Hi All, The only car that I will probably write about here is a 1988 Buick Regal
Custom - 2.8 Litre MPFI Automatic. Odometer stopped working at 144,000.
Might have 160,000. miles, but I really doubt it'* that much. I usually drive
the car once a week for short distances mostly. A rare busy day sees
75~ miles. A normal day will be 35~ miles. I've owned it for about 12 years.

I'm kinda stumped about a couple of things on this car lately. Since I
decided to keep this car, even though it wouldn't start recently and I don't
like to be broke down, I've started to invest in replacing stuff. I've nearly
replaced everything from the tip of the tail pipe to the ECM.

What'* baffling me (mainly) is, I'm getting a code 64 MAP Sensor Signal
Voltage Low. Well, I went as far as digging into the engine wiring harness to
check for a shorted wire. Everything looked O.K. Then while investigating why
I wasn't getting feedback from the MAF sensor on the scanner, I had the
MAF sensor unhooked and noticed that the MAP sensor was now properly
showing 5 volts on the light green signal wire. After studying the wiring
schematics, I see the only physical relation these 2 sensors have to one
another outside of the ECM is a shared ground Pre-ECM. The individual
wiring harnesses run separately. About a foot or so away from the ECM, the
harnesses split. The MAP wires run around the front of the engine and MAF
wires run along the bottom of the Radiator. They have separate grounds in
the ECM. Both circuits test good individually. I have tried 2 diff MAP & MAF
sensors. The MAP readout is not good while the MAF is connected. MAP is
O.K. with the MAF disconnected.

Overall, I have a rich condition. The Spark Plugs are black. This is a recent
condition. Before, the plugs were nice and tan throughout the history of this
car, even while the O2 sensor was broken for a year and a half (broken in the
manifold - now replaced). Now, the car will not start without depressing the
accelerator. Then it misses horribly until I punch the gas a few times and
slowly bring it back to idle. Then it idles alright, but I can hear a miss in
the tailpipe. I've got 3 injectors on order. I already replaced 3. Since these
injectors are 25 years old, they are probably leaking. 2 were dead of the first
3 I replaced (one in each bank).

Also I'm getting no feedback from the Coolant Temp. Sensor (CTS) on the
scanner. The CTS is new and the circuit tests good. I called GM about an
Engine wiring harness and of course the prez has stopped production of
parts (and crushed many donor cars for China). Can't even get GM wiring
end kits with seals.

Another problem I see on the scanner is, it is rapidly shifting in and out of
overdrive while in "Park", whether the engine is running or not. And it always
reads 2nd gear as being engaged, while in "Park" - engine on or off. I don't
even know where a related sensor for this might be. Haven't had time to
examine that yet.

All wiring grounds seem to be secure and clean (oil coated too).

I think I have an overheating problem for a long time now. I have to
occasionally add antifreeze to the overflow tank (keep a gallon in the trunk).
No water in the oil problem. The only time I've heard the fans kick on in a
long time is when jumpering the ALDL "A" & "B" terminals. I replaced the
Primary Fan Relay the other day. Haven't run it enough to know if that
helped. I'm thinking this problem is CTS related.

The scanner is an Actron CP9190 (the CP9185 w/ all the cables &
connectors). Is this scanner reliable or is my car wacked?

It always helps getting things sorted in my mind by writing everything down,
so I'll put a list below. Being an old Mechanic, I've learned to keep good
records!




LIST:

To date, all external engine components have been replaced, except for the
Canister Purge Valve, 3 injectors, plugs & wires (I'm replacing ignition wires
when the new Injectors arrive, even though the wires Ohmed out O.K. - no
signs of arcing problems on the plugs - might keep the plugs for a while -
we'll see).

ALL NEW PARTS:

Completely rebuilt the Rear Suspension & painted with SPI Epoxy Primer
(2011 - unrelated; don't try to make a truck out of a car!)

Complete Exhaust System replaced (2011 - probably less than 2,500 miles
since then)

Crank Position Sensor replaced (2012 - probably less than 1,500 miles since
then)

Water Pump replaced (2012)

-------------------------------------------

RECENT ADDITIONS (SINCE JULY 2013 - 000.000 MILES ON THE CAR SINCE
MID JULY)

Fuel Tank & Delphi Fuel Pump Assy. replaced (Pump Assy replaced twice. The
Fuel Gauge doesn't work on either of the new Pumps. The old one worked.
(The old pump wouldn't hold pressure). Gotta check the gauge after I get
the engine running right.

Fuel Pressure Regulator replaced (old one still good - goes onto the
"in-stock" shelf)

Fuel Pump Relay replaced

Fuel Filter replaced

Steel Fuel Lines from the Fuel Tank replaced (the old ones were really rusty
like the top of the Fuel Tank (pin hole in the old tank. Painted the top of the
new Tank along with the new Fuel Lines with SPI Epoxy Primer) Rubber
vent Hoses also replaced.

Replaced both Fuel Line Flex Hoses (Feed & Return) going to the Fuel
Pressure Regulator (the old Feed Line was collapsing).

3 Fuel Injectors replaced (2 bad - 1 speced out O.K. on a cold engine, but
was a little lower in Ohms from the others, yet still within specs. Decided to
keep as a 25 yr. old spare. 2 other injector wires were rubbed through on
the Plenum down to wire. This was on 2 different injectors than the ones
replaced; so 4 injectors had some sort of problem. The wire problem made
me want to replace the ECM, also because of the other weird readings I
was seeing.

ECM replaced (old one might still be good, but I don't trust it yet) I've still
got the original ECM, which is most likely still good. In all, I've tried 3
different ECMs to troubleshoot with - No noticeable problem in any of them.
I usually keep old cores when I suspect they are still good or repairable)

Ignition Control Module & 3 Coil Packs replaced (old ones probably still good,
but replaced as a preventive measure - replaced 1 of those coil packs
about 9 years ago; the others stuff there was all original).

