Hello all,

I have been lurking through the forums to try and find a solution as to why my father's truck will not start and am at the point where I would appreciate some knowledgeable opinions.

The battery, cap & rotor, spark plugs & wires, throttle body (remaned) and fuel pump are just over a 1 year old. Everything but the battery and fuel pump were purchased from RockAuto and installed by my father's mechanic. Truck ran with no noticeable issues.

I replaced the entire ac system about 9 months ago. Vacuumed the lines and charged the system to proper spec but the ac wouldn't blow cold. I had a flight to catch so I told him I would revisit the ac issue when I am back in the country in two week. My dad brought it to his mechanic who did something to ac related vacuum lines and now the ac works until you accelerate and the ac is directed towards your feet.

About a month later the truck would start backfiring and severely lose power. At first it was while the ac was on then it just always happened. It got to the point that the truck would almost stall when coming to a stop. A solution was throwing it into neutral while coasting or at a complete stop.

About 2-3 weeks ago my father calls me telling me the truck died as he was pulling into his destination. It would crank but would not start. We had it towed to my job and I started it but it would stall in a few seconds. I left it alone for some time and it fired up and I was able to drive it.

The next day it kept dying and I realized that the check engine light never illuminates so I swapped the bulb with one that I knew works. Cycling the key on and off I was able to pull the following codes:

11 - Crank Sensor
12 - Battery Disconnected
37 - Torque Converter or Park/Neutral Switch
41 - Alternator
51 - Running Lean
55 - End of codes

After pulling the codes the truck refused to start.

What I have done so far:
Changed the fuel filter mainly because it should have been changed
New PCV Valve and grommet
New Ignition coil
New Park/neutral safety switch

I know the battery is not the issue because the truck cranks with full force. I also used jump leads as well.

I tried starting the truck in neutral as well as jiggling the shifter but still no fire.

I swapped all 3 relays just in case 2 happened to go bad at the same time. Still no fire. (AC, Auto shutdown, and Starter)
Note: truck does not have abs nor does it have the female spades to accept a fuel pump relay.

I have a new crank sensor but haven't noticed the location on the bell housing. Supposedly on the passenger side of what I have read but I just don't see it.

When cranking, I never smell any fuel near the throttle body but don't have a fuel pressure test kit.

Sorry for the long post but I would rather try and be as descriptive as possible. I appreciate any insight.

 

Bad crank sensor, you won't smell much fuel because the ECU won't turn on the ASD.

But a 1991 doesn't have a crank sensor back there; it's using the pickup in the distributor.

I'd first run the wiring down from the distributor to the ECU; after that, I'd consider the pickup in the distributor.

Also, you need - not ought to have, not should have, but NEED - the 1991 Factory Service Manual. that 1991 is a LA 318/5.2, not a Magnum, so the 95/96 books here will do you just about nothing for the motor.

RwP

 

Hello Ralph,

Thank you for all your input. I will just go ahead an order the distributor pickup from rockauto since I cannot very the age.

I did notice that the wire harness on the crank sensor was exactly the same as the distributor pickup.

As far as running the wires down, do you mean for me to trace the wires ensure continuity?

Also, is the FSM the same for the 5.2l as it is for a 3.9l?

Thank you again!

 

Yes, trace the wires to make sure it's not something dumb like a connector popped open.

And yes, same factory service manual.

RwP

 

I cannot find it in a search but I recall seeing something on here several years ago about a common failure in early 1st gens of some vacuum valve in the engine bay on the firewall that hobbles the HVAC directional control of vents.

 

After changing the coil pick up the truck fired right up and kept stumbling. I put a new cap, rotor, spark plugs, and wires and was able to keep it running at idle with barely any stumbling. It idles better when the idle air control valve is disconnected. It failed to start again after sitting over the weekend so I swapped around all the relays and found out that one completely went bad. The bad relay is now sitting in the a/c clutch slot.

Driving it becomes it's own debacle because of massive backfire and almost complete loss of power. A fuel pressure gauge was installed by a buddy it almost always displayed 15 psi. We searched for a potential vacuum leak spraying brake parts cleaner but the motors idle never surged.

We used a timing light and noted that the engine timing was advanced by 16 degrees so we turned the distributor to as close to what the sticker under the hood recommended during idle (I believe it was +7 degrees). The motor would still idle smoothly but misfire and lose practically all power when driving.

The following are the codes that were pulled from the truck using the key method:
12 - Direct battery input to PCM was disconnected within the last 50 key-on cycles (normal)
24 - Throttle Position sensor out of range
14 - MAP sensor voltage too low
33 - A/C clutch relay circuit
42 - Fuel pump relay control ckt, Auto shutdown relay control ckt, No ASD relay output voltage at PCM, Fuel level sending unit volts out of range, Fuel level unit No change over miles
11 - Timing belt skipped 1 tooth or more from initial learned value, Intermittent loss of either camshaft or crankshaft position sensor, No crank reference signal detected during engine cranking
41 - Generator field not switching properly
55 - End of error messages (If you get this only, no errors were found)

The codes have since been erased and I am waiting for a few more key cycles to pull the new codes.

We are not exactly sure what to do anymore at this point. Any suggestions would be greatly appreciated.

 

Fuel should be 14.5PSI on a TBI truck.

Did you disconnect the ECT sensor before setting timing? If not, your timing is way off; disconnect it, let the motor warm up, then set to 10* BTDC (factory). IF you upgrade to a higher octane gasoline, you can run up to 14* to 16* BTDC; but these motors are tending to preignite on 87 octane with that much static advance.

If it is that far off, it might have had the timing chain jump a tooth; truck is old enough, after all. It's just not as common on the 5.2s as the 3.9s.

Don't forget to check the exhaust system! A plugged cat can make it run like crap too.

RwP

 

Would you please confirm that the ECT is the coolant temp sensor?

Also, would removing the cat and replacing it with a high flow resonator be an issue for the vehicle?

Thank you again!

 

ECT: Engine Coolant Temp.

You can pull the cat, without worry. Your PCM simply doesn't care about it.

 

It's the 2 wire connector sensor; the one wire under the A/C compressor is the one for the gauge. EDIT: Corrected, posted then remembered yours is a 1991.

RwP