I have a 1992 F-150 5.8L automatic. The drivability is much poorer when the ambient temperature is higher; say above 50F or so, than below. During the cold snap we had here in February, it ran very good. In warmer weather, it will intermittantly stumble and hesitate. When this occurs, the check engine light comes on, but goes away fairly quickly. Also, there are periods where the transmission shifts very harshly, and other times normally.

I'm going to dig into this over the weekend, and try to pull codes, do a visual inspection for anything obvious, etc. But if anyone has any ideas on specific or common things to check that are peculiar to this year/engine, I'd appreciate the input. The truck is virtually all original except for plugs, wires, cap & rotor which I changed last year.

Any ideas on where to start looking will give me a leg up on diagnosis.

Thanks!

JD

 

Start with codes before speculating on parts.

 

Yeah, I'll be pulling codes this weekend, and will post up what I find here. Just thought there may be a common issue with these engines that I wasn't aware of to check first.

Thanks,

JD

 

It seems like any of the air related sensors is getting clogged or weak, as you check codes, you could also clean the IAC, just to check if there are any changes.

 

my truck has always ran better when the temp is below 20 degrees not sure why... mine is an I6 though

 

Here are my codes, and what my code reader manual says they mean:

No hard codes indicated, which I knew already since the MIL isn't lit continuously.

Continuous Memeory Codes:

327 - EGR valve position circuit below minimum voltage
328 - EGR closed valve voltage lower than expected
332 - Insufficient EGR flow detected
542 - Fuel pump secondary circuit fault
634 - Manual Lever Position sensor voltage higher or lower than expected or A/C on [it wasn't]

Obviously, there's an EGR issue effecting drivability. Are there any checks I can perform to determine if I have a faulty EGR valve assembly, or if there is a wiring or electronic problem?

The fuel pump circuit fault puzzles me. Anyone know what that one's about?

The Manual Lever Position sensor may be the root to my harsh shifting issue. Is this the flat component bolted to the LH side of the transmission near the pan rail with the harness connected to it?

Any and all input is appreciated.

JD

 

Bump......

 

Another piece of information; since most of the codes deal with the EGR, I disconnected the vacuum line at the EGR valve and plugged it. Now the truck seems to run and shift normally; MUCH better. Other than the constant "CHECK ENGINE" light (which I expected) it seems to have corrected the drivability issue.

Which component is bad; the EGR valve itself, or the sensor on top that's plugged into the harness?

Thanks,

JD

 

I would try to clean the EGR valve, if that didn't do it, i would replace the sensor. search for any broken wires on the sensor and check those vacuum lines for leaks.

 

Your EGR issue looks more like a collapsed diaphragm than build up on the pintle seat, but it never hurts to inspect and verify. Before blindly replacing anything meter the EVP output to verify the signal value with the EGR closed. Then apply vacuum to see if the EVP signal increases to the expected value.

Yes, the MLPS is located on the driver side of the transmission. Some good MLPS info in here: E4OD MLP adjustment? - FSB Forums

 

I have the FSM, and will research to find the spec values for the sensor. I picked up an EGR gasket today, so I'm going to pull it off this evening and inspect/clean. After a drive test, I'll post up my findings.

Thanks!

JD

 

I've already checked the alignment marks, and confirmed they're right. I read E4OD link, and gathered the following:

1) Back-probing will confirm if the MLPS is adjusted correctly, but it didn't say which wire(s) to probe.
2) The 1995+ MLPS is prefered as an upgrade to mine (1992).
3) A pin change is required to upgrade to the newer-style MLPS, but it wasn't clear which pins needed to be switched to where. I assume the second diagram in the link showed the pin layout in mine, and the third diagram showed the 1995+ layout. If so, then I'm clear. If not, please advise.

Also, where do I buy a new MLPS? The usual places don't list it, so I'm assuming it's a stealership item. What kind of cost am I looking at for a new one?

Thanks!

JD

 

The pin-outs are the same regardless if it is 1995+ or earlier. Ford in their infinite wisdom changed the connector. The diagram Steve83 has shows the MLPS for different model transmissions. The one labeled E4OD is the one you want.

You need to measure the TR Sensor signal between pins 2 and 3.

You can purchase an aftermarket MLPS but many of the part houses list it as a Neutral Safety/Range Switch. The Motorcraft Part Number is SW-5978. This is the kit to upgrade to the 1995+ MLPS w/new connector.

 

Thanks for the continuing information. Here's what I found tonight:

EGR Valve:

1) Checked and confirmed the vacuum line is good.
2) Put a vacuum hose on the diaphragm, and sucked to check operation. Pintle moved freely and smoothly with no binding. Held vacuum with no leak-down.
3) Pulled the connector from the sensor and confirmed clean pins and sockets.
4) Removed the EGR assembly and inspected the seat. Again sucked to check operation; all good. Checked to confirm the EGR valve seals tightly with no vacuum applied.

Overall, the EGR valve looks pretty clean, and didn't have much deposit build-up. I put it all back together and checked the voltage. Since I don't have the values, I found one of the three pins that varied voltage with vacuum and recorded the values:

Closed/no vacuum = 0.41 VDC
Open/full vacuum = 4.43 VDC

Don't know if this is the right pin or values, but the DVM moved smoothly up the scale between the values noted as I applied vacuum from full closed to full open. Seems to be working properly. If you have the manual specifications for the values, please let me know.

Everything seems to be working correctly, which doesn't help lead me to my problem. Is there a chance that just pulling everything apart, cleaning, and reassembling may take care of it? I'll be driving it the next couple of days to see if the drivability issue reappears.

MLPS:

I'm leaning toward buying a SW-5978 since it seems like a fairly common failure after doing a little research. RockAuto has them for around $52.00. Hope that fixes my harsh shifting issue. First, I'm going to double-check the adjustment (mechanically and electrically) on my current one.

Thanks for the input.

JD

 

Ford Fuel Injection » EGR Valve Position sensor (EVP)

0.41VDC looks a little low according to the chart Ryan has posted.

Stick with your MLPS plan. Measure/adjust as necessary as well as clean the connections. Then replace if necessary.

Make sure the TPS output signal is linear as well. For reference: Ford Fuel Injection » Throttle Position Sensor (TPS)