98 5.7L hiccups bad at 40mph

[ral50]

my silverado 1500 jerks at about 40mph when in lockout. It feels like the engine cuts out but it only does it when in lockout. If I hold the brake slightly to disengage lockout it doesnt do it. It jerks enough to hear backlash in the rear end.It also stumbles a bit, off idle. When cold (open loop) it runs fine, no stumble, no hiccup at 40. This all started when i picked up the truck from the local shop. It had an o2 senser, new fuel injection and new ac plugs installed. It also has new wires,cap,rotor, and tps. When I returned it to the shop they checked their work and drove it with their scanner and checked the trans functions.They said it was the torque converter lockout , but their scanner showed no problem with the tranny. Everything checked out ok. They suggested changing the tps, which I did, but no change. In the interest of a second opinion I took it to a tranny shop. They also drove it with scanner and could find nothing, though they think it is either the engine cutting out or a bad sensor . If anybody has any ideas I would appreciate hearing them........thanks

[j cAT]

many of your symptions point to the engine...when the transmission enters lock up at 43mph the engine stumbles giving the impression of a transmission failure...

you had a lot of parts in the ignition replaced....these parts if defective in manufacture or of the incorrect spec for your vehicle is most likely the problem....

issues of plugs cracked...improper install , gap...wires routed wrong cross firing or just open[no resistance] or the wrong resistance..etc..etc..

by retreving the DTC for the engine you should be able to narrow this down..

[ral50]

the most recent scan showed no codes. It did show a somewhat erratic tps % so I swapped it with a new one with no change. My next move is to check the wiring between the tps and ecu. Also I will check the condition of the cap, rotor and dist shaft play. does this make sense? If that isnt it I think its time to buy a scanner and start checking other sensors. What do you think of the actron 9185? Does anyone know if it will read cam retard?

[j cAT]

I would jump on the wires/plugs...compare resistance with the spec . and look for plug color differences .. check the spark with the plug removed ground out the plug body...is the spark blue or yellow...

[ral50]

actually, with the exception of the plugs, the rest of the ign parts were replaced a few months prior to this problem.I had installed bosch plugs ,but the tech at the shop said only ac delco plugs should be used so I had them replaced when they did the fuel inj,etc. But I will check them anyway as per your suggestion.I'll post my results......

[j cAT]

Originally Posted by ral50

actually, with the exception of the plugs, the rest of the ign parts were replaced a few months prior to this problem.I had installed bosch plugs ,but the tech at the shop said only ac delco plugs should be used so I had them replaced when they did the fuel inj,etc. But I will check them anyway as per your suggestion.I'll post my results......

the plug may have a crack,,,so small that you can't see...this can be your problem as well as the wrong plug/gap....recheck for the correct spec and the condition....


I have used bosch +2 plugs with no issues....but many here at the forum say they are junk...

[ral50]

Latest update..............after extensive troubleshooting,scanning, checking plugs , wires etc., it turns out that the injectors were installed incorrectly. All of the injectors were in the wrong holes. The amazing thing is that it ran as well as it did and that it passed calif. emissions. The lesson here is don't overlook the obvious. Thanks for your suggestions.............