87 4.0 won’t start

[chastings]

I'm having issues with my 87 4.0 Comanche and not sure where to start. It has spark and seems to crank relatively fast. I started with the crank sensor but not sure if I tested it right. I probed the + from my voltmeter to the red wire and the - of the meter to the white (coming  off the cps). When cranking it basically shows .8 volts (which seemed high).

It was running fine when I pulled out of the driveway but it needed power steering fluid. I turned it off, topped up the fluid, fired it back up and it immediately felt like it was running on only half the motor. I pulled it back into the driveway and it wouldn’t restart. 

Curious where else I should look. Thanks

[cruiser54]

It's AC voltage at the CPS. 

Have you visited my website and completed Tips 1 through 5 yet?

The C101 connector described in Tip 2 can cause the CPS signal to not reach the ECU. 

[chastings]

14 minutes ago, cruiser54 said:

It's AC voltage at the CPS. 

Have you visited my website and completed Tips 1 through 5 yet?

The C101 connector described in Tip 2 can cause the CPS signal to not reach the ECU. 

Thanks! I’ve actually performed 1, 2 and part of 3 so far but ran out of time. I noticed I could smell gas and there is fuel pressure at the rail as well.

 

I’ll finish up tips 3, 4, and 5 and follow up

[chastings]

Ok, so, I’ve done cruiser tips 1-5 (excluding 4). 4 was not done because the truck is not at the house and I didn’t have any torx tools with me. Additionally, I put the timing light on the truck and I do appear to have spark (so 4 may be a moot point anyways).

 

I double checked the crank sensor and it’s basically .8 ac volts

 

i double checked the sensor grounds and they’re steady at 3.9 ohms

[eaglescout526]

So are you getting any fuel from the pump?

[JustEmptyEveryPocket]

My next guess would be fuel. Put a gauge on the schrader valve and see what you get while cranking.

 

In my experience the list of things that keep a truck from firing is pretty short. I would attack it in the following order:

1. Spark - You state you have that. I would be tempted to triple check for spark at the end of a few plug wires. Pull a wire, put in a spare plug, ground it against the block and crank. Look for a bright blue spark.
2. Adequate fuel - What I am suggesting you check next. Fuel pressure should be ~30psi. I suppose it could be a faulty injector. After trying to start normally, try to start it in clear flood mode. Press the gas pedal completely to the floor while cranking. This should turn off all your injectors allowing any excess fluid to get purged. See what happens.
3. Adequate Fuel - Hillbilly style - Spray some brake clean or similar flammable liquid down the throttle body, then try cranking the truck over. If it fires and then dies we know its a fueling problem. Be extremely careful with this. Fire and explosions are not only possible by likely if done incorrectly.
4. Air - Unless the truck was launched into space I am guessing you are ok here
5. Compression/ Timing - If the truck had been running fine then up and quit (without obvious explosive detonation) I would again assume this is ok. But depending on the above, this would be my next thing to check.

There are lots of things that might keep it from running well, but the above should guarantee it fires.

[chastings]

Ok, so, I‘ve replaced the spark plugs and verified that they are firing by grounding one against the rocker cover.

 

The truck does seem to sound different than it used to (can’t describe it) when it cranks. It seems fast but gives no indication it wants to start. Also, I smell gas but the plugs seem dry when I removed them for inspection.

 

I guess I’m going to work on the ground at the dipstick to see if I can get it closer to 0 ohms (currently almost at 4.0).

 

also, should the crank sensor generate 8.0 AC volts? 

[JMO413]

Have you checked fuel pressure yet? 

[chastings]

10 minutes ago, JMO413 said:

Have you checked fuel pressure yet? 

I have not, I don’t have a tool to test it. But it seems to put out adequate fuel. I can open the schraeder valve and fuel sprays out. Additionally, there’s a strong fuel smell each time I cycle the key. After replacing the fuel filter, the first time I cycled the key there was fuel coming out from the filter outlet. I had to retighten it even more. At this point, it appears to be getting plenty of fuel but I could be wrong.
 

