Moeron

My poor old 97 Laredo is showing its age. For some time, a couple years, it's had a condition, starts up, go run to the store.. after perhaps 15 minutes, the oil pressure gauge would drop to zero if engine rpm fell below 1000 or so. After 30-45 minutes it could at any time just spontaneously stall, most always at low rpm, at an interscetion, etc. and would stubbornly refuse to start [just crank, no coughs etc] until just letting it sit for 45-1 hour, and then it would just start right up. The thermometer reading is way out of line. The ODI is dead. All of this led me to suspect the ECU, since that seemed the central point where such things were controlled.

I just replaced the ECU [from Flashmasters] and well, nothing has changed. It cranks, but no indications it's actually trying to start, no coughing, no apparent smell of gas.. so I'm wondering what to look at next. Do the coils fail often? Does the ECU directly controls the injectors, or is there some other 'module' or such that actually drives the injectors?

Update: Looking in older posts, the crankshaft sensor looks like a possible culprit. Picking one up tomorrow. The very last time it did start, it ran very rough, stuttering for 20-30 seconds, then pffft.

Moeron

Well, changing the crankshaft position sensor took a while, and it still won't start. Fuel pump turns on, cranking it does no real coughing or almost starting, the fuel pressure at the distribution bar for the injectors is only reading 20psi, supposed to be 40 from what i hear. I really would rather not have to drop the gas tank.... the ECU is 'new', no fault codes, but if I run the "Test Results" I get a mix of success and failure.. I've looked around, but can't locate what these tests/codes are, can anyone shed some light here?

MizzJesi

I know this is kinda older thread, but I'm having same issue second time. First time was new upstream O2 sensors and relays and fuses.

Have you tried replacing your O2 sensors and checking your fuses and relays?

Cherryokee

A bad gas cap and/or vapor recovery (and purge canister) system can cause those symptoms. Keep your diagnostic steps simple. At first, take a drive with the gas cap loose to see if it has an effect on the described symptoms before/during/after. Be careful with any smoking materials while doing these steps .

Moeron

A gas cap preventing starting...? I can't "take a drive" anywhere until it starts

Cherryokee

Yeah. Check it out. If, when you uncork the gas cap, then do you hear a "swoosh" sucking sound? That's due to vacuum pressure that developed in the system because the cap is unable to vent. Give it a try and crank it up.

MizzJesi

I'm having the same issues as you, I just replaced my crankshaft position sensor, and it started and rove, but then died and blew the fuse again.

Here is the list of possible culprits I have found:
Cam sensor
Ignition coil pack
Ecm
pcm
bcm
Map sensor
Spark plugs
Throttle body
Crankshaft position sensor
O2 sensors

From what I have read on other threads, these all cause most of the same symptoms, and people have had luck changing one or others of these. Good luck, If I figure mine out I will let you know.

Moeron

the fuses in the power distribution block are ok, I hear the ASD relay click in. The crank sensor I had a mobile guy replace, I still want to verify a good signal, got a little handheld oscilloscope. I think I've identified the pins on the ECU to check, but they came from a 96 manual..

A7 Coil
C19 Fuel Pump Gnd
A8 Crank Sensor
A18 Cam Sensor

just been waiting for break in the weather mostly

MizzJesi

That's funny, coil was my next step

Moeron

I thought it sort of funny in the Haines book they say to check coil output, pull the spark plus wire from coil at the distributor, and hold a half inch above the engine block, to check for output. That's also a good way to get knocked on your rear. I haven't tried this yet, but if you have a compact florescent bulb, and hold it near the coil output (still connected normally) the bulb should dimly flicker from the high voltage field without having to expose bare spark wire....

MizzJesi

that's just nuts! Think I'd I'm questioning that bad, I will just replace it. Lol never hurts to upgrade or replace older parts

snagster123

any positive results from your trial and errors?

MizzJesi

Well for mine, after replacing the cam and crankshaft sensors and still getting a no start, I learned that the PCM would need to be reset in order for itnto register the new sensors, resetting g did work for me.