2001 GMC Jimmy hard cold starting

OK. Here I am again with yet more Jimmy problems. Back in September my 2001 Jimmy (4.3L, blah, blah) wouldn't start. I did a complete tune up and it still wouldn't start. I changed the fuel pump and she started just fine and has up to now.

The other morning I went out to start it and it wouldn't start. It finally did start after much cranking and pedal pumping. After the engine warmed up it started immediately right on the first turn of the key, just like it should. It started fine even a couple hours later after it had cooled off some. However, after it sat all night, again it started very hard today, but once it was warm it started just fine.

The only thing that has changed is that the weather here has changed from very cold and dry to mid 50's and 60's and very wet. I put a full tank of gas in it and a bottle of complete fuel system cleaner. Any ideas? Before when it was the fuel pump it started hard no matter what the temperature all the way up until it just wouldn't start at all. I did notice that when it finally started this morning that there was a heavy fuel smell but I did pump the pedal just a little. Just thought you guys might have some ideas. I guess I should check the cold fuel pressure but I really don't think it's the fuel pump again. I bought a really good brand replacement and it's only a little over 3 months old. Thanks in advance.

Check fuel pressure and leakdown. Key to RUN, engine off, fuel pump runs for 2 to 3 seconds and shuts off. While the pump is running, pressure must be 60 to 66psi. Pressure must remain above 55psi for 3 to 5 minutes after the pump shuts off. Post your results.

OK I'm really beginning to think I have an ignition problem. For the past two days the truck has started just fine. Now today, it has rained here again, just like last Saturday when the problem started. My wife just called me and had a problem starting it. It has rained all day. I believe I should check the distributor cap, even though it's brand new, for looseness and cracks. What say you?

That's a tough call, intermittent problems can be difficult to diagnose. In your earlier post you mentioned a fuel smell: That could be from a lack of ignition, (the injector keeps squirting fuel flooding the engine). Check for spark at more than one plug. OR, the fuel odor could be from an internal fuel leak, (fuel line or regulator in the plenum). If you have a fuel pressure gauge, it's a quick, easy test.

yeah, I've got a fuel pressure gauge. I used it the last time when the fuel pump was bad. I hate these intermittent problems!! One thing I do remember though when I smelled the fuel was that I had tried to start the engine with starting fluid and still got no ignition. Before when it was the fuel pump the engine ran, just for a few seconds, on starting fluid. So, it's leading me to believe there is some kind of ignition problem. When it quits raining, if ever :) , I will test fuel pressure when it's acting up, if it does and report back. I might just replace the dist cap and ignition coil anyway. The cap is new but the coil is the original as far as I know. The cap could have a small crack in it I suppose. Maybe I'll take it off and shoot it up with some WD40 and see if the problem goes away for awhile.

I'll post back with some pressure measurements when I can.

Did fuel pressure test this weekend. Ambient outside temp @ 30 degrees, vehicle had not been started since the previous evening. On key turn pressure went to 60psi and stayed there for 7 minutes and was still holding when I removed the pressure gauge. I didn't have a problem starting it all weekend until this morning and then I got the hard starting issue. Sounded like some misfiring and I smelled the fuel odor as if it was flooding and there was no spark. I think I'm going to start looking into ignition issues at this time if you think that might be prudent. Vehicle had all new plugs and cap and rotor changed in September along with the fuel pump and filter.

Perhaps I'll change the coil and ignition module. Dist cap is clean and no cracks. I really don't believe there is a fuel problem considering it held pressure and I'm getting that fuel odor when I have these no start conditions. What do you think?

60psi is the bare MINIMUM. The fact that it holds pressure though, is a good sign. The low pressure could be a weak or broken spring in the fuel pressure regulator, or the pump is weak. You really need the fuel pressure gauge on it when it acts up to confirm or deny a fuel problem.

OK. More bizarre info. When the fuel pump went out before in September the only real symptom was hard starting until finally it just wouldn't start. It would not miss out on the road but would occasionally die, especically if the fuel was low. Keep in mind that this bad fuel pump was only charging the system to 40psi and had a bad check valve so the pressure didn't stay, but even with that, by some miracle the vehicle ran.

This problem is quite different since the pump charges to around 60psi even though I think it might be a little higher than that because I don't trust the pressure meter I have. And it holds this pressure indefinitely. Now for the new news:

My wife is the only one who drives the Jimmy. She drives one way 20 miles to work 5 days a week. The car starts right up in the morning, but when she goes to lunch she experiences some hard starting and missing out while driving. The same thing happens to her on the way home. I have never driven it and noticed the acting up. It does fine for me so I can't tell if the miss might be from bad firing or from not enough fuel. This problem just gets stranger every week. I have to do something about it this weekend though because I'm leaving on business for a few days. I'm not sure what to do at this point. Should I just change out the ignition coil, module and install a new cap and cross my fingers? If it would just exhibit the hard starting for me I would slap the pressure tester on it to see where it charges to. I'm just really confused. When I changed the pump I bought a good pump. An exact replacement from car quest, brand new, not remanufactured. So, any ideas? I really need to rid myself of this vehicle. It's driving me insane.

You can keep throwing parts at it or catch it when it's acting up and diagnose it. Intermittent problems are not fun, patience is the best tool in the box. ;) Do you have a scan tool that's capable of watching each sensor? If so, verify that the ECT, (Engine Coolant Temperature) sensor is reading correctly when the engine is cold. Compare the temp reading to that of the IAT, (Inlet Air Temperature) sensor. They should both indicate the same temperature when the engine is stone cold, (before starting in the morning).

