen vehicle line maintained a number of carburetted vehicles into the mid-1990's - not because it worked better, but because they didn't want to waste parts that they'd already had made...

Just a few points to ponder...

5-90

5-90 said:

ALL Diesel engines have glow plugs. That's how they're started.

5-90

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Not true, not all diesels have glow plugs. Most do but not all. Some of the newer ones are using some sort of heater in the intake to heat the air on startup. There are also Diesels that have no glow plugs at all. The DT360 Navistar motor is one of them. They just rely on the heat of compressing the fuel and air to start it. In the Winter you must either have a block heater or use Eather (sp?) to get it to start. For the most part you were right but seing as I have a deisel with no glow plugs I thought I would point that out.

B-loose

Must be a new thing - haven't worked on Diesels in a bit...

I wonder if they use an Ether boost, or a propane enrichment setup for cold starts? Seems the propane setup would be easier...

5-90

5-90 said:

Must be a new thing - haven't worked on Diesels in a bit...

I wonder if they use an Ether boost, or a propane enrichment setup for cold starts? Seems the propane setup would be easier...

5-90

Click to expand...

My DT360 is an '85. No Ether boost or propane on mine, but it absolutely will not start if it is below 40* without the block heater. Four Wheeler has a '92 I think and they just squirt Ether into the intake tube to aid in cold start up.

For the life of me I cannot figure out why they did not put glow plugs in these motors. May have something to do with the fact that they would rather you warm the block when cold just to help get it cranking, I'm not sure.

B

Dvipercop said:

I have a bet going on between myself and my dad. Is a '92 Cherokee sport a fuel injected engine? It's the 4.0L I6. He seems to believe that fuel injected engines do not have spark plugs. Is this true, or is he just senile? His main argument being from a Cat Tractor he used to run had glow plugs on the fuel injected engine. Do only carburated engines have spark plugs? Any help is greatly appreciated.

Click to expand...

The answer is:
Only Gasoline engines have spark plugs regardless of fuel induction.

All Gasoline engines with either FI, EFI, MPI, or Carburetor have Spark plugs either as a separate device, or on new units, have the coil mounted to them.
Without getting to indepth, gasoline uses a low compression and a spark to ignite it. The basic reason is that spark plugs and a lower compression allow for better control over the timing and speed of the burn than increasing the compression to the point where the fuel would self ignite.

Diesel engines run on fuel oil. Fuel oil does not generally react to a spark and it has a much higher vapor temp (around 100 degrees F), so other methods are required for ignition. It was found that a high compression would provide self ignition and a reasonably contolled burn, so no ignition device is needed to start or run a diesel engine. Glow Plugs are used to improve cold weather starting, not as an igniton source.