Was running great.... now won't start

[robertisaar]

there's a pretty good chance that the ADS file you're using for TP to scan the camaro PCM came from me... if you find something wrong with the datastream, LMK.

[CNCguy]

Wait... what is that?
The wires to the crank sensor are in different places!
The plug on the ICM that runs to to crank sensor is a 3-pin plug. On the Camaro the two wires are connected to the middle pin and the one farthest from the 6-pin connector. On the Olds, the wires are connected to the two outer pins of the connector - the middle pin is open.

If you look at the diagnostic wiring diagrams I posted last week, you'll notice the diagram shows the wires with a not-connected center pin. hmmm.

It does seem strange but both vehicles use the same P/N ICM. Diagrams for some cars also show a shield being connected to the third pin. One would have to assume that pin "A" is the "High" signal while pins "B" & "C" are grounds and the "Low" signal wire can be connected to either pin. Not keeping everything standard is standard for GM.

[Syclone1452]

Yesterday, I bought a PCM from a local bone yard. They gave me a 2-day return window for it. I took off work this afternoon to mess with the car. That "new" PCM won't start the car, either... big surprise

The RPM value is 325 all the time... when cranking or not.
With the other PCM it was 300... odd

there's a pretty good chance that the ADS file you're using for TP to scan the camaro PCM came from me... if you find something wrong with the datastream, LMK.

It looks like there is a problem in the ALDL definition file.

RPM is defined as byte 41
... but... so is A/C Pressure... oops

I did some playing around, and I think byte 40 may be the RPM

I don't want to tell you how many hours I've spent banging my head against the wall... thinking the PCM wasn't seeing RPM. Granted, once I got the o-scope on the PCM, I determined there really wasn't any square wave, but it makes me feel better if I can blame someone else.

Now... how do I check to see if the timing chain has jumped or something like that? Remember, this engine has over 160,000 miles on it.

[Syclone1452]

I just connected the original PCM.... still no start
While watching byte 40 for RPM, it is zero when turned on, then jumps around while cranking... up to about 450 rpm... then drops to zero again when I stop cranking.

What do you think the odds are of me getting my money back at the salvage yard?

[Syclone1452]

I took the PCM back. They wanted to give me another one. I said no thanks.

I got store credit. That's fine. I have more vehicles in the driveway that will need parts before long.

A neighbor came by and looked the car. We tried to start it... He agreed that it wants to start, but just can't quite make it there. He doesn't think it's a timing chain issue. He told me to clean the plugs and try again.

... i'm off to clean plugs...

[Syclone1452]

I finally got it started...

I cleaned the plugs and cranked it until I was blue in the face.
I noticed my fuel pressure gauge was reading a bit high... like over 50 psi, so I kept cranking.
once it started, the fuel pressure dropped to between 40 and 45... that's way too high

I put a vacuum gauge on the regulator and pulled btwn 20 and 25 inHg. It starts easier, but still won't idle well at 40 psi of fuel pressure.

Do you think it's my fuel pump or the regulator? Remember, I have a high pressure 255 lt/hr fuel pump in it.... but it ran fine for several weeks with that pump...

[robertisaar]

i would look at the FPR... the return line should be more than enough for the regulator to keep the pressure down to where it should be.

and you are entirely correct on the RPM being byte 40. my bad.

[pocket-rocket]

Alldata does specify 41-47psi at the rail, but that's key on, engine off. I wonder if your return line got pinched in the whole head gasket fiasco.

[Syclone1452]

R.I.P 3.4

Last week I managed to get it started after MANY tries. It just wouldn't run right. I noticed it has a LOT of blowby, so I did some reading. Folks say it can be rings stuck.

Today, I started car [after many tries]... got it warmed-up... drove it up the road and back... wouldn't idle... had to keep it at 1500-2000 rpm all the time.

