98 jimmy big problem HELP!!!

Ok here it is, I have a 98 jimmy 4x4 2dr with 134,000 miles.Alt is new, batt., k&n filter, fuel pump,water pump, pcv, ICM, spark plugs, wires, Dist. cap, rotor, fuel filter. So no codes thrown, one day after driving about 20 miles for about 30 minutes, I stopped at a store to eat lunch truck died after 15 minutes of idling. Would not start, for about 20 minutes. Finally started drove for about 2 minutes and died. Went back to pick it up after about three hours started drove it home 20 minutes away drove fine. Had the cat and exhaust replaced cause cat was goin bad, replaced with a bolt in magnaflow high flow cat and a 40 series flowmaster muffler dumped after muffler. Ran fine for 2 days. Drove again 20 minutes away at highway speeds died again. Replaced ICM started fine. drove home turned it off went to restart wouldnt. Finally got it to restart but after playing with the throttle pedal it hestates real bad. I'm at my wits end with this truck. I love the blazers I have three but I can't figure out whats wrong with this one. It seems to start after the truck has sat for an hour or two.
ANY HELP PLEASE, DON'T WANT TO GET RID OF IT. But I didn't pay much for it.


Ok now cleaned my MAF, and reset the ecm. Now doesn't seem like it will die but still stumbles real bad, in park and while trying to drive. Seems like no power.

As of today sat the 12th. I checked my plug wires to make sure they were connected still, took the egr valve, and blew out the build up, changed the egr valve with one off my other blazer (http://www.2carpros.com/forum/viewtopic.php?p=176608#). Drove it around thought it was ok drove it for 20 minutes beating it up. Ran great like new again. Thought everything was great and it was fixed, bout to shut it down and decided to wait till IAT got to 100 degrees or over. Since that's when it seems to mess up. It hit 102 degrees so I shut it down, restarted it worked fine but as soon as I stepped on the gas it would miss and act as if it were goin to die. Still stumbling and hesitating. And now won't start again. It seems to do this as soon as I hit over 100 degrees on IAT. HELP!!!

Ok just went back outside after letting it set for an hour. IAT is now reading 85 degrees when I started it. Started right up ran fine again, temp for IAT went down to 70 degrees runs great. So what could cause the truck to run like crap once it's at 100+ IAT ?????

Check fuel pressure. Looks like everything else for fuel delivery has been replaced exept for the fuel pressure regulator, located under the CPI manifold.

Just replaced fuel filter again. Still no luck still just turns off when IAT reaches 100-+ degrees.
How would the press. reg. make the engine turn off at 100 degrees?

ok so went out to start truck started up fine. Checked the fuel service line, fuel sprayed out when truck was running. Truck died no fuel would spray when pressed in key was on. Is this how it's suppose to be?? Or somehow could my new pump be overheating or shorting out???

Check fuel pressure and also for excessive leakdown. On 1998, just in front of the fuel pump relay, there is a single, recessed, empty terminal in the fuse panel. That terminal goes directly to the fuel pump. Connect a 10 amp fused jumper from battery positive to that terminal and the pump should run continously for testing pressure. Pressure must be 60 to 66psi while the pump is running, (engine off). Must remain above 55psi for 3 to 5 minutes after the pump shuts off. You can also check if the relay is switching from that same terminal. Post your results.

