HSO Automotive Puzzler

[Jeremy airjer W]

This is a 94 jeep wrangler with a 2.5 liter inline 4 cylinder and a manual transmission.

The customer installed a 2.5 motor out of a 1990 jeep. Just the long block was used as the 1990 was carburetor and the 1994 is fuel injected. The distributor is out of the 1994 and installed correctly (ignition timing is not adjustable). The original intake and exhaust manifolds where reused.

Here's the problem. The engine cranks over but won't start. There is plenty of spark but instead of one pulse of spark there is several pulses of spark when checked at the wires. The coil is rapidly firing spark with the engine cranking. The vehicle is flooding and will run and idle with the injectors unplugged and an external fuel source used. As soon as the injectors are plugged in it won't start. All the sensors are fine. Fuel pressure is right on and not bleeding off. The injectors are all fine.

It took me about an hour to get it in the shop, get the charger hooked up, check for spark and fuel, make sure the distributor was aligned, and finally confirmed when I called the customer to ask 2 questions and he sent me 3 pictures from the old engine.

The fix took about 2.5 hours and it only needed one part.

So what is it?

[pureinsanity]

rusted distributor cap terminal and wire?

[pureinsanity]

Or Replaced the TPS?

[Jeremy airjer W]

There is nothing wrong with the ignition system and all the sensors are good. The PCM is good as well. All the wireing is also o.k.

Remember it will run just fine with the injectors unplugged and we know its flooding with the injectors plugged in. The injector connectors are on the correct injectors and the firing order is correct as well as the timing. We also know that the spark is not one solid spark but a series of rapidly firing spark pulses, a big clue!

[Black_Bay]

I may be missing something but you said the engine cranks but won't start and then you say it idles. Did you mean it didn't start until you put on the external fuel source?

[pureinsanity]

hmmmmm. im starting to get confused. EVERY sensor is fine?

[pureinsanity]

I may be missing something but you said the engine cranks but won't start and then you say it idles. Did you mean it didn't start until you put on the external fuel source?

When the fuel injectors are unplugged the motor runs, when they are plugged back in it doesn't run and just floods

[pureinsanity]

Dirty Injectors!

[Macgyver55]

I havent worked on one of those in a long time. Where is the crank sensor located, in the bellhousing?

It sounds like its triggering too often. Did he use the old style flex plate?

Do we get to see the pictures too?

[muddpuppy]

With the use of an external fuel source. I would say fuel pump, but you state the the pressure is fine. Not high, low or disipating.

You say the big hint is in the rapid spark but all components test out fine.

Seeing that the jeep idles but does not run and floods with the injectors.

2.5hr fix

after

2?'s and 3 pictures

Something to due with a differance in the timming between the carb and injector setup timing gear size differance?

I normally am far from close but it is fun trying thx airjer

[pureinsanity]

I havent worked on one of those in a long time. Where is the crank sensor located, in the bellhousing?

It sounds like its triggering too often. Did he use the old style flex plate?

Do we get to see the pictures too?

as stated all sensors are fine. That's what I thought too but than i remembered he said all the sensors were fine.

[pureinsanity]

With the use of an external fuel source. I would say fuel pump, but you state the the pressure is fine. Not high, low or disipating.

I am sure the fuel injectors are getting that same external fuel.

[Macgyver55]

I'm not saying the sensor is bad, rather the triggering mechanism. (Flex plate in this case)

[Scott K]

I'm not saying the sensor is bad, rather the triggering mechanism. (Flex plate in this case)

+1

[theoilman]

+2 , must be what the crank sensor is triggering on.

[Jeremy airjer W]

Mac, 4, and the oil man are on track.

The 1990 was carburated but still used a crank sensor. The crank sensor is mounted to the transmission. It uses the exciter ring found on the flywheel to create its signal. THe only think the customer did not transfer was the flywheel.

After doing a little research on the web I found out that the fly wheel for an 87-90 was different than the flywheel for a 91-00. The major difference was the exciter ring. The 1990 used a toothed exciter ring ans the 91 used a ring with divets. The crank sensor was seeing roughly 4 times the divits in the toothed exciter ring and was triggering spark and fuel 4 times as much as needed. If I had live data while cranking I am betting cranking RPM was four times as much also.

The two questions I asked where, what engine is the distributor out of and what egine is the flywheel out of. The three pictures where pictures of the old flywheel still attached to the old engine.

The customer opted to go with a new flywheel and the problem was solved. Had he replaced the motor with a 1991 he would have saved himself a lot of money and time.

The flywheel on the right is the 1990 the one on the left is the 1991 and newer.

[Tom7227]

How much money and how much time? What is the lesson that could be learned?

[Jeremy airjer W]

There was the tow, diagnostic time, and labor to pull the transmission, and the cost of the part. Tee lesson learned is anytime you replace an engine with a used engine always check to make sure you transfer all the parts needed. Especially with such a large space between years. all of the used engine we get from various suppliers come without the flywheel or ring gear. One reason is they replace the seals before they send them to us and I think another is to avoid the possibility of the above happening.

[pureinsanity]

This was a neat thread! thanks for posting this riddle Do it again sometime!

[muddpuppy]

Cool... I was almost close........Thanks agian it's fun learning

[MNice]

I love these teasers.... as long as they are not about my vehicle

[Jeremy airjer W]

This was a neat thread! thanks for posting this riddle Do it again sometime!

Here's a few for you that I have done in the past

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