I then did a SeaFoam treatment... at 1500 rpm. I let it soak for nearly an hour. It took FOREVER to get it started again. I took car for a ride. SeaFoam says to drive agressively, so I got it to about 50 mph, and mashed the gas. It downshifted, and the RPM wouldn't go over 4200 or so unless I kept my foot in it... Didn't hear any knock or anything like that... just wouldn't rev. I turned around and tried it a couple more times... nope... takes forever to get to 4500 rpm

Then I noticed the oil pressure... which is usually around 60-80 psi... dropping like a rock.
Yep... went to zero and stayed there... yep... "Check Gauges" light and all....
I shifted to N and let it coast... engine died...
I coasted into my driveway...

...throwing hands up in air...

...using some special "sentence enhancers"...

...walks away from car with smoke coming out from hood...

Anyone want a really nice '95 Camaro paperweight / yard art?

R.I.P. 3.4

[pocket-rocket]

You know, after Sea Foaming my wife's 95 T-bird 4.6, it wouldn't hold pressure well after that either. I was going to try a new oil pump because it's not too hard in that car being behind the timing chains in the 4.6l.

[deathamatend]

Two things to point out. 1. any time you use Seafoam in an engine which is not regularly "Seafoamed" you alway run the risk of a lot of sludge, grit, and debris in the crankcase being dislodged and circulating in the eingine oil. Remember oil is filtered AFTER the oil pump. I would wager that the oil pump presuure releif valve is stuck open with crud that was sucked into the oil pump pick up (or oil pump pick up screen is clogged with crud) during the Seafoam event. 2. The oil pressure gauge sender also has the FUEL PUMP CIRCUIT pass through it for engine protection from no oil pressure. So no oil pressure will mean no fuel pressure. All the dash lights come on like that when you RUN OUT OF GAS, which is essentially what just happened. FWD GM's engine oil pans should drop down without too much trouble. It is easiest way is to use a 1/4" drive socket set with a 1/4" drive 12" extension. 10- 15 minutes tops to remove all the bolts. AND they make a one-piece moulded silicone pan gasket! A trick to try is, if you can get a oil pressure sender SOCKET and remove the sender, have a helper crank the engine a few times with sender removed (Don't let engine run) to blow out main oil pump passage, oil pressure might return to normal. If not just drop the oil pan and put in a new oil pump, it's not worth it to risk the motor over no oil pressure.

I would not make too much over the fuel pressure, 60 PSI is the upper service limit I have seen. If the fuel pump is new and high volume, the readings you are getting at the fuel pressure tap on the fuel rail all within service limits. Did you check the vacuum reading at idle? If the engine will not idle I would check the Idle Air Control motor for a stuck rod or a blocked orifice, or some other similar problem. (this would be a NO CHECK ENGINE LIGHT problem) And run ALL vacuum lines, rubber and plastic. A decent size vacuum leak will not let this size displacment engine have an idle. An important note: Using a vacuum pump to increase the vacuum on a fuel pressure regulator wil RAISE fuel pressure. When you "floor it" engine vacuum drops and drops at the fuel pressure regulator which raises fuel rail pressure and volume.

[jwvess00]

Hi there!

Point of order -- the fuel pump oil pressure switch will NOT kill the engine if you lose oil pressure. The oil pressure switch is in parallel with the fuel pump relay. If the fuel pump relay fails, the oil pressure switch will keep the fuel pump running. If you lose oil pressure or the oil pressure switch fails, the fuel pump relay will keep the fuel pump running.

The oil pressure switch is there because GM didn't trust the relay, not to shut the engine down for low oil pressure.

Don't believe me? Unplug the oil pressure switch and start your engine. It will start and run.

[deathamatend]

I was wrong about fuel pump circuit here is the wiring diagram. If you would like to test the fuel pump directly without any other circuits or relays involved, there is an orange w/black trace single lead wire as shown in the fuel pump circuit diagram. You will find it in a harness loom near the winsheild wiper motor, on the firewall. If you energize this connector with 12V+ battery voltage (key on or off) the fuel pump will activate and run for a pressure check (it will run the engine if cranking and no other probems present)