Any recommendations for a gauge to check fuel pressure on a 4.0? 

[JMO413]

Any automotive fuel pressure gauge will work. The injectors don't work correctly without 30 PSI. When the house from the fuel pump to the sender hose feel of mine I was getting fuel, just not enough pressure. 

[JustEmptyEveryPocket]

Most places will rent a gauge free of charge (you pay a deposit). Get that done and report back.

[cruiser54]

Or try a spritz of starting fluid....

 

 

[JimB]

You stated that it sounds different. Cranks fast. Pull the oil fill plug on valve cover. Have someone crank engine. See if rocker arms are moving. Pull plugs check for compression.

 

[chastings]

7 hours ago, JimB said:

You stated that it sounds different. Cranks fast. Pull the oil fill plug on valve cover. Have someone crank engine. See if rocker arms are moving. Pull plugs check for compression.

 

I did these yesterday, yes the rockers are moving and there is compression. At this point, guessing it sounds different (big guess) because there’s no fuel being squished in the cylinders. 
 

If working on the block ground and fuel pressure checks but still won’t start, I’ll tow it to the local Jeep mechanic. Everything seems correct but it could be something with the fuel pump or timing.

 

strange, it literally went from running perfect to running on basically half the motor and then not wanting to start at all.

[Ωhm]

Does your vehicle have a Ballast Resistor for the fuel pump circuit? 87's could be wired a couple different ways.

[chastings]

1 hour ago, Ωhm said:

Does your vehicle have a Ballast Resistor for the fuel pump circuit? 87's could be wired a couple different ways.

Nope, this is an earlier 87 and does not have the resistor 

[Ωhm]

Take a voltage reading at D1_6 during engine CRANK.

 

[JMO413]

2 hours ago, chastings said:

I did these yesterday, yes the rockers are moving and there is compression. At this point, guessing it sounds different (big guess) because there’s no fuel being squished in the cylinders. 
 

If working on the block ground and fuel pressure checks but still won’t start, I’ll tow it to the local Jeep mechanic. Everything seems correct but it could be something with the fuel pump or timing.

 

strange, it literally went from running perfect to running on basically half the motor and then not wanting to start at all.

Mine did the same thing. The line from the fuel pump to the sending unit fell off.

[cruiser54]

Starting fluid $5.

[chastings]

On 8/12/2020 at 11:19 AM, Ωhm said:

Take a voltage reading at D1_6 during engine CRANK.

 

Ok, thanks. Voltage during cranking at D1 is between 10.7-11.0 volts

 

also, this is bizarre, but I opened the butterfly to squirt starting fluid into the intake and the intake is half full of fuel (I assume). The truck won’t sneeze or fire at all. 

[Ωhm]

2 minutes ago, chastings said:

also, this is bizarre, but I opened the butterfly to squirt starting fluid into the intake and the intake is half full of fuel (I assume). The truck won’t sneeze or fire at all.

That sounds dangerous. Take caution.

[Ωhm]

9 minutes ago, chastings said:

Ok, thanks. Voltage during cranking at D1 is between 10.7-11.0 volts

Voltage shows good. D1_6 should be the same voltage at the fuel pump. Should be.

 

Quick Distributor Indexing Test:

Remove Distributor Cap. Move Crank timing mark to TDC. Rotor should either be just pulling away from Cylinder #1 or Cylinder #6. Will depend on which cylinder is on the compression stroke.

[Ωhm]

Check vacuum hose between Fuel Pressure Regulator (FPR) and intake manifold for raw fuel.

[chastings]

12 minutes ago, Ωhm said:

Check vacuum hose between Fuel Pressure Regulator (FPR) and intake manifold for raw fuel.

Haha, son of a b*@ch! It’s pouring fuel from the regulator into the intake through the vacuum line.

[chastings]

So, there’s still some gas in the intake manifold but won’t start. What else should I check? Are there any sensors that could’ve been damaged from raw fuel filling the intake?