So ran truck tonight without airfilter. Same outcome, although tonight IAT never got to 100 degrees only up to 86 degrees. Still after about 40 - 45 minutes of idling and alittle bit of 15 mph driving around parking lot, engine still just turns off. I say turns off cause no stumble, no hestiation, no sputter just dies nice a calm like I shut it down. What would cause this. I've been debating weither or not to take it to a chevy dealership for a dign. but they told me if I'm not throwing codes then the diagn. won't really help. So i'd hate to just waste $100. Plus I don't trust other people working on my vehicles. Plus I'm a pretty good mech. I build hot rods and cars in my spare time. But this problem I just can't seem to fix and every other car person I speak to can't put there finger on what this problem could be. Nothing makes sense. Lets start fresh. Truck is a 98 jimmy 4.3 W vin 4x4 2 dr with 134000 miles on it. New: battery, alt. ICM, plugs, wires, distr. cap, rotor, K&N airfilter, running proper oil, new high flow cat., flowmaster 40 serious exhaust, new PCV, cleaned EGR valve, cleaned MAF, fuel pump, fuel filter. I seafoamed the engine and I run techron fuel cleaner about once a month or every other month. also run lucos in the oil.

Before the engine shuts off, the truck runs strong as hell, like new, MPG are great. Right before this problem truck was at 180-200 miles with over half a tank left.with mainly city driving on it.

Heed the Old master...the fuel filter and fuel pressure regulator are not the same part. Check the fuel pressure as OM and I recommended. There is a connector for this near the firewall on the fuel supply line. There must be enough pressure to start as well as maintain it. Jimmys are finicky this way...below abt 59 psi they are hard to start and after warming up, the regulator just might be crapping out on you.

The fuel pressure regulator is located under the plastic intake plenum and mounted to the fuel delivery "spider", on the back side towards the firewall. It's a little work to get in there, but not difficult.

Not worth beating yourself up over it. I had the same issue and had run the gamut of parts to replace too. Thankfully, we have some experienced people in here that helped me find the real culprit.

I know the two are different but I can't just go get a gauge to check it. And how would the fuel press reg. just stop working after warmed up, and not after it dies. THen work again after it cools. The reg. isnt elct. controlled right?

My apologies, I wasn't sure if you knew since in the earlier threads you stated you replaced the fuel filter again AFTER we suggested the regulator...hence the perception. Anyhow...

After rereading the thread many times, I don't see that the ignition coil itself was replaced. That may be another possibility for the sudden shut-down, though usually once a coil fails, its DONE. I've experienced a coil failure in another vehicle...you're dead where you sit. Why it would work then fail after heating up? Intermittent internal short? I dunno, but that's my next suggestion.

The big clue here is no SES light. That's why the dealer told you it won't help to do diagnostics on it. OBD monitors emission control, that's all. Fuel delivery problems and ignition failures, both primary and secondary, are not directly monitored by the OBD system. They cannot set DTC's and they cannot turn the SES light on. If your SES light works properly, the problem is not in the OBD system.

The fuel pressure regulator is a mechanical device, and has a very simple design. It has a diaphragm, a plunger, and a spring. When the diaphragm leaks fuel, or the spring breaks, it's done, there's no intermitent, it's good or it's bad. Checking fuel pressure will tell you if the spring pressure is where it needs to be, (provided the pump is able to overcome the spring pressure). If the diaphragm is leaking, it will show up in a leakdown test. Harbor Freight has a fuel gauge for around $15. Cheap, but it works.
Check your AF inbox for specs.

I have a coworker who owns a 99 jimmy 4.3l and he had a similar problem.
His truck would just randomly die on the road or just not start after some time sitting in the parking lot. He sprayed starting fluid in the intake and it would start/run for a few seconds then die and so on. He got his fuel pump replaced and the wireing from the fuel tank to the engine and still nothing. :banghead:

He finally noticed that if u would move the plastic hose at the MAF and the MAF the truck would come alive again.
So they ended up replacing the wires from the relay box to all around the engine and that solved the problem ! I guess it was a short somewhere !

I hope this helps !

....He finally noticed that if u would move the plastic hose at the MAF and the MAF the truck would come alive again.
So they ended up replacing the wires from the relay box to all around the engine and that solved the problem ! I guess it was a short somewhere !

I hope this helps !

Mass Air Flow sensor problems like this are fairly common. The ECM constantly monitors the MAF signal. If the signal is interrupted, even momentarily, it will illuminate the SES and set a DTC, guaranteed. Good thought though, thanks.

