Like the title states, I have a '95 Blazer, 4.3L Vortec that will barely run when cold. (engine temp, ambient air temp has no effect.) The engine will backfire, the throttle is very unresponsive, and the throttle has to constantly be manipulated. If the engine is kept running long enough to get close to operating temperature, it smooths out and will maintain idle, and can be driven normally. The temp gauge barely ever moves off the 100* line.

I have replaced the fuel pump (AC Delco), spider and regulator, and "nut" kit. Also, the cap, rotor, wires, and plugs were replaced with new AC Delco parts. I have tested the TPS and it is good. Also, I replaced the IAC valve, but returned the new part when there was no improvement.

I had the coil and ICM tested today. The coil tested good, but the ICM showed bad. However, since there was no plug that fit it, he had to manually attach clips to the four pins. I've been reading about the ICM, and it seems that if its bad, the engine will not run. Since mine will run, I am doubting the accuracy of the test.

The CEL is on, however I have not been able to retrieve codes from it. My cheap code reader will not communicate with it, even though the truck is OBD 2. (computer under hood, OBD2 connector). The truck is not registered nor inspected, so I dont want to risk driving somewhere to get codes pulled.

Thanks for any help. Sorry for the long post, just trying to give enough info to help solve the problem. Ive searched this site, but it seems like everything is the opposite; running great when cold, but bad when warmed up.


Edit: it reminds me of an old carb'ed car, where the choke isn't working. Do these electronic engines have some sort of "fuel enrichment" function?

 

Yeah.. it's controlled by the ECT, Engine coolant sensor primarily. Since the engine wants to die {low rpm} instead of idling too high when cold, probably not a vacuum leak.

If it's running too rich, cold, you should catch whiff of raw gas. and find wet plugs. Assume you've done fuel pressure leakdown test.

So.. you have a MAF. Try disconnecting it {the wiring connector} before you start engine cold and see how it runs.

 

Thanks for the quick reply! I don't think I have a MAF, though. The only sensor in the intake air ducting I thought was the intake air temperature sensor. Unless that is the MAF?

 

If it's just IAT will only be two wires. If you dont have MAF, ohm out your IAT and ECT {no I dont know which one.. no one on here seems to be certain, but it's the one that's not for the gauge}

Measure between the two pins.. should be very high ohm or infinite either pin to chassis grd.
Also COULD be MAP sensor I guess but think they dont run right warmed.

USUALLY if these things read correctly cold, they are good.

 

It would be extremely helpful if you could retrieve the DTC's and post them. 1995 used 3 different OBD systems, (one of the reasons why GM did not produce the Bravada in 1995). The fact that you have an OBDII connector and a "nut kit" means the vehicle is equipped with what's commonly called OBD1.5 and is not fully OBDII compliant. It requires a scan tool capable of communicating with that system. The el cheapo scan tools that the auto parts stores use won't do it.

If coolant temp does not reach 195F, that needs to be diagnosed and repaired first. That might be the entire problem In your first post you mentioned replacing the spider, nut kit and fuel pressure regulator but there's no mention of fuel pressure and leakdown, either before of after those repairs....Turn the ignition switch to the RUN position, do not start the engine. While the fuel pump is running, fuel pressure must be 55psi to 61psi. It must remain above 50psi for 10 minutes after the pump shuts off. Post your results.

 

I did the leak down test before the fuel pump repair. It was losing pressure pretty quick after turning off the engine. I haven't tested it after the new pump was installed, but I have seen fuel in the lines of the nut kit after sitting for several days. Before the lines were empty. And the truck fires up the first time after the new pump, before I would have to "prime" it by cycling the key for several minutes to get it to start.

I wish I could get codes for it! Would really help me. The computer is on the passenger side inner fender. I have read this means it is obd 2. Could it still be obd 1.5?

I'll ohm out the ect or iat. Thanks for that chart!

 

Absolutely OBD1.5, CMFI, (Central Multiport Fuel Injection). It uses one fuel injector and the "nut kit", no doubt about it.

OBDII is CSFI, (Central Sequential Fuel Injection). It uses 6 mini injectors and no "nut kit".

Very few late production 1995's have OBDII compliant systems. All 1996 and newer have CSFI and are fully OBDII compliant.

 

Can I jump pins with obd 1.5 and retrieve codes like you can with obd 1? I have the 16 pin obd 2 connector, however, not all the holes are populated. If I can get codes from this thing, it would greatly help in figuring out what's wrong with it.

It definantly has one central injector and 6 poppets at the ends of the tubes. I assume it's called the "nut" kit. It's the feed and return lines to the injector inside the plenum.

 

Unfortunately codes can not be retrieved without a capable scan tool on OBD1.5

Check out the low coolant temperature, it might just be the thermostat is stuck open slightly. The PCM watches for coolant temperature to achieve operating temperature within a predetermined time limit. If it doesn't, it will set a DTC. Low coolant temp will cause performance and fuel mileage issues.

 

Turns out the gauge was correct in showing a ~110 degree reading. Two thermometers in the radiator showed 117* with the thermostat open. Im kicking myself for not replacing the dang thermostat when I replaced the water pump! So that solves the cold running issue. Do you guys think this could cure the horrible dive ability when the engine is overnight cold? Probably won't have a chance to replace the t-stat until the weekend.