I've got a 97 D1, GEM's truck. Lately, I've been have a problem with a misfire. The truck seems to idle normal, but as soon as you give it just a little gas, it starts to cut out, and backfire through both the intake and exhaust. Thing is, it does not do this all the time. It does not matter if the truck is hot or cold, either. The truck can be driving fine, and I'll stop at a light, then it will start acting up. 10-seconds later, it's normal again.:mad3:

So far, I've changed the MAF sensor, fuel filter, and coil pack. I've checked, and rechecked all wiring harness for water/damage, and I've checked the ECU for anything noticeable. All look fine and normal.

Only other thing I can think to do is swap crank sensor, cam sensor, and fuel pump. Is there anything thing else I should look at first?

In the mean time, I'll reset the codes. The check engine light has been on for four years, so I'm sure there are a TON stored.

This is getting aggravating!

Sticky valves?

I'd vote for sticky valves as well.

Make sure you check the fuel pressure before taking anything apart...

It should bump up some when you pull the hose off of the pressure regulator too.

Too be real professional measure the volume coming out of the return line with the engine idling.

I'm at home so I don't have specs handy.

I did two fuel pumps in a row last week,trucks ran fine 80% of the time.put a guage on them and they were 30 psi max,even with return line blocked off.
Electrical waveform of fuel pump was good on both.(no dead segments of the motor)


Not saying it's not sticking valves,just try to work from easiest to hardest fix.

sticky valves....... with bacon.

....or fuel pressure.....or like one I had recently where the inside of the ECU looked like a green fuzzy sweater factory

GEMS is fucking awesome right up to the point where it isn't....what is it, re-learn adaptive values or sumthin' like that. There ya go PT, back to beating on Rovahs. It does feel better.

is there no cooperative specialist with Autologoic or Local dealer that will read the codes for you? The local here will read the codes for $75.00 which saves just chucking parts at it, those codes can be valuable.

sticky valves....... with bacon.

....or fuel pressure..... those codes can be valuable.

I had a Shopboy (not Shopboy, Shopboy, but A Shopboy) who had these crazy misfires... He threw a head job at it, no dice. Took up the main bay of the shop for nearly a month until I happened to walk past and suggest checking fuel pressure... Then came the debacle of cobbling a fuel pump together to avoid the $600 dealer part or near $500 aftermarket alternative.

I'm with Don, some may say the pumps won't start to pump lower pressures, but I've seen 'em get real low pressures and the engines throw misfire and lean codes and it turns out to be low fuel pressure from the pump assembly.

My favorite part is that the diagnosis is darned near free, pull the valve and screw in the gauge...

PT,
speaking of cobbling together fuel pumps. Have you had any long term luck with the AC Delco pump that has the same specs (don't have the part #handy)?
It seems as if the original equipment pumps will last 15+ years( if you change the fuel filter when you're supposed to) yet I can't seem to get much more than a year out of any of the other sustitution pumps. I'm at the point where I just spend the extra $$$$ for the genuine article.

My gauge works with the valve in , and all my knobs go to eleven:flipoff2:

The heads were rebuilt about 8k miles ago when I put in the new motor (4.6).

I pulled the codes. Looks like two "multiable misfire" codes, MAF, O2 sensors, and a Cam sensor. I reset the codes, and I've driven ~40 miles so far, and the light has not come back on, and the truck has ran normal.

I have a spare fuel pump ready to go in, if the pump turns out to be the problem...maybe I'll just put it in anyway.

It's hard to pinpoint because it does not do this all the time....

PT,
speaking of cobbling together fuel pumps. Have you had any long term luck with the AC Delco pump that has the same specs (don't have the part #handy)?
It seems as if the original equipment pumps will last 15+ years( if you change the fuel filter when you're supposed to) yet I can't seem to get much more than a year out of any of the other sustitution pumps. I'm at the point where I just spend the extra $$$$ for the genuine article.

My gauge works with the valve in , and all my knobs go to eleven:flipoff2:
LOL, I hear that quite often. I did not use them for client's trucks due to the whole warranty of a part not spec'd for that application. BUT, in those where I did the install, or oversaw the install, they lasted fine. I've had a Mazda truck pump in my trail rig for four or five years and at least 70K miles (I carried a spare last year during the rallye though).

The funny thing is that I think the Autozone part lasts as long, if not longer than the more expensive NAPA part.

Be sure to check all your ground circuits for a problem like this. You can use a tire gauge to check your fuel pressure in a pinch. Best to borrow the tire gauge when you do this though.

JP

Be sure to check all your ground circuits for a problem like this. You can use a tire gauge to check your fuel pressure in a pinch. Best to borrow the tire gauge when you do this though.

JP
Hey, you got a tire gauge I can borrow?

Sure come on by

I had a similar experience at Tellico a few weeks ago. It would idle fine but apply any gas and it would bog, backfire, and had no power. It would come and go as your problem does. After I got to an obstacle I couldn't attempt because of lack of power, I had someone check the fuel filter while I checked MAF, ect under the hood. After checking all the usual things it was still having the same problem. At this point I'm just staring into the engine bay thinking "man it's taken me years to get the drivetrain built to hold up and now I can't even keep my motor running, what the crap!" when I noticed the large hose behind the air filter was slightly disconnected from the filter cannister. Turns out that the intake was sucking air in downstream of the MAF and causing this problem. At first when the engine torqued, it was just enough to open a gap and cause the problem but would go away. Then it separated all toghether and that's when we started looking for the problem. May not be your problem but worth checking into and it would be great if it turns out to be that simple.

Tis

4+ years on an Autozone pump here...

Gone about 250 miles so far and the problem has not returned... Something must have been wet???

Could be speed sensor as well.

That would be my guess.

Could be speed sensor as well.

That would be my guess.

VSS would only drop the odd cylinders and the error codes would reflect specific cylinders, not multiple, random misfires.

Dan, the way you guys wade the river I am suprised you do not run a divers tank in the center console...:laughing: :laughing:

4+ years on an Autozone pump here...

Thats 'cause you drive like a pussy:flipoff2:

Nah, its just strange that I put a genuine pump ('cause the whole assembly was junk) in one of my rigs like 9yrs ago, still runs strong. The Swamp Slut seemed to go through substitute pumps, AC Delco,NAPA and Autozone, she's had 'em all, in about 1 year each (once it was one year to the day). I just had to put a genuine pump in as the whole plastic assembly had gone to hell, but now I'm switching to an oil burner so I'll never know if it made the difference.:shaking: