'98 Mustang 4.6 Problem

I just had the intake and radiator replaced on my 98 Mustang 4.6 GT and the engine is running horribly. Under acceleration it feels as though it is misfiring or that I have shifted into a higher gear to quickly. There is no power and the car bucks significantly. The shop that did the work can’t find the problem. Any suggestions?


What part of the intake did you have replaced, and why? Was this crash damage?

The whole intake manifold was replaced bc it had cracked. Apparently this is a common problem with the 4.6L as those from this era had a plastic intake. There was a warranty recall on this by Ford which was missed by the previous owner and it lasted 150,000 mi without a problem. The radiator light was continually coming on, indicating a coolant leak and that leak was identified by two separate mechanics as a crack in the intake. No accident damage. Other than the radiator light coming on a week or two after filling the radiator the engine was running perfectly before the $1,000 service for the intake and radiator. Now Im wishing I just kept filling it every 2 weeks instead of spending the $$$. Thanks for the response!

If the engine was running normally before the intake manifold replacement it should still run normally afterward.

Take it back to whoever did the work and let them fix it. Something is not right, and they should stand behind their work. C’mom, didn’t they test drive the car after they worked on it? Did it run “horribly” right away?

Just out of curiosity, why was the radiator replaced, and who did the work? Was it a Ford dealer or an independent mechanic?

How many miles on the car now?

It is back with the shop now for the second time since the replacement. The first time I took delivery it was idling very rough (almost stalling at a stop) and that problem was solved when I returned it the first time. Now this new problem has arisen in the week since and I returned it to the shop yesterday. It idles normally now but lacks power and bucks during acceleration.

The radiator was replaced bc they claimed it was full of deposits that were limiting flow. I looked into it when empty and could see some mineral build-up, but the engine never ran hot even during 110 degree summers here in Phoenix.

I agree they should work until it is fixed, but they seem slightly inept and today called to say they cant find anything wrong, so I was just trying to see if there is something obvious that I could be missing. Thanks again for the help!

The idiots I am working with are unfortunately a PepBoys. They undercut the other estimates I received for the intake and radiator by $300 so I went with them. Clearly a HUGE mistake.

It has 153,000 miles now…

Yeah, as you found out, the mechanics at chain operations are rarely the better, more experienced ones.

If they are unable to make the car run properly, talk to their service manager (assuming that there is one, and that he can speak English), and request at least a partial refund of the labor costs that you paid. (Ask for a full refund on labor, and then settle for less if necessary.) Obviously, you can’t ask for a refund on the parts that were installed.

If you can get some money refunded, take the car to a competent independent mechanic who can figure out what was screwed up by the guys at Pep Boys.

I’ve heard that the intake manifolds cracking on these engines can allow coolant to get down into the spark plug tubes, and thus interrupting the proper operation of the spark plugs. These engines use coil-on-plug ignition units; I’d suggest removing each of these and seeing if one or more spark plugs tubes have coolant in them.

Thanks for the suggestion. Could this have happened during the intake replacement? The engine was running perfectly (I always said it was amazing for an engine with 150,000 mi) before this service.

Pep Boys! You didn’t tell us that. What were you thinking?

Get away from them and take your Mustang to an independent mechanic who can fix the car. Search the “Mechanics Files” on the CarTalk homepage if you don’t already have an independent mechanic.

DO NOT shop for automotive work by price. Quality work is worth the extra money.

Pep Boys? Are you crazy?

Follow VDCdriver’s advice, but get away from Pep Boys, and don’t go back, unless it’s just to buy oil and filters.

They would’ve dried out by now. They messed something up. Probably the connections to the coils and/or injectors. A long time ago, I went to Pep Boys once for some brake work. Never ever would I go there again. They break things instead of fixing things.
Take it to a good Ford dealer and if they will write up the damage they find, maybe you can force Pep Boys to cover the bill from Ford to fix it.

Thanks for all the input. I am just frustrated as I was contemplating even having this done in the first place bc the car isnt worth more than $3,000. Unfortunately I am not in a position to buy something else and bit the bullet. Now I have a barely driveable car and am out $1,100 instead of a perfectly reliable/running (albeit slowly leaking) car.

If it’s any consolation… The manifold would have eventually split wide open.

I’m with Tardis for the most part. They should look at the injectors and COPs. Is your CEL on? If not, does the CEL work? With this kind of performance if an injector or COP is bad, you should have a code and PEP Boys should be checking with the scanner. I am not surprised at all that the engine is still very strong in this car. They are great engines.

If there is no CEL, maybe something was not sealed when they installed the intake manifold. You could have a vacuum leak or a coolant leak into the intake tract.

FYI, there was never a recall on the composite intake manifolds. Ford’s response to the problem was to issue a TSB allowing the dealers to replace ruptured manifolds on police and livery vehicles. Other Ford owners got mad and made a successful lawsuit. Ford settled and agreed to replace ruptured manifolds and pay for the ones already replaced by their dealers or independently. The court figured out that if your car was old enough, you got reasonable service out of it so coverage was not infinite. Your '98 was definitely over the limit.

The all-composite manifolds are less expensive, lighter and flow better than metal ones. Other manufacturers experimented with them as well and the results were not always great for them either. Ford’s molding procedure and material resulted in a manifold that tended to rupture near the bottom the front coolant crossover because the material did not flow properly in the casting process. Rupture there tended to be catastrophic, opening a long gash across across the bottom of the crossover. Depending on the vehicle this often puked coolant into the alternator killing that as well. I have seen some very good pictures posted on the web.

More recently, the ones that have not ruptured catastrophically seem to be cracking at a coolant nipple on the rear of the engine. Unfortunately the revised ones, with a metal coolant crossover, seem to do that as well. What I have seen reported more than that, however, is the coolant outlet develops cracks near the coolant nipple bolts and the ring that supports the thermostat recedes. These, both, cause slow leaks and may seal themselves, for a time, when the coolant is warm. The leak only gets worse, though, for those not in tune with their vehicles.

What kind of manifold did they use to replace it, Ford or Dorman? Is this a manual trans car, or automatic? I agree that PEP Boys broke your car. You should get pretty insistent with them about fixing this. There should be plenty more miles in your 4.6 L engine and they owe it to you to make it right. You may be in small claims court territory. You won’t need a lawyer there, just a good argument for the judge.

Went in today to test drive the Mustang with a mechanic to explain what is wrong and the problem had magically disappeared. The mechanic claimed he had done nothing to it and that there were no codes from the computer. I think I am getting the run around, but for now the car is running as well as it did before the service. They were nice enough to tell me to bring it back if the problem returns which I will obviously do and insist on a mechanic riding with me on the spot. Thanks for all the advice. I hope this is the end of my problems!

If it comes back, check for a coolant leak from the heater hose at the back of the manifold. A leak there will flood the nearby plug well and cause misfires.

That makes me think that it would be a good idea and it would not kill them to pressure test the cooling system.