Took to dealership they say fuel pump. Wanted 1300 for it and labor. So does anyone know why a new fuel pump would work until truck warms up then drop to 44 lbs. When it was running at 65lbs. or do I need to just replace this pump again. It's new like 7 months old with about 1000 miles on it. ?????? Also What would the part number be for a 98 4x4 2dr jimmy vin w code. Just want to make sure I have the right one and not the one for a four door in it. And would that make a difference.

a bad ignition module will kill it as the module gets hot then as it cools down it will let it restart. also a bad cranksensor will do the same thing. but the part about no fuel pressure when it dies does point to fuel regulator. does the fuel regulator have a vacumn line on it ,if it does pull the vacumn line off and if gas comes out of the vacumn line hole the regulator is bad. could also be bad fuel relay getting hot look in the relay box find the fuel relay and see if another relay is the same relay as the fuel relay and swap the relays and see what it does . unless the fuel pump has been run dry without gas on it to cool it then could be just a bad fuelpump as these pumps are cheap made . and they want an outrageous price when you buy one. just my two cents worth of thoughts. but some dealers [ not all ] will tell you the fuelpump as to get a big job so they get get the big bucks coming in.so i would take their word for the fuelpump being bad without getting someone else checking it first.

no gas smell and no excessive gas usage. Dealership said it ran fine until warm then pressure dropped to 44 lbs. after warmed up then truck dies. So they say fuel pump.

Just because a part is new, is no guarantee that it's good. A fuel pump can fail no matter how old it is. Several things can cause a pump to fail: Faulty check valve, motor shaft seizing in bushings, armature wiring causing an open circuit when hot, poor electrical connection to the motor, faulty brushes, etc etc. A poor fuel pump ground or feed wire connection increases resistance to the motor itself, and will destroy it in a very short time also.

There is no "in between" with fuel pressure regulators, they're either good or bad. While testing pressure, if it regulates between 60 and 66psi, and leakdown is within specs, the regulator is good.

As far as pump number, it will vary depending on where you buy it. The 2DR and 4DR pumps are different, they are not interchangable. The fact that your pump has been replaced probably means the OEM identification sticker is nonexistant now. 98 2DR 4X4 ID number should be "SGK", give that number to your parts store, they will need it.

Well when I replaced the pump I didn't change the wire harness cause I couldnt find one at the time. Could this be the problem with this pump. And if so do you think this new pump is even bad or just messing up due to a wiring problem.

Most new fuel pump modules come with the updated connector. It's a different configuration so the original connector on the vehicle harness will not fit the new pump. It forces you to replace the connector. The new connector uses 14 gauge wire for power and ground to the pump. The new level sensor wires are still 16 gauge. The connectors they give you to splice it together are pretty cheesy. Solder the connections and put heat shrink tubing on, you'll never have a problem again. The problem with the original connector was that the wires were too small causing high resistance at the connector. When resistance increases, so does heat, the heat is what melts the connector. You can usually see the disfiguration in the original connector if high resistance is/was present.

the new type connector and harness came with my f/pump along with crimps and heat shrink. did your pump plug with same connector as old pump? or did you splice it?

The connector on the new fuel pump module is a different configuration so the connector on the vehicle harness will not fit the new pump. It forces you to replace the connector and do the upgrade.

yeah the pump i got had the same plug as the old pump and the harness. I mean the first pump that's in it now. Will replace with another one this weekend and the connector.

the last two fuelpumps i put in had the new type connector in the box along with the crimps and heat shrink and instructions on how to cut the wires. how long you had the last fuelpump, from what i read not long.should be some warranty left on it.but they still sell the fuelpumps with the old style square connector a neighbor just put one in his van.

Had this problem already in my 96 Jimmy. I tried every option that was listed here . I took a gamble with an aftermarket fuel pump( a bit cheaper ) from napa no problems since (6 years)