Auto Service World
Feature   March 1, 2002   by Rick Cogbill a.k.a. Slim Shambles

Puddles in the Plenum

"I just got me a dog, announced Beanie during coffee break.Tooner paused between bites of a Snickers bar. "What brought that on?" he asked.Beanie shrugged. "No reason. I just thought a dog would make ...

“I just got me a dog, announced Beanie during coffee break.

Tooner paused between bites of a Snickers bar. “What brought that on?” he asked.

Beanie shrugged. “No reason. I just thought a dog would make a great companion.”

“Ah,” said Basil, as he carefully arranged pickles and olives on his Dagwood sandwich. “The lad is lonely. The new romance must have hit a snag.”

Beanie bristled, but said nothing. I chuckled. His second date with Samantha the parts delivery girl had gone even worse than the first, but that’s another story.

“I’ve only got one piece of advice about the dog, Bean,” I said. “Watch out for the puddles.”

“Yeah,” agreed Tooner. “Until he’s housebroken, never walk into a room with the lights off.”

“Speaking of housebroken,” I continued, “I think it’s time Beanie handled a diagnosis all by himself.” I tossed him some keys. “Bring in this ’93 Jimmy after coffee and see why it runs rough at idle. It’s also hard-starting when warm.” Beanie’s eyes lit up, partly because we’d changed the subject.

I watched our young protg as he attacked the problem at hand. The Jimmy had a 4.3 litre Vortec engine, code W, with Multi-port Central Fuel Injection. The first thing Beanie noted was the black residue in the tailpipe. The spark plug he pulled from the R/H bank was also sooty, indicating a rich fuel mixture. “I scanned for codes,” he said, “but there aren’t any. However, the Fuel Trim readings are 108, instead of 128. Doesn’t that mean the computer is trying to lean out the injector?”

“Yes,” I replied. “You’re definitely getting too much fuel and the ECM is attempting to compensate.”

Beanie held up a printout. “I also checked out the service bulletins, and they say that the first thing you do on these Vortec engines is clean the fuel injection system. Apparently, the poppet valves at the end of the injector tubes can stick, leaking fuel into the cylinders.”

“Do you think that’s the case here?” I asked.

“Well, I also did a fuel pressure test, and it slowly bleeds down when you turn the key off.” It made sense. A fuel leak would explain the poor idle and the hard start warm.

Confident that we had found our culprit, I told Beanie to go ahead with the injector service. Afterwards there was some improvement, but not enough.

“Maybe we’ve got one bad poppet valve,” he suggested.

“Pull all the spark plugs,” I said, “and let’s see which cylinder is the problem.” To our surprise all the spark plugs on the R/H bank were black and sooty, but the plugs on the L/H bank were pure white, indicating a very lean mixture on that side of the engine.

“How can half the engine be rich and the other half lean?” The Bean was stumped.

Basil was watching our progress. “These engines use a Variable Tuned Split-Plane Intake Manifold design,” he remarked. When he saw our blank looks, he continued. “A Tuning Valve Solenoid is used to switch the manifold from Split-plane mode at idle to Single-plane mode at mid-range. At high speed, it reverts back to Split-plane. Maybe that tuning valve solenoid is malfunctioning.” He shrugged. “It’s a long shot.”

To his credit, Beanie processed that information faster than I did. “How do I check that?”

Basil pointed to the plastic cover in the upper intake that had ‘VORTEC’ written on it. “Remove that cover, and then take out the tuning valve solenoid directly underneath.”

Beanie did, and handed me the valve to examine. Out of curiosity, he took a flashlight and peered down the hole into the manifold. “I’ve found it!” he suddenly shouted. He danced around in circles, chanting “Watch out for the puddles; watch out for the puddles!”

I looked inside and, sure enough, there was a puddle of fuel in the lower manifold on the side that fed air to the R/H bank of cylinders. The other side was dry. By removing the upper intake and central fuel injector assembly (the famous ‘spider’), we could see where the fuel pressure regulator was leaking. Regulators are not sold separately, so a complete injector assembly was needed to fix the problem.

“$800 for a new assembly!” exclaimed Beanie the next day. “Good thing we found a used one.”

Tooner agreed. “Cleaning up puddles can be costly,” he said. “Speaking of puddles, how’s the new puppy coming along?”

Beanie looked glum. “Lousy,” he said. “I invited Sam over to see my new dog.”

Tooner raised an eyebrow. “What’s the matter; didn’t she like Rover?”

“She did until she picked him up.”

“Don’t tell me…”

“Yep. His pressure regulator leaked all over her shirt.”

(Thanks to John Cornett-Ching of Summerland Auto-Tech in Summerland, BC, for this month’s technical problem. If you’ve got a good story to tell, e-mail Rick at

About The Writer

Rick Cogbill is a freelance writer living in the Okanagan valley of Southern British Columbia. A licensed technician with over 25 years in the automotive repair industry, including ten years as a shop owner, Cogbill creates his comic scenarios with Slim, Basil, Tooner, and The Bean out of actual case histories. “What you have just read is true,” drawls Slim Shambles. “Only the names have been changed to protect my hide!”

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