Unfortunately I don't have a scan tool but I'm going to keep a close eye on things over the weekend. One thing I forgot to mention is that back in September when I did this mountain of work on the Jimmy I also changed out the fuel regulator (the part on the back of the injection module under the plenum). I'm not sure why I changed it. A long time GM mechanic told me that during his entire career he's only seen two of those fail and when they did they set error codes from oxygen sensors either bank 1 or 2 too rich or too lean. I don't have an SES light on. My wife told me this morning that the Jimmy started hard and idled very fast all the way to work. Any ideas why the fast idling? I've never seen an ignition problem cause that. I haven't seen it yet but hopefully this problem will show itself when I'm driving the Jimmy over the weekend. Thanks for all the advice.

A vacuum leak can cause high idling however, without the SES light on, it pretty much rules that out because it would set a lean condition DTC. Usually if there's a problem with the IAC, (Idle Air Controller) a code will be set also. Have you checked throttle linkage for binding, (not coming back to idle) or maybe a build up of carbon in the throttle bore?

You don't necessarilly have to have a scan tool to check the ECT and IAT sensors. You can check resistance between the terminals at the sensor. Both sensors use thermistors which change resistance according to temperature. When the engine is cold, (sitting overnight), unplug the connectors and measure the resistance. You're looking for the two sensors to be close to each other, not a specific resistance reading. If you post the resistance readings, I can tell you what temperature they are indicating...just to make sure they're in the ballpark.

Update and even more strange problems. I was away on business for a week but right before I left I took the Jimmy on a nice long ride. I noticed that it does miss out from time to time and when it does, the temperature gage goes down to 100, as if the sensor is receiving no input. After a while it comes back up to normal temperature. This only happens when the vehicle misses out. I also noticed that when I turn the key on I get no SES light. That happens only intermittently, sometimes I get the SES light with key turn and sometimes not. It never stays on, just during indicator diagnostics. Because of this strangeness I'm taking the car in for a complete diagnostic check on Thursday. A scan tool showed no error codes in the ECM but I think the ECM itself might be going bad based on these problems. What do you think?

If the temp sensor circuit grounds out, the gauge will go down, (an open circuit will make it go up). When the ECM sees a low coolant temp input, it will richen the fuel mixture which can cause rough running, especially if the engine is already at operating temperature. The Engine Coolant Temperature sensor is monitored by the OBDII system continously, which might explain the screwy SES light. The sensor itself may be operating within its range, in which case, no DTC's would show up. Might just be a faulty temperature sensor. The ECM is a very substantial part and rarely needs replacement. Post what the shop finds wrong with it.

I believe you may just be correct about the temp sensor. Back in September when I did all the work on the Jimmy the sensor accidentally came unplugged and the plastic that covers the pins partially broke off. I didn't think anything about it at the time but contaminants and water could get into the pins now and cause problems. I'm still going to the shop for the diag but this seems like a very logical explanation to me.

The ECT sensor is very easy to replace, (maybe 10 minutes), and very inexpensive. Might be worth the effort to replace it and see what happens, rather than spend a small fortune at the shop. If the sensor is damaged, it should be replaced anyway!

yeah, I'm thinking about foregoing the shop for now. By the time they charge the customary $50-$75 diag fee and then want to replace the sensor it will probably end up costing around $150 for a $12 part. I'm gonna try the sensor first and cancel my appointment for now. Do you know what size deepwell socket I'll need to remove the sensor? And how much coolant can I expect to drain out of the sensor port once removed? Thanks for all the help.

Match up the new sensor at the parts store for the size, can't remember what size ;) I usually relieve the cooling system pressure, (remove radiator cap and reinstall it) then swap the sensor quickly. The quicker you swap it, the less coolant you lose. If you're good, you'll only lose about a cup of coolant.

I replaced the ECT sensor today. Man was it a mess. It had shorted/gotten hot or something because the plug had some melted places. After installing the new sensor no more missing out :)

I still have the kind of weird SES light issue but I found out if I take the key totally out and wait a few seconds the SES will light on key turn. Perhaps it's always done this and I've just never noticed it. Also having no problems with the hard starting now. We'll see what happens. I'll post back with updates if I have more problems. Thanks for the help.

I had the exact same problem this morning. I have a 2000 Jimmy and it only has problems starting when it is below freezing outside. I ordered a replacement water temperature sensor but I am not sure where it is located. Can you give me some guidance to help find the thing so I can replace it? Thanks.

Owen

2000 Jimmy 4.3L engine, the ECT sensor is located right next to the thermostat housing.

I had the exact same problem this morning. I have a 2000 Jimmy and it only has problems starting when it is below freezing outside. I ordered a replacement water temperature sensor but I am not sure where it is located. Can you give me some guidance to help find the thing so I can replace it? Thanks.

Owen
Mine is located on driver side of engine just above the number 1 plug I believe (closest to the firewall). Took a 3/4in. deepwell to remove it. Kind of hard to get to but it fixed my problem. I hope it fixes yours as well.

Thank you for the quick reply!

I'm sorry but I'm very new to working on cars and I am not even sure where the thermostat housing is. Is it a part of the radiator? Or is it screwed into the engine block?

Mine is located on driver side of engine just above the number 1 plug I believe (closest to the firewall). Took a 3/4in. deepwell to remove it. Kind of hard to get to but it fixed my problem. I hope it fixes yours as well.

Didn't see your quote when I wrote my last one. Thanks a lot!