EGR Valve & EGR Tube replaced (tube is a new custom made all stainless -
old ones were bad). Will use the old valve to make a "block off plate" should
I ever want to get rid of the EGR valve. There wasn't much carbon anywhere
initially. The old EGR failed on the vacuum tests.

MAP Sensor replaced (old one still good - goes onto the "in-stock" shelf)

MAF Sensor replaced (old one good? - bad?)

Coolant Temp. Sensor replaced (old one good? - bad?)

PCV Valve & Grommet replaced (old one good for being 25 years old, but both
valve covers had bad leaks, so I replaced it).

Replaced Vacuum Hoses as necessary

Throttle Position Sensor replaced (old one bad)

Idle Air Control Motor replaced - cleaned bore seat in the Throttle Body
(old one still good - preventive measure thingy - old one goes onto the
"in-stock" shelf)


All in all, the engine ran much smoother BEFORE doing ALL of these
replacements, but of course the engine would soon die and would not start
again until like an hour or more later. Now the engine will start after slightly
pressing the pedal down and working the throttle after it hits, 'till it idles
on it'* own. The engine doesn't die now, but I don't trust it enough to
drive it yet.


Any ideas on "what in God'* green & blue is going on here" with the scanner readings?

if you are loosing the power to these sensors its likely they are connected internally in the pcm. so anything that is powered the same in the car could be partially taking the power. something like corrosion or water in trans connector or any other connector for that matter. i guess i would pic up a can of contact cleaner and start taking every connector apart pull on the wires to make sure they are tight, spray them with contact cleaner and a few good shots of compressed air, might do this a couple times to be thorough. would also clean the grounds on the engine and chassis. could have multiple issues with an older car. but if your supply power is going down to the sensors that will mess everything up, i would check and clean the power and grounds to the pcm as well

Thanks for answering JW. Multiple issues indeed.

I've got the 1st edition of the FSM so if there is a connection to the MAP & MAF in the ECM, it is missing in my manual. I'll do as you suggest on checking the grounds. As wacky as this car is, it is probably a headlight ground wire causing the problem. After I find the transmission connectors I'll check them since I have a couple of strange readings in that area. I did notice the power steering pressure switch was GONE. The connector is there with part of the switch attached to it, but the part of the switch that connects to the steering gear is gone. The rubber seal for the switch was still stuck on the steering gear, but from the look of things, this was gone years ago and the car has hauled many heavy loads and given many pleasurable hours since then. I'll remove the remaining part of the switch from the connector to see if that helps.

Thanks for your help JW, I really appreciate your input!

not sure how they are inside but sometimes if you have a short or partial short in wiring it becomes a resistor and drops some or all the voltage on the whole circuit depending on how much other loads you have. so if you have one 16gwire feeding the pcm, inside it feeds that out to the maf and map and other things, so if a connector like the ps pressure switch or trans connector wires had some junk or water in them it would take the total power down to wear nothing works properly

It'* always good to remember those basics. Getting too technical (for 2 months) can blind me sometimes. I have checked all of the sensor connections and twisted & poked around the wires at the ECM and sensor ends with the scanner connected and have seen nothing obvious other than the MAF dropping the MAP signal while both are connected - plus the CTS giving no feedback whatsoever. The funny thing is all of these circuits test O.K. individually. I'll get the magnifier out and look closer at all terminals on both ends too.

I guess the primary concern right now is checking the power train and steering sensor connectors, plus the grounds as you suggest. If that produces no results I'm thinking of running my own MAF harness to the ECM, but I'll have to see if that'* possible in the schematics; later.

I have the new injectors now, but I can't put the plenum back on 'til I get these sensor problems sorted out. I think I'll even disconnect the injectors while I shoot these issues. Come to think of it, unhooking some of the other sensors while checking the CTS might help.

Thanks JW!

Well, I spent some time today checking ground points. I don't think the guys who
voted on putting 2 grounds on the side of the block by the firewall even want to
go to Heaven, 'cause that is nothing short of pure evil. Out of 5 ground points,
the one on the body which runs to the engine was a little corroded (below the
battery). I used the air buffer to shine everything up there. The ECM is grounded
to the Engine block and the block grounded to the body/frame at that point.

As far the Power Steering Pressure Switch goes, I think I now know why my Air
Conditioning stopped working about a year after I got the car. This switch is
suppose to be normally open (NO) until the pressure reaches 500 PSI. The way
the broken switch was still connected to the harness, it was perpetually CLOSED.
The ECM thought I was going around a sharp turn for 11 years, and switched the
A/C Comp. off! Back when the A/C stopped working, I didn't own a FSM or a
scan tool, so I wired my own switch to the relay and flipped the air on and off
whenever I wanted. This is the last thing I'll fix; then remove my big orange
A/C switch wiring - hopefully.

I'll do some tests the next time I work on it. Stay tuned.

didnt know it did that.

Wish I knew a lot sooner. I'd like to see a "cut-away" view of that switch, 'cause it looks like it'* designed to be NC instead of NO. There must be an actuator pin missing which makes it NormOpen.

I said the PS Switch was gone, but it was separated where the plastic and metal connect together. Of course, if it was gone, the fluid would be gone too. I can't even imagine how this switch broke.

I believe those switches are built just like the oil pressure switch on the 3800'*. Below that plastic housing, is a plastic diaphragm that pushes against an electrical switch. If the black plastic breaks off, the diaphragm can still hold the fluid back.

Just like this one. You can see the plastic inside the metal part